Class 8

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.3 Chemical Reaction offer valuable context and analysis.

WBBSE Class 8 Science Chapter 2.3 Question Answer – Chemical Reaction

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Which of the following is oxdising agent:
i) Cl₂
ii) H₂S
iii) H₂O
iv) NH₃
Answer:
i) Cl₂

Question 2.
Which of the following is not an enzyme
i) Amylase
ii) Lipase
iii) Carbohydrate
iv) Ranine
Answer:
iii) Carbohydrate.

Question 3.
Which gas is used for welding-
i) Cl₂
ii) O₃
iii) CH₄
iv) C₂ H₂
Answer:
iv) C₂ H₂

Question 4.
If limestone is heated we get-
i) slakelime
ii) quicklime
iii) carbon
iv) carbon-monoxide
Answer:
ii) quicklime

Question 5.
If kerosene oil is heated we get-
i) heat
ii) light
iii) heat and light
iv) none of the above
Answer:
iii) heat and light.

Question 6.
Carbon dioxide turns c!ear lime water-
i) red
ii) blue
iii) milky
iv) colourless
Answer:
i) milky.

Question 7.
Ionic compounds are more soluble in-
i) ether
ii) benzene
iii) chloroform
iv) water
Answer:
iv) water

Question 8.
Which of the following is true-
i) enzymes are indispensible in digestion of food
ii) enzymes are required to produce energy from food
iii) without enzymes no cell can survive
iv) all the above statements are true
Answer:
iv) all the above statements are true

State whether True or False : (1 mark for each question)

1. Energy is required to initiate a chemical reaction.
2. Water is the only solvent.
3. Kerosene and benzene can dissolve ionic compounds.
4. The action of catalysts is called catalysis.
5. Most of the enzymes are protein in nature.
6. Rusting of iron is a physicsl reaction.
7. Combustion of yellow-coloured sulphur powder in the combustion spoon will produce sulphur dioxide.
8. For extraction of metal from its ore, a process of oxidation is taken help of.
9. Oxidation can not occur alone in any reaction, reduction must occur along with it.
10. A coating of synthetic enamel paint on iron can prevent rusting.
Answer:
1. true
2. false
3. false
4. true
5. true
6. false
7. true
8. false
9. true
10. true

Fill in the blanks : (1 mark for each question)

1. Chemical reactions are done by ____.
2. Chemicals participating in a reaction are called ______.
3. Renine is a ______ breaking enzyme.
4. ______ is needed in combustion.
5. The supply of oxygen in atmosphere is due to ______.
6. Baking soda is an ______ compound.
7. Substances that can speed up specific chemical reactions are called ______.
8. Arhar dal or seeds of watermelon contains an enzyme called ______.
9. Ammonia makes the phenolphthalein solution ______.
10. Burning of any fucl is ______.
Answer:
1. atom
2. reactants
3. protein
4. Oxygen
5. photosyntesis
6. ionic
7. Catalysts
8. urease
9. pink
10. exothermic

Match the following : (1 mark for each question)

Column A	Column B
a) In acid phenolphthalein is	i) reducng agent.
b) Phenolphthalein is a	ii) exothermic
c) Carbon monoxide is a	iii) colourless
d) Cl2 is a	iv) exothermic reaction
e) Burning of any fuel is	v) melts iron
f) Burning of C2H2 (acetylene gas)	vi) indicator
g) Heat and light during welding come from	vii) oxidising gas

Answer:
a) In acid Phenolpthalein is colourless.
b) phenolpthalein is a indicator.
c) Carbon monoxide is a reducing agent.
d) Cl₂ is a oxidising gas.
e) Burning of any fuel is exothermic.
f) Burning of C₂ H₂ (acetylene gas) melts iron.
g) Heat and light during welding come from exothermic reaction.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
Give ar example of a catalyst.
Answer:
Mar:ganese dicxide.

Question 2.
Give an example of positive catalyst.
Answer:
Manganese dioxide.

Question 3.
Give an example of negative catalyst.
Answer:
Concentrated H₂ SO₄.

Question 4.
Write a name of enzyme.
Answer:
Amylase.

Question 5.
Write a name of protein breaking enzyme.
Answer:
Tripsine.

Question 6.
Write a name of lipid breaking enzyme.
Answer:
Lipase.

Question 7.
Write a carbohydrate breaking enzyme.
Answer:
Amylase.

Question 8.
Carbohydrate type of food lastly turns into what?
Answer:
Glucose.

Question 9.
What we lastly get from protein type of food?
Answer:
Amino Acid.

Question 10.
What is end of fat breaking enzyme?
Answer:
Fatty acid and Glycerol.

Question 11.
Name some solvents.
Answer:
Water, kerosene, benzene, turpentine oil are uesd as solvents.

Question 12.
Define reactants.
Answer:
Chemicals participating in a reaction are called reactants.

Question 13.
Give an example of ionic compound.
Answer:
Baking soda is an example of ionic compound.

Question 14.
What are catalysts?
Answer:
Substances that can speed up specific chemical reactions are called catalysts.

Question 15.
What is endothermic reactions?
Answer:
Chemical reactions that absorb heat from the surroundings are called endothermic reactions.

Question 16.
What happens when parafin, kerosene, coosking gas are burnt?
Answer:
They produce heat and light.

Short Questions & Answers : (2 marks for each question)

Question 1.
Which living things can make food through photosynthesis?
Answer:
The green plants and some bacteria convert solar energy into chemical energy of food through photosynthesis.

Question 2.
Why do you think are there ‘dark rooms’ in studios?
Answer:
When light falls on a photographic film, many reactions occur and the film gets ciarkened. so to prevent the film from light ‘dark rooms’ are there in siudios.

Question 3.
Why solvent is necessary in a chemical reaction?
Answer:
Mere mixing of the two powdered solids is not sufficient for a chemical reaction. The solvent separates the ions and molecules in the reactants and thus the reaction begins.

Question 4.
No bubble is evolved if a mixture of dry NaHCO₃ and tartaric acid crystals is shaken with benzene or kerosene. Why?
Answer:
Baking soda is a ionic compound. Solvents like kerosene. benzene or turpentine oil can not dissolve ionic compounds. Moreover, tartaric or any other acid must give H^{+ions for reaction. Such an incident can occur in water, but not in a slovent like kerosene or benzene. So the reaction will not ensure in such solvents.

Question 5.
What are exothermic reactions?
Answer:
Chemical changes that evolve heat are called exothermic reactions. Examples of some exothermic reactions are:
Burning of carbon C + O₂ → CO₂ + heat
Combustion of methane CH₄ + 2O₃ → CO₂ + 2H₂O + heat.

Question 6.
What are endothermic reactions?
Answer:
Chemical reactions that absorb heat from the surroundings are called endothermic reactions. Example of endothermic reaction is-
Making quicklime from limestone:
CaCO₃ CaO + CO₂ – heat.

Question 7.
Why the welding personel have to use special spectacles?
Answer:
Heat and light produced during velding come from an exothermic chemical reaction: 2C₂ H₂ + 5O₂ → 4CO₂ + 2H₂O+ heat
This raises the temperature to above 200° C. Light emitted at such a high temperature contains some ultraviolet (UV) radiation that is very harmful to eyes. For this reason, the welding personnel have to use special spectocles that filter out UV radiation.

Question 8.
What is combustion?
Answer:
From our daily experiences we know that when wood, coal etc are set to fire in open air, heat and light are produced. Paraffin, kerosene, cooking gas also burn similarly in open air producing heat and light. Scientifically this phenomenon is termed as combustion.

Question 9.
What is reduction?
Answer:
In a reaction where oxygen gets eliminated from a compound is called reduction. A reaction? where hydrogen combines with an element or copound is also called reduction.

Long Questions & Answers : (3 marks for each question)

Question 1.
What steps can be taken to protect iron from rusting?
Answer:
i) A coating of coal tar or a synthetic enamel paint can be applied on iron, so that it can not come in contact with air and moisture. This coating prevents rusting.
ii) If zinc is electroplated over iron, it prevents rusting. This process is called galvanization.

Question 2.
What is Catalyst? Write down the characteristics of catalysts.
Answer:
There are many reactions that occur very slowly. However, the addition of minute quantities of some other substances results in much facter reaction. Substances that can speed up specific chemical reaction are called catalysts.

Question 3.
Write the caracteristics of catalysts.
Answer:
Caracteristics of catalysts-

1. Catalysts participate in reaction they catalyze but are regenerated in the end.
2. There is no universal catalyst that can enhance the rate of all reactions.
3. Catalysts must always be found by experiment. Just by looking at an equation one can not say which catalyst will be effective in that case.

Question 4.
How are enzymes important to our body?
Answer:
Enzymes are indispensable in digestion of carbohydrates, proteins and lipids present in food. In our body enzymes are required to produce energy from food. In a cell. there are different enzymes to make proteins, DNA. hormones, components of cell membrane etc. Specific enzymes destroy harmful components formed in the cell. Without enzymes, no cell can survive.

Question 5.
What happens during chemical reactions?
Answer:
During chemical reaction some chemical bonds are broken and new ones are formed; in some some cases ionic compounds are formed; in some cases crystals of ionic compounds are broken to form new subetances; in some others ions react to form new substances. In general. such changes is either evolution of heat or absorption of heat.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.3 Heat offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.3 Question Answer – Heat

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
The quantity of heat gained by a body depends on-
i) mass of the substance
ii)-nature of the substance
iii) rise in temperature of the substance
iv) on all the above three factors
Answer:
iv) on all the above three factors

Question 2.
SI unit of heat is –
i) a) Calorie
ii) Joule
iii) Kelvin
iv) Calorie/joule
Answer:
ii) Joule

Question 3.
The form of energy that produces feeling of hotness is called as –
i) work
ii) energy
iii) heat
iv) none of the above
Answer:
iii) theat

Question a.
Heat necessary to increase 1° C temperature of 10 gm water-
i) 1 Calorie
ii) 1 Joule
iii) 10 Calorie
iv) 10 Joule
Answer:
iii) 10 Calorie

Question 5.
Which of the following has least specific heat capaticy-
i) water
ii), iron
iii) milk
iv) copper
Answer:
iv) copper

Question 6.
Which of the following relations is correct?
i) Q = \(\frac{r}{mt}\)
ii) r = \(\frac{q}{mt}\)
iii) t = \(\frac{mq}{r}\)
iv) m = \({mq}{r}\)
I Where Q is the quantity of heat absorbed or given out, m is the mass of the body, r is specific heat capacity, t is change in temperature]
Answer:
ii) r = \(\frac{q}{mt}\)

Question 7.
Two objects of iron and copper of same mass and same amount is given same heat, which object will became heated up quickly.
i) both at same time
ii) iron will heat up quickly
iii) copper willegeat up quickly
iv) we cannot tell definitely
Answer:
iii) copper will heat up quickly

Question 8.
In which season evaporation rate is high?
i) rainy season
ii) summer season
iii) winter season
iv) in all seasons
Answer:
ii) summer season

Question 9.
If impurities are mixed with pure substance then-
i) its boiling point would remain same
ii) its boiling point will decrease
iii) its boiling point will increase
iv) its boiling point may some time increase or decrease
Answer:
ii) its boiling point will decrease

Question 10.
If area of upper surface of any liquid increase-
i) evaporation increase
ii) evaporation decrease
iii) boiling point increase
iv) boiling point decrease
Answer:
i) evaporation increase

Question 11.
Which of the following is fastest?
i) evaporation
ii) boiling
iii) none of the above
iv) both are same
A) Answer:
ii) boiling

Question 12.
Boiling occures-
i) at any temperature and any pressure
ii) at fixed pressure specific temperature
iii) at any pressure fixed temperature
iv) none of the above
Answer:
ii) at fixed pressure specific temperature

Question 13.
If at 0° C temperature, 80 calorie heat is given to 1 g ice then temperature would be-
i) 0° C
ii) more than 0° C
iii) Less than 0° C
iv) 10° C
Answer:
i) 0° C

Question 14.
Transformation of liquid from solid is called-
i) melting
ii) boiling
iii) condensation
iv) freezing
Answer:
i) melting

Question 15.
Which of the following has highest heat capacity-
i) soil
ii) air
iii) water
iv) none of the above
Answer:
iii) water

Question 16.
– is neither created nor destroyed, it can only changed one form to another.
i) mass of body
ii) heat
iii) work
iv) energy
Answer:
iv) energy

State whether True or False : (1 mark for each question)

1) Glass, fat, wax have fixed melting or freczing points.
2) Melting and freezing point of ice is 0° C.
3) Melting point of mercury is 0° C.
4) If ice melts into water its volume increase.
5) A liquid gives up heat when it freexes into a solid.
6) If pressure increase melting point of a substance increase.
7) Transformation of liquid from vapour is called condensation.
8) Boiling point of a liquid does not depend on the area of upper surface.
9) Graphite is bad conductor of heat.
10) In industrial belt fog is mostly seen at the time of winter.
11) Density of hot air is less.
12) melting point of wax is fixed.
13) At 0° C temperature if 80 calorie heat is given to 1 g ice temperature remains uncharged.
14) Volume increases during melting of cast iron.
15) Pressure of vapour in a closed container increases with the increase in the amount of vapour inside.
16) Condensation of water vapour in air produces cloud.
17) Builfing materials should be good conductor of heat.
18) Glass is a bad conductor of heat.
Answer:
1) false
2) true
3) false
4) false
5) true
6) false
7) true
8) true
9) false
10) true
11) true
12) false
13) true
14) false
15) true
16) true
17) false
18) true

Fill in the blanks : (1 mark for each question)

1) Heat is measured with __________.
2) SI unit of heat __________.
3) Heat is a kind of __________.
4) In solid heat is transfered by __________ process.
5) ________ has highest specific heat capacity.
6) Heat _________ the volume of any object__________.
7) Heat comes from sun to earth by __________ process.
8) Dew is the example of natural __________.
9) Specific heat of water __________.
10) The amount of Heat required to increase 1° C temperature of 1 g water is __________.
11) Heat lost by the hot body = Heat __________ by the cold body.
12) If __________ increase boiling capacity increases..
13) Heat capacity = mass of the body x __________.
14) In conduction heat is transferred by __________.
15) The density of the solid ice is less than the __________ water.
16) The process in which a liquid changes very rapidly into its __________ is called boiling.
17) A __________ is necessary for the floe of heat through conduction and conversation.
18) in __________ hot liquid remains hot and cold liquid renains cold for a long time.
19) The houses made up by hay and mud are __________ in winter and __________ in summer.
Answer:
1) Caloriemeter
2) Joule
3) energy
4) conduction
5) water
6) increases
7) radiation
8) condensation
9) 1 cal/g° C
10) 1 calorie
11) gained
12) pressure
13) specific heat
14) molecules
15) density
16) vapour
17) medium
18) thermoflask
19) warm, cool

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Heat is a kind of	i) to produce a freezing mixture.
b) Condensation of water vapour	ii) is 1083°C
c) Sprecific heat of Lead is	iii) different boiling points.
d) Melting point of wax	iv) less than water.
e) In winter wet clothes dry up	v) bad conductor of heat.
f) Ice and salt are mixed in a fixed ratio	vi) in air produces cloud, dew, fog etc.
g) Freezing point of copper	vii) dyne
h) Different liquids have	viii) is not fixed.
i) Boiling point of water is	ix) quicker than rainy season.
j) Glasswool is	x) 100°C

Answer:
a) Heat is a kind of energy.
b) Condensation of water vapour in air produces cloud, dew, fog etc.
c) Specific heat of Lead is less than water.
d) Melting point of wax is not fixed.
e) In winter wet clothes dry up quicker than rainy season.
f) Ice and salt are mixed in a fixed ratio to produce a freezing mixture.
g) Freezing point of copper is 1083° C
h) Different liquids have different boiling points.
i) Boiling point of water is 100° C
j) Glasswool is bad conductor of heat.

b) Match the column A with column B.

Column A	Column B
a) Boiling point of salty water is more	i) the pull of gravity.
b) Spirit is a	ii) a thin piece of paper.
c) Formation of dew is an example of	iii) than pure water.
d) Heat flow is prevented fully	iv) through radiation.
e) Inside a solid substance	v) volatile substance.
f) Heat comes from sun towards carth	vi) is greater, it evaporates quickly.
g) Heavier air comes downward due to	vii) in a thermoflask.
h) Heat can easily flow through a	viii) natural condensation.
i) When the exposed area of a liquid	ix) heat is transmitted by conduction.
Column A	Column B

Answer:
a) Boiling point of salty water is more than pure water.
b) Spirit is a volatile substance.
c) Formation of dew is an example of natural condensation.
d) Heat flow is prevented fully in a thermoflask.
e) Inside a solid substance heat is transmitted by conduction.
f) Heat comes from sun towards earth through radiation.
g) Heavier air comes downward due to the pull of gravity.
h) Heat can easily flow through a a thin piece of paper.
i) When the exposed area of a liquid is greater, it evaporates quickly.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is heat?
Answer:
Heat is a kind of energy.

Question 2.
Which instrument is used to measure heat?
Answer:
Heat is measured with caloriemeter.

Question 3.
What is SI unit of heat?
Answer:
SI unit of heat is joule.

Question 4.
What is CGS unit of heat?
Answer:
CGS unit of Heat is calorie.

Question 5.
What is the process of solid, changing into liquid called?
Answer:
Melting or fusion.

Question 6.
What is the process of liquid substance changing into solid state called?
Answer:
Freezing or solidification.

Question 7.
Write the name of a substance whose melting point is not fixed.
Answer:
Wax.

Question 8.
Write the name of a substance which increase in volume after melting.
Answer:
Gold increase in volume after melting.

Question 9.
Write a name of a substance which decrease in volume after melting.
Answer:
Ice decrease in volume after melting.

Question 10.
If pressure increase boiling point of liquid increase- using this principle an instrument is made. Write its name.
Answer:
Pressure Cooker.

Question 11.
Name a volatile substance.
Answer:
Ether is a volatile substance.

Question 12.
What is the melting point of mercury?
Answer:
Melting point of mercury is -39.5° C.

Question 13.
Give an example of natural process of condensation.
Answer:
A natural process of condensation is formation of dew.

Question 14.
By which process does heat come to earth from sun?
Answer:
Heat comes to earth from sun by radiation.

Question 15.
How transfer of heat occurs in liquid?
Answer:
through convection.

Question 16.
Why are Igloos made of ice?
Answer:
Ice is bad conductor of heat. inside of Igloo is warmer then the outer environment.

Question 17.
Write the name of two substances which are bad conductor?
Answer:
Diamond and glass are two bad conductor.

Question 18.
Who invented thermoflask?
Answer:
British scientist Sir James Dewar invented thermoflask.

Question 19.
What is the boiling point of liquid hydrogen?
Answer:
The boiling point of liquid hydrogen is -253° C.

Question 20.
If pressure increases does it help or hinder the boiling process?
Answer:
The process of boiling is hindered by excess pressure.

Question 21.
When a liquid evaporates quickly?
Answer:
When the exposed area of a liquid is greater, it evaporates quickly.

Question 22.
What is conduction?
Answer:
The process by which heat flows through a solid substance is called conduction.

Question 23.
What is good conductor of heat?
Answer:
The substances through which heat can flow easily are called good conductors of heat.

Question 24.
What is bad conductor of heat?
Answer:
The substances through which heat cannot flow easily are called bad conductors of heat.

Question 25.
In which layer of water do the aquatic animals feel more comfortable during summer?
Answer:
In lower layer of water acquatic animals feel more comfortable during summer.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is the specific heat capacity of a substance?
Answer:
The specific heat capacity of a substance is defined as the amount of heat required to change the temperature of unit mass of the substance by one unit.

Question 2.
What is the CGS and SI unit of specific heat capacity?
Answer:
In CGS system, specific heat capacity is measured in joules per gram per degree and in SI system. specific heat capacity is measured in joules per kilogram per degree.

Question 3.
Why evaporation of water is faster when poured in a plate than a glass?
Answer:
More exposed the area of a liquid is more quickly does it evaporate. Surface area of plate is greater than glass. So evaporation of water is faster when poured in a plate than a glass, as plate has greater surface area.

Question 3.
Why it takes much time to dry cloth in rainy season?
Answer:
Humidity is greater in rainy season so relative humidity is also greater. So rate of evaporation is slow. As rate of evaporation decreases water of wet cloths does not evaporate quickly so it takes much time to dry cloth in rainy season.

Question 4.
What is latent heat?
Answer:
Latent Heat of a substance is defined as the amount of heat required to change the state of the substance without any change in temperature.

Question 5.
What is freezing or solidification? Is the melting point and the freezing point of a substance same?
Answer:
The freezing point or the solidification point is the fixed temperature at which a liquid starts changing to its solid state.
For a pure substance, the melting point and the freezing point are the same.

Question 6.
Latent heat of fusion of ice is 80 calorie/g, what does this signify.
Answer:
This signifies under standard pressure 80 calorie heat has to be given to ice of mass 1 g and temperature 0° C to convert it into water of mass g and temperature 0° C.

Question 7.
The latent heat of stcam is 537 calorie/g, what does this signify.
Answer:
It signifies that under the standard pressure at 100° C, 537 calorie heat has to be rendered to 1 g of water to convert it into steam of 1 g.

Question 8.
Why are burns caused by steam more painful than those caused by hot water at same temperature?
Answer:
1 g of steam at 100° C releases 537 calorie of heat. For this reason that burns caused by steam are more severe then those caused by boiling water.

Question 9.
What is boiling? How is boiling affected by pressure?
Answer:
Boiling is a process in which a liquid changes into its vapour state at a specific temperature by supplting external heat energy to the liquid.
If pressure increase boiling also increase and if pressure decrease boiling also decrease.

Question 10.
Why is water used as a coolant in car radiators?
Answer:
Since water has a high specific heat capacity. it is used as a coolant in car radiators because it can absorb large ameunts of heat from the car engine without any substantial increase in its temperature.

Question 11.
Why we feel cool when spirit is poured on our hand?
Answer:
Spirit is a volatile substance. It starts to change in gaseous state as soon as it is poured in our hand. It takes the necessary latent heat to change into gascous state from our hand so we feel cool.

Question 12.
Why it takes mu:h time to cook food in mountain region?
Answer:
Hitly areas are of higher altitude than sea level. The atmospheric pressure decrease, due to increase n in inint. So the boiling point of water also decrease. That is why it takes much time to cook food in mountain region.

Question 13.
In summer it is comfortable to stand below a fan when perspiring heavily. Why?
Answer:
When we stand below fan after perspiring heavily, evaporation starts from our body. The latent heat necessary for evaporation of sweat is absorbed from the body, so the body cools down, and there is a feeling of comfort.

Question 14.
What is dew?
Answer:
After sunset the earth begins to radiate its heat and gradually becomes cold, when the earth surface becomes sufficiently cold, then it is saturated with water vapour. When some water vapour of the air condenses to water and separates out from the air. dew is formed.

Question 15.
What is conduction?
Answer:
The mode of transfer of heat energy from one molecule to another molecule in the direction of heat flow, from higher temperature to lower temperature, without the actual movement of molecules from their mean position is called conduction.

Question 16.
What is convection?
Answer:
The mode of transfer of heat energy through a fluid from a place of higher temperature to a place of lower temperature by the actual movement of the molecules is called convection.

Question 17.
What is radiation?
Answer:
Radiation is the process of heat transfer in which heat directly passes from one body to the other body without affecting the medium.

Long Questions & Answers : (3 marks for each question)

Question 1.
What is fog?
Answer:
If there is little or no wind in a considerable space near the earth surface at night, then the air in that atomsphere cools down gradually. As a result, that air is saturated by water vapour. At that time the water vapour present in the atmosphere condenses as small droplets around the suspended dust particles, smoke particles. coal dust etc and continues to float in air. This is called fog.

Question 2.
On What factors the quantity of heat gained by a body depends?
Answer:
The quantity of heat gained by a body depends on three factors.
a) Mass of the substance : amount of heat absorbed by a substance is directly proportional to its mass.
b) Nature of the substance : amount of heat absorbed by a substance depends on the nature of the substance.
c) Rise in temperature of the substance : the amount of heat absorbed by a substance is proportional to change in temperature.

Question 3.
What is melting or fusion? How melting point of a substance is affected by pressure?
Answer:
The melting point or the fusion point is the fixed temperature at which a solid starts changing to its liquid state.
Melting point of a substance is affected by pressure in two ways-
i) The substances which decrease in volume after melting, if pressure is increased on them the melting point of that substance decrease. For example ice. cast iron, antimoni bismath.
ii) Again the substances which increase in volume after melting. if pressure is increased on them melting point increase. For example gold. silver, iron. copper.

Question 4.
What is fuse wire? Why melting point of a fuse wire is low?
Answer:
There is a possibility to catch fire if excess amount of current passes through the conducting wire. So to prevent this danger a wire of low melting point is connected with the circuit. This wire is called fuse wire. A fuse wire is made of a mixture of lead and tin. Since melting point of fuse wire is very low, so it melts in low temperature and it does not allow flow of current through it.

We know that if impurities are mixed with pure substance its melting point becomes low. The melting point of a mixture obtained by mixing point of both lead and tin. That is why, melting point of a fuse wire is low.

Question 5.
What is specific latent heat? What is the SI and CGS unit of specific latent heat?
Answer:
Specific latent heat of a substance is defined as the amount of heat required to change the state of unit mass of the substance without any change in temperature. The SI unit of specific latent heat is joules per kilogram and the CGS unit of specific latent heat is joules per gram.

Question 6.
Discuss the features of conduction.
Answer:
Features of conduction-

1. This mode of transfer predominantly takes place in solids.
2. The molecules of the medium do not leave their mean positions, but they traisfer heat as a result of vibration
3. about their mean positions.
4. The transfer of heat can be in any direction along any path.
5. The process is slow.

Question 7.
Discuss the features of convection.
Answer:
Features of convection-

1. This mode of transfer predominantly takes place in liquids and gases.
2. The molecules of the medium absorb heat, they rise and other molecules of medium come to take their place. Thus there is mass movement of medium.
3. The transfer of heat takes place only in vertically upword direction.
4. The process is faster than the conduction.

Question 8.
Discuss the features of radiation.
Answer:
Features of radiation-..

1. No material medium is required for the transfer of heat.
2. The medium does not play any role.
3. The transfer of heat is in all dircetions along a straight line path in the form of electro magnetic waves.

Question 9.
State the differences between evaporation and boiling.
Answer:

Evaporation	Boiling
i) Evaporation takes place at all temperatures	i) It takes place at the boiling point of the liquid
ii) Evaporation is slow and silent process	ii) Evaporation is a fact and violent process
iii) It takes place at the surface of the liquid	iii) It takes place over entire mass of the liquid
iv) It causes cooling	iv) It does not cause cooling

Question 10.
On what factors the boiling point of a liquid depend?
Answer:
Factors which influence the boiling point of a liquid are-

1. Nature of liquid: Different liquids has different boiling point.
2. Presence of it? purities: Generally boiling point increases if some impurities are dissolved in a liquid.
3. Pressure : If pressure increase boiling point of liquid also increases.

Mathematical Problems : (3 marks for each question)

Question 1.
Specific heat capacity of a substance is 0.12 cal^gm gm° C, mass is 10 gm. If there is 20° C increase in temperature then how much heat is required?
Answer:
Heat required = mass × specific heat × tcmperature
= 10 × 0.12 × 20 calorie = 240 caloric.

Question 2.
To rise temperature of 30 gm water from 20° C to 50° C how much heat is required?
Answer:
Required Heat (H) = m s(t₂-t₁) Here m = mass = 50 gm
s = specific heat capacity = 1 calorie / gm
t₁ = initial temperature = 20° C
t₂ = final temperature =50° C
∴ H = 30 × 1 × (50-20) calorie = 30 × 30 calorie = 900 calorie.

Question 3.
How much heat is required to melt 5 gm ice?
Answer:
Latent heat of fusion of ice is 80 calorie / g.
∴ To melt 1 g ice 80 calorie heat is required
∴ To melt 5 g ice = 80 × 5 calori = 400 calorie heat is required

Question 4.
In a tumbler there is 100 gm ice. 6400 calorie heat is given to it. What will be the result?
Answer:
Latent heat of fusion of ice is 80 calorie / g
∴ In 80 calorie heat melts ice 1 g
∴ In 1 calorie heat melts ice g \(\frac{1}{80}\)
∴ In 6400 calorie heat melts \(\frac{6400}{80}\) g=80 g
∴ Result would be 80 g water and 20 g ice.

Question 5.
How much heat is required for 40 g water to boil and turn into vapour?
Answer:
The latent heat of steam is 537 calorie / g
To turn Ig water into steam needed 537 calorie
∴ To turn 40 g water into steam needed 537 × 40 calorie = 21480 calorie heat.

Question 6.
Mass of an object is 200 gm and specific heat 0.09 calorie / gm 1°C. To rise temperature of that object from 20° C to 90° C how much heat is required?
Answer:
We know required heat h = m s(t₁-t₂)

Here
m = mass = 200 gm
s = specific heat = 0.09 unt
t₁ = 20° C and t₂ = 90° C
H = 200 × 0.09 × (90-20) calorie
= 200 × 0.09 × 70 calorie = 1260 calorie.

Question 7.
Calculate the thermal capacity 200 g of aluminium. Specific heat capacity of aluminium 0° 21 calorie g^-1 °C^-1.
Answer:
Thermal capacity = ms
= 200 × 0.21 calorie / °C = 42 calorie / °C

Question 8.
How much heat is required to rise temperature from -8°C to 50°C of 10 g ice. Specific heat of ice 0.5 caloric gm-1° C^-1.
Answer: Heat would be released in three steps.
First from -8° C ice would become 0°C then from 0° C ice would take latent heat and transform in 0°C water and lastly 0° C water would become 50° C water.
From -8° C to 0° C heat required
= (0+8) 0.5 × 10 calorie = 4 × 10 calorie = 40 calorie
From 0° C ice to 0° C water heat required = 80 × 10 calorie = 800 calorie .
From 0° C-50° C water heat required = 10 × 1 × (50-0) calorie = 10 × 50 calorie = 500 calorie
Total heat required = (40+800+500) = 1340 calorie.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 6 The Structure of Living Organisms offer valuable context and analysis.

WBBSE Class 8 Science Chapter 6 Question Answer – The Structure of Living Organisms

Complete the table : (See Text Book Page 178)

Name of cell	Shape of cell
1. Erythrocyte	Red Blood Corpuscles are rounded and flatened on both sides. They look like a disc.
2. Leucocyte	Leucocyte cells change their shape very often.
3. Muscle cell	Muscle cells are spindle shaped, both ends are tapering.
4. Nerve cell	The nerve cell is comparatively longer than other cells. The cell body is star-shaped or rounded and branches of different shapes remain connected with it.
5. Apical cell of root and shoot	Apical cells of root and shoot are hexagonal in shape, they divided and redivide constantly
6. Cells associated with upward transport of water in plant	The cells of this region are cylindrical in shape.

Complete the table : (See Text Book Page 187)

Characteristics	Plant cell	Animal cell
1. Cell wall	A rigid cell wass formed of cellulose is present	Cell wall is abscent
2. Vacuole	Vacuoles are present	Vacuoles are absent
3. Plastid	Plastids are coloured bodies found only in plant cells	Plastid is absent
4. Centrosome	Centrosome is absent	Centrosome is present near the nucleus

(Complete the table : (See Text Book Page 187)

Correlate the words two columns : (See Text Book Page 187)

Answer the following questions : (See Text Book Page 180-189)

Find out the organ cedes, which perform a function synergistically.
(i) Helps in protein synthesis —

• Lysosome
• Ribdsomc.
• Nucleus
• Golgibody
• Cytoplasm
• ER
• Centrosomc. (IT) Secretory granules.
• Vacuole (Give tick Mark)

Or
(ii) Organelles help in synthesis, storage or secretion of different component —

• ER
• Golgjody
• Lysosome
• Secretory gram tiles

(c) Vacuole (Give tick mark)
Cell organelles functioning antagonistically (Find out)

(i) Synthesis of food and break down of food in plant cell.
Answer:
Mitochondria.

(ii) Synthesis of protein and decomposition or digestion of protein in animal cell.
Answer:
Ribosome.

Write origin of following cell organalles.
(i) Golgi body : Mitochondria/Cell membrane/ER.
Answer:
ER

(ii) Lysosome: Centrosome/Golgivody/ER
Answer:
Centrosome

(iii) ER: Cell membrane/Plastid/Golgi body.
Answer:
Cell membrane.

(iv) Ribosome: ER/Golgi body/Lysosome.
Answer:
ER

(v) Vacuoles of Animal Cell: Nucleus/Ccntrosome/Lysosome.
Answer:
Centrosome.

The terminal cells of nail and hair divide repeatedly and cause increase in length of nail and hair. Which organelle remains hyperactive in these cells?
Answer:
Golgi body.

Leucocytes digest and destroy pathogens inside themselves. During this period which originally increase in number?
Answer:
Lysosomes.

Which cell organelles are increased in number in cells of gastric gland (gland present in stomach) secreting enzymes immediately after taking meal?
Answer:
Mitochondria.

The movement of muscular cells of intestinal wall is very slow. But movement of skeletal muscles are fast. Which cell organelle more in number in the muscle cells of leg and hand?
Answer:
Mitochondria.

Class 8 Science Chapter 6 Question Answer West Bengal Board – The Structure of Living Organisms

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
The smallest structural and functional unit of the body is —
i) tissue
ii) cell
iii) organ
Answer:
ii) cell

Question 2.
One ocular lens is used in —
i) electron microscope
ii) compound light microscope
iii) simple light microscope
iv) Complex light microscope
Answer:
iii) simple light microscope

Question 3.
The shape of red blood corpuscle is —
i) round
ii) spindle
iii) cylindrical
iv) hexagonal
Answer:
i) round

Question 4.
A function of muscular tissue of animal body —
i) stores fat
ii) absorption
iii) provides defence
iv) controls blood pressure
Answer:
iv) controls blood pressure

Question 5.
A function of corrective tissue of animal body —
i) secretion
ii) controls body temperature
iii) creates sound
iv) sesration of glands
Answer:
ii) controls body temperature

Question 6.
A function of nerve tissue of animal body —
i) receives stimulus
ii) controls body temperature
iii) swallowing of food
iv) stores fat
Answer:
i) receives stimulus

Question 7.
A function of permanent tissue in plant body —
i) formation of buds
ii) formation of new leaves
iii) formation of new organs
iv) repair of wounds
Answer:
iv) repair of wounds

Question 8.
Helps in cell division in animal cells —
i) Sysosome
ii) golgi bodies
iii) centrosome
iv) ribosome
Answer:
iii) centrosome

Question 9.
Saline environment is seen in —
i) river
ii) ocean
iii) pond
iv) canal
Answer:
ii) ocean

Question 10.
Excessive lysosomal activities lead to —
i) tuberculosis
ii) plague
iii) AIDS
iv) cancer
Answer:
iv) cancer

State whether True or False : (1 mark for each question)

1) Three lenses are used in compound light microscope.
2) Multicellular organisms can not adapt to the changing environment.
3) Only rod shaped cells are present in the retina.
4) An oval shaped cell is modified into a round shaped cell in case of cancer.
5) the dense, rounded structure present in the cytoplasmis called nucleus.
6) The coiled structure of DNA is called chromatin:
7) Vacuole plays important role in the formation of plant body.
8) Number of RBC decreases abruptly in animals living in high-altitude region.
9) Plants grown in saline water possess salt-filled cells.
10) Generally, larger vacancies are present in plant cell and smaller vacuoles in animal cell.
Answer:
1) true
2) false
3) false
4) true
5) true
6) false
7) true
8) false
9) true
10) true.

Fill in the blanks : ( 1 mark for each question)

1) ……………. is the smallest unit of a living organism.
2) Cell is seen is ……………. not seen by naked eye.
3) In 1674 Dutch scientist ……………. observed living cell for the first time.
4) ……………. consists of a single cell.
5) The organisms can adopt in the changing environment.
6) Algae like ……………. looks like a thread ie filamentous.
7) The shape of ……………. is even changing.
8) ……………. helps in the process of locomotion of Amoeba.
9) The ……………. present in human blood destroy the invading pathogens.
10) ……………. cells are the smallest cells in our body.
11) Muscle cells are ……………. shaped; both ends are
12) The ……………. cells are comperatively longer than other cells.
13) The adipose cell looks like a ……………. es.
14) ……………. cell is the longest cell.
15) Unfertilised ……………. egg is the largest cell.
16) ……………. provides a definite shape to cell.
17) The characters of parents are transmitted to the offspring through …………….
18) On the basis of ……………. number we differntiate one species from another species.
19) ……………. is the control centre of the cell.
20) ……………. are small rounded sacs filled with enzymes.
Answer:
1) cell
2) microscope
3) Lecnwen hock
4) amoeba
5) multicellular
6) spirogyra
7) amoeba
8) Pseudopodia
9) leucocytes
10) blood
11) spindle, tapering
12) nerve
13) ring
14) nerve
15) ostrich
16) cell membrane
17) genes
18) chromosome
19) nucleus
20) lysosomes

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is living thing?
Answer:
The things which perform respiration, digestion, excretion, and reproduction are called living things.

Question 2.
What is cell?
Answer:
The structural and functional unit of the body is called cell.

Question 3.
Who discovered cell?
Answer:
Cells were discovered by Robert Hooke in 1665 when he observed this a slice of cork under his microscope.

Question 4.
Is it possible to see a cell with naked eye?
Answer:
Cell is not seen under naked eye because its size is very small, it can be seen by microscope.

Question 5.
What is the magnification of an Electron Microscope?
Answer:
The magnification of an Election Microscope is 50.000-30,000

Question 6.
Name some unicellular organisms.
Answer:
Organisms like bacteria. Amoeba. Euglena, Paramecium, Chlamydomonas and yeast are formed of one cell only.

Question 7.
Name some multicelular organisms.
Answer:
Organisms like frog. man. tree. Hydra are formed of many cells.

Question 8.
On what factor the shape of cell depends in muliicelluar organisms?
Answer:
In multicellular organisms the shape of cell depends on their metabolic activities or nature of functions.

Question 9.
Where fat is stored in animals body?
Answer:
In animal body the fat is stored beneath the skin.

Question 10.
What type of cell is present in retina?
Answer:
Rod shaped cells are pescnt in ratina which absorbs mild light and cone shaped cells are also present in the retina which absorbs bright light and colour.

Question 11.
What is the shape of Dead store cells?
Answer:
Dead store cells present in seed coat and fruit coat assume the shape of rod, star or bone etc.

Question 12.
With what type of cell the body of Spirogyra is made of?
Answer:
The body of Spirogyra is made up of rectangular cells.

Question 13.
What Amoeba used for moving?
Answer:
Amoeba uses its pseudopodia for moving.

Question 14.
What is the shape of cell of RBC?
Answer:
Red blood Corpuscles are rounded and flattened on both sides, they look like a disc.

Question 15.
How do Muscles cells of human body look like?
Answer:
Muscle cells are spindle shaped both ends are tapering.

Question 16.
What is the shape of nerve cell?
Answer:
Nerve cells are quite long and are star-shaped or rounded and branches of different shapes remain connected with it.

Question 17.
What is the structural steps of living organism?
Answer:
The structural steps of living organism are — (body → organ system → organs → tissues → cell)

Question 18.
What is tissue?
Answer:
A group of cells performing the same function constitutes a tissue

Question 19.
What is cell membrane?
Answer:
The thin membrane present outside the cell is called cell membrane or plasma membrane.

Question 20.
What is cytoplasm?
Answer:
Cytoplasm is a jelly-like semifluid substance between the cell membrane and nucleus.

Question 21.
What is called ‘brain’ of the cell?
Answer:
Nucleus is called the ‘brain” of the cell as it controls all biochemical process of cell.

Question 22.
What is chromatin reticulum?
Answer:
A thread-like structure present inside nucleus arranged is reticulate fashion are called chromatin reticulum.

Question 23.
What are chromosome?
Answer:
Chromosomes are formed from chromatin reticulum. During cell division, Chromatin fibres condense to form chromosomes.

Question 24.
What is gene?
Answer:
Gene is a special structure present in chromosome. The characters of parents are transmitted to the offspring through genes.

Question 25.
What is nucleolus?
Answer:
A distinct, rounded, dense, structure is present inside the nucleus where rebosomes are synthesised, it is called nucleolus.

Question 26.
How many chromosomes are there in human body?
Answer:
A human body cell has 46 chromosomes in its nucleus.

Question 27.
What are prokaryotes?
Answer:
Cells like Bacteria, blue-green algae posses nuclear material without enclosed in membrane, they are prokaryotes.

Question 28.
What are eukaryotes?
Answer:
Most of the plant and animal cells possess nucleus with membrane and nuclear reticulum, they are called eukaryotes.

Question 29.
What is protoplasm?
Answer:
Together nucleus and cytoplasm are called protoplasm.

Question 30.
What are cell organelles?
Answer:
Various minute structures scattered inside cell cytoplasm are called cell organelles.

Question 31.
What is called the power house of cell?
Answer:
Mitochondria is called the power house of ceil?

Question 32.
What are cristae?
Answer:
Finger like projections come out from inner membrams of Mitochondria they are called cristae.

Question 33.
What are called suicidal bag?
Answer:
Lysosomes are called suicidal bag.

Question 34.
What leads to cancer?
Answer:
More lysosomal activities leads to cancer,

Question 35.
What is primordial entriclc?
Answer:
The large vacuole occupies most of the plant cell centrally, pushing the cytoplasm and nucleus towards periphery in the form of a film just beneath the cell membrane, this layer is called primordial utricle.

Question 36.
Which animals have antifreeze protein?
Answer:
The animals living in very dry and cold environment have anti freeze protin.

Question 37.
How fresh water plants float on water?
Answer:
They can easily float on the surface of water due to air cavity in the parenchyma (aerenchyna).

Question 38.
In less oxygenated environment what helps bacteria in respiration?
Answer:
If less oxygenated environment mitochondria are absent in bacteria instead they possess mesome which helps them in respiration.

Question 39.
What is more in cells of endoskelcton?
Answer:
Calcium is more in cells of endoskeleton.

Question 40.
What increases abruptly in animals living in high altitude region?
Answer:
Number of RBC increases abruptly in animals living in high altitude region.

Short Questions & Answers : (2 marks for each question)

Question 1.
What does a cell look like?
Answer:
The shape of cells varies from one organism to another. The shape of cells is related to the functions they perform. Cells may be rounded, spherical, oval, elongated, tubular, cubojdal, disc-shaped, kidney shaped, spindle shaped or irregular.

Question 2.
What is a tissue? Into how many groups it can be classified?
Answer:
Division of labour in protoplasm of different cells results from the evolution life and causes the difference in functions. Due to occurrence of these type of phepiornena specialised types of cells originated. Collection of these specialised cells are known as tissue. Tissues can be divided into the following types :

• Plant tissues
• Animal tissues.

Question 3.
What are the different types of plant tissues?
Answer:
Plant tissues are mainly classified as —

• Meristematic tissues
• Permanent tissues

Question 4.
What are the different types of animal tissues
Answer:

• Epithelial tissues
• Connective tissues
• Muscular tissues
• Nervous tissues.

Question 5.
What are different parts of an animal cells?
Answer:
Animal cells have following parts – Cell membrane, Cytoplasm, Nucleus, Cell organelles, Mitochondria, Endloplasmic Reticulum, Golgibodies, Lysosomes, Ribosomes and Centrosome.

Long Questions & Answers : (3 marks for each question)

Question 1.
Which organs in human body are capable of performing one or more than one functions?
Answer:

• Stomach and small intestine for digestion of food.
• bung for respiration
• Heart for transperation of blood (circulation)
• Kidney for elimination of metabolic waste (excretion)
• Brain for receiving external stimulus and converting it into response.

Question 2.
How many types of Microscope arc there, explain briefly?
Answer:
a) Simple light Microscope : Structurally it is simple because only one ocular lens is used. Its magnification is 15-20x.

b) Compound light Microscope: Three lenses are used, namely – ocular lens, objective lens and condenser lens. It is operated by using a beam of sunlight or artificial light source. A mirror or reflector is used fortius purpose. Its magnification is 2000 – 400.0x.

c) Electron Microscope : In this microscope eletromagnetic lens is used instead of glass lens. Magnification is 50,000 – 30,000x. It is fully computerized. The materials to be observed cannot by seen directly. Instead of that photographic films are used.

Question 3.
What types of physiological function are going on in an animal body?
Answer:

• Digestion, Absorption, Assimilation and Egestion (Nutrition)
• Gaseous exchange and Energy production (Respiration)
• Transport of food, oxygen and carbon dioxide (Circulation)
• Expulsion of harmful metabolic wastes (Excretion)
• Change of place in search of food, shelter etc. (Locomotion)
• Response to external stimulus (nervous co-ordination)
• Increase in number and perpetuation (Reproduction)

Question 4.
Describe the different functions that occur in plants throughout a day.
Answer:

• Transport of water from soil to the leaves.
• Absorption of sunlight and preparation of food.
• Standing erect.
• Storage and transport of food.
• Formation of flower, fruit and seeds.

Question 5.
What are the functions of meristematic tissue?
Answer:

• Formation of new’ organs.
• increase the length of root and shoot.
• formation of new leaves, axillary buds, new branches and flowers.
• formation of protective coverings.
• formation of conductive tissue.

Question 6.
What are the functions of permanent tissues?
Answer:

• Synthesis, storage and transporation of food.
• Conduction of water.
• Providing mechanical strength and rigidity
• Storage of waste
• Proving buoyancy
• Dispersal of fruits and seeds
• Increasing the power of tolerance of plant organs to external load and pressure.
• Repair of wounds

Question 7.
Describe the functions of Epithelial tissues?
Answer:

• Formation of protective layers over the free surface of internal organs and outside the body
• Absorption
• Secretion
• Elimination of metabolic wastes and foreign substances.
• Formation of exoskeleton (Scale, hairs, nails, hoove, horn etc.)

Question 8.
What are the functions of nerve tissues?
Answer:

• Receives stimulus
• Conduction of impulse
• Co-ordination of internal and external environment
• Controls contraction of muscle and secretion of gland.

Question 9.
Briefly explain the functions of connective tissue?
Answer:

• Providing mechanical strength and framework,
• Connects different internal organs
• Provides defence
• Stores fat and controls body temperature.

Question 10.
What are the functions of muscular tissues?
Answer:

• Movement of appendages
• Helps in locomotion, swallowing of food, peristaltic movement of alimentary canal and primary tract.
• Controls heart beat and flows of blood,
• Controls blood pressure.
• Controls facial Expression
• Causes changes in body postures and gestures.

Question 11
What is ceil wall? what are its functions?
Answer:
The external matrix present around the plant cell is cell wall. It is a non-living, strong and rigid layer surrounding plasma membrane. It is mainly composed of cellulose. Functions of cell, wall are –

• Gives rigidity and shape to the plant cell.
• Allours substances in solution to enter and leave the cell without hindrance.
• Provides protection

Question 12.
Write short notes on – (a) Nucleus, (b) Mitochondria, (c) Ribosomes
Answer:
a) Nucleus — The dense, rounded structure present in the cytoplsm is called Nucleus. It controls all bio-chimical processes of cell, so it is called ‘brain’ of the cell, Nuclear membrane exists outside the nucleus. Semi-liquid nucleoplasm is present inside it. contains network of thread-like structures called chromatin fibres which contain DNA. A distinct, rounded, dense structure is present inside the nucleus where ribosomes are synthesised. It is called nucleolus.

b) Mitochondria — It is rounded oval or rod-shaped. Various types of enzymes, ribosome and nuclic acid (DNA) are present inside its matrix. They produce energy by breaking down nutrients of food. Finger-like projections come out from inner membrances, it is called cristac. They are involved in production of energy (ATP).

c) Ribosomes — Ribosomes are scattered in the cytoplasm of prokaryotes or attached on surface of ER. These are membraneless cell organelles. Protein synthesis is the main function of ribosome. These proteins help in recovery of wounded protions and also helps in new cell formation.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.2 Structure of Matter offer valuable context and analysis.

WBBSE Class 8 Science Chapter 2.2 Question Answer – Structure of Matter

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
In 1903 who had proposed the model of an atom, due to which electrons and protons were known to us?
i) Rutherford
ii) Dalton
iii) Goldstein
iv) Joseph J Thomson
Answer:
iv) Joseph J Thomson

Question 2.
The present concept of the structure of an atom is given by which scientiest?
i) Joseph J Thomson
ii) Goldstein
iii) Niles Bohr
iv) Rutherford
Answer:
iii) Niles Bohr

Question 3.
Which model does not able to explain the stability of an atom?
i) Thomson’s model
ii) Rutherford’s model
iii) Bhor’s model
iv) none of the above
Answer:
ii) Rutherford’s model

Question 4.
Name an atom in which the molecules of that atom does not contain any neutrons?
i) Hydrogen
ii) Oxygen
iii) Sodium
iv) Phosphorous
Answer:
i) Hydrogen

Question 5.
Electron was discovered by –
i) Goldstein
ii) J J Thomson
iii) Niles Bohr
iv) Rutherford
Answer:
iii) Niles Bohr

Question 6.
The correct electronic configuration of sodium is-
i) 8, 2, 1
ii) 2, 1, 8
iii) 2, 8, 2
iv) 2, 8, 1
Answer:
iv) 2, 8, 1

Question 7.
Who discovered neutron in 1953 ?
i) Niles Bohr
ii) James Chadwick
iii) Rutherford
iv) Goldstein
Answer:
ii) James Chadwick

Question 8.
The atom has-
i) Positive charge
ii) negative charge
iii) some times positive and sometimes negative
iv) no charge
Answer:
iv) no charge

Question 9.
Symbol of Ferric ion is –
i) Fe⁺¹
ii) Fe⁺³
iii) Fe⁺
iv) Fe⁺⁴
Answer:
ii) Fe⁺³

Question 10.
Charged atoms are called-
i) isotope
ii) isobar
iii) isotone
iv) ion
Answer:
iv) lon.

Question 11.
The total number of protons and neutrons in an atom is called its
i) mass number
ii) atomic number
iii) mass
iv) none of the above
Answer:
Mtas number.

State whether True or False : (1 mark for each question)

1. Vearly the whole mass of an atom remains concentrated at its centers.
2. John Dalton’s experiment proved the existence of electrons in 1820.
3. Neutrons are electrically neutral.
4. An iron atom is heavier than a gold atom.
5. In a solid the average distance between the molecules is much larger that those in a solid.
6. The kinetic energy of molecules in a liquid increases with increase of temperature.
7. Salt (NaCl) melts at a temperature of about 800° C.
8. Ionic compounds are made of molecules.
9. Liquids have definite shape, but they have not definite volume.
10. The mass of an atom can not be measured directly by any balance.
Answer:
1. true
2. false
3. true
4. false
5. false
6. true
7. true
8. false
9. false
10. true

Fill in the blanks : (1 mark for each question)

1. In 1808 _________ published his atomic theory.
2. The smallest particle of an element that retains the properties of the element is called an ________.
3. Atoms of the same element possessing unequal number of neutrons are called _________.
4. Electrons are ________ charged.
5. The number of protons in an atom is called its _________.
6. The total number of protons and neutrons in an atom is called its ________.
7. The ________ has mass but no charge.
8. Atoms gain or lose ________ to attain stability.
9. When an atom gains or loses an electron, an ________ is formed.
10. When more than one atom combine to form an ion, it is called a ________.
11. Solids have their own shape and ________.
12. Atoms of differfnt elements differ in mass and ________ properties.
Answer:
1. John Dalton
2. atom
3. isotopes
4. negatively
5. atomic number
6. mass number
7. neutron
8. electrons
9. ion
10. radical
11. volume
12. chemical.

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Formula of Ammonium	i) CaCO3
b) Nicls Bohar is a	ii) roughly views like solar system
c) Formula of Calcium carbonate	iii) lins many valency
d) Valency of Aluminium is	iv) has 4 protons.
e) The atomic model	v) Plasma
i) In Cuprous oxide	vi) NH4+
g) Iron	vii) Valency of copper is 1.
h) Nuclars of an oxygen atom	viii) 3
i) Fourth state of a substance is	ix) renouned atom scientist

Answer:
a) Formula of Ammonium NH₄
b) Niels Bohr is a renoined atom scientist
c) Formula of Calcium Carbonate CaCO₃
d) Valency of Aluminium 3.
e) The atomic model roughly views like solar system.
f) In Cuprous oxide valency of copper is 1.
g) Iron has many valency.
h) Nucleus of an oxyen atom has 4 protons.
i) Fourth state of a substance is plasma.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What does the word ‘atoms’ mean in Greck language?
Answer:
Indivisible

Question 2.
Who is the father of atomic theory?
Answer:
John Dalton.

Question 3.
In which year atomic theory of John Dalton was published?
Answer:
Atomic theory of John Dalton was published in 1808

Question 4.
What are an atom made up of?
Answer:
Atoms are made up of three smaller particles, called proton, neutron and electron.

Question 5.
Who discovered neutron?
Answer:
Neutron was discovered in 1912 by Rutherford’s pupil, Chadwick.

Question 6.
What is atomic number?
Answer:
The number of protons in an atom is called its atomic number.

Question 7.
What is mass number?
Answer:
The total number of protons and neutrons in an atom is called its mass number.

Question 8.
What is Isotope?
Answer:
Atoms of the same element possessing unequal number of neutrons are called isotopes. Examples are (protium), (doeterium). (tritium)

Question 9.
What is Isobar?
Answer:
Atoms different elements that have an equal mass number are called is obars of one another. Examples are… H and….He,… C and… N.

Question 10.
What are ions?
Answer:
The atoms which attain positive or negative charges due to gain or loss of one or more electrons are called ions.

Question 11.
What are cations?
Answer:
The positively charged ions formed by the loss of electrons from an atoms are called cations.

Question 12.
What are anions?
Answer:
The negatively charged ions formed by the gain of electrons by an atom are called anions.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is Valency of an element?
Answer:
Valency of an element is a measure of its combining power with other atoms when it forms chemical compounds or molecules. The concept of velence was developed in the second half of the 19th century and helped successfuily to explain the molecular structure of inorganic and organic compounds.

Question 2.
How the pleasant smell of incense sticks spreads through a room?
Answer:
When a iscense stick burns, some volatile compounds present in it evaporate. Molecules of some of these compounds, when inhaled. gives as the sensation of pleasant smell. Spreading of an odour through air is due to motion of molecules in the gas phase.

Question 3.
How can you prove that molecules can spread through liquids?
Answer:
In a glass of water if we add a drop of ink, it spreads slowly through water. This experiment indicates that molecules can spread through liquids.

Question 4.
What are the characteristics of atoms and molecules in a solid?
Answer:
In a solid the atoms and molecules remain in a relatively ordered state and close to each other. In a solid, the atoms or molecules viabrate about their mean position.

Question 5.
What are the characteristics of molecoles in a liquid?
Answer:
Molecules in a liquid are somewhat disordered. They can viabrate, rotate and move through a small distance. This freedom of movement results in a liquid having no sefinite shape, although it does have a definite volume.

Question 6.
What are the characteristics of molecules in a gas?
Answer:
In a gas molecules are moving randomly with different speeds, vibrating and rotating. They are colliding with each other, and are also collifing against the walls of the container. Such incessant motion results in a gas having no xixed volume or shape.

Long Questions & Answers : (3 marks for each question)

Question 1.
What was Rutherford’s general conclusions about atom?
Answer:

1. Most of the space inside an atom is empty.
2. Nearly the whole mass of an atom remains concentrated at its centre. Rutherford named this heavy central part nucleus.
3. The entire positive charge of an atom remains confined to its nucleus.
4. Electrons revolve around thenucleus in various circular orbits

Question 2.
Describe Dalton’s Atomic Theory.
Answer:
Dalton proposed the following postulates about the structure of matter-

1. All matter is made up of indivisible minute particles called atoms.
2. All atoms of an element are identical
3. Atoms of an element are different from the atoms of any other element.
4. A compound is formed by the combination of atoms of two or more elements in simple ratios.
5. Atoms can neither be created nor destroyed.

Question 3.
Describe the structure of electrovalent compound NaCl.
Answer:
NaCl is an electro valent compound.
Electrons arranged in Na are 2 + 8 + 1
Electrons areanged in CL are 2 + 8 + 7
Sodium has I lectron in its valence shell. Chtorine has 7 electrons in its valence shell, which is I short of the octet. Sodium atom loses I electron toi necame Na^–. Chlorine atom gains this electron to become Cl

Na → Na^–
2 + 8 + 12 + 8

Cl → Cl^–
2 + 8 + 72 + 8 + 8

Thus NaCl compound is formed.

Question 4.
What happens when the temperature of a solid is increased?
Answer:
In a solid atoms and molecules vibrate at all temperatures. When temperature is increased kinetic energy of vibration increases. Beyond a certain pointthe vibration became so snergetic that the solid state can not be maintained and the solid is converted to a liquid. This conversion is known as melting.

Question 5.
What happens when the temperature of a liquid is increased?
Answer:
With increase of temperature, kinetic energy of molecules in a liquid increases. Beyond a certain point, the kinetic energy becomes so great that molecules can not be held back in the liquid state. The liquid is then converted to its vapour. This change of state is called boiling.

Question 6.
In the following table, diagrams of the atoms of lithium, sodium, magnesium and chlorine are shown. Complete the table with information regarding the quantities mentioned in it.
Answer:

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 10 Biodiversity, Environmental Crisis and Conservation of Endangered Animals offer valuable context and analysis.

WBBSE Class 8 Science Chapter 10 Question Answer – Biodiversity, Environmental Crisis and Conservation of Endangered Animals

1. Let us try to fill up the table about forest. (Sec Text Book Page no. 243)

2. Let us try to fill up the following. (See Text Book Page no. 244)

Name of things to be] used	Name of component material of forest to be used for taking those things	Source
1. Pencil 2.  Cricket bat 3.  Medicine 4.  Dress/Clothes 5.  Vehicles 6.  Mat 7.  Shed 8.  Fuel	wood wood flower, fruit, root, leaves cottonwood, timber grass, leaves leaves, straw leaves, wood, twings	tree tree medicinal plant seed tree plant plant, tree plant, tree

3. Write the name of plant or animals in the space provided below that can their in these forests. (See Text Book Page no. 244)

• Forests of plants having needle shaped leaves (Pine, Oak, Black Bear, Leopard, Deodar. Garan)
• Forest of deciduous plants (Teak, Arjiin. Ainbaki, Tiger, Elephant, Bison, Sal).
• Forest of everygreen plants (Jamun, Banyan, Mango, Tiger, Deer, Peacock, Neem. Cheetah)
• Forest thorny bushy plants (Babul, Cactus, Blackback, Chimuara, Jackal, Dear)
• Forest of grasses. (Grass, Hogla, Purandi, Rhinoceros, Dear, Zebra, Mongoose)
• Forest of mangrove plants with respiratory root (Garan, Gewa, Baine, Tiger, Estuarine Crocodile, Sundari. Otter)

4. Construct a food chain by choosing at least three orgainisms for the above list. Mention who is the producer, herbivore or carnivore in the food chain. (Sec Text Book Page no. 245)
Answer:

5. See the picture of desert and write your ideas of the following : (Sec Text Book Page no. 259)

Desert
Nature	Climate	Trees	Animals
Sand sandumes	very hot in day time cold in night	cannot be seen, only some	Cannel, rat. Chameleon snake

Plants in the Desert (Page 261)

Discuss with the friends and fill up the table below:

Subject	Necessities) water	Gets from where
Necessity of plants for living		from the ground
Necessity of animals for living	water and food	Oasis, some type of cactus, datepalm

You understand the behaviour of different type of desert plant and animals. Then mention which parts of their body have a role active for living in the desert. (Page 265)

We have already seen how human life is dependent of bio(diversity in various way. (Sec Text Book page no. 272)

Nature of dependence	On which animal have to depend
(1) Food	Goat, fish, sheep, hen
(2) Shelter	Cow, ass, buffalo
(3) Clothes	Polar bear, Penguin
(4) Fuel	Penguin, whole
(5) Commercial	Dear, whale, elephant.
(6) Medicine	Penguin

Write the diverse havitat and cause of gradual extinction of animals provided in the following table after reading the following pages and callccting information from different sources. (See Text Book page no. 272)

Name of animals	Name of the habhitat	Their problems
1. Vulture	Simul, Banyan etc tree	felling down of trees, burial of dead animals.
2. One-horned	wet grass land of jungle	deforestation, marking of houses in that places.
3. Fishing cat	swampy areas	filling of such areas
4. Gangetic Dolphin	near gang a river and its tributaries	decreasing of the depth of water.

Class 8 Science Chapter 10 Question Answer West Bengal Board – Biodiversity, Environmental Crisis and Conservation of Endangered Animals

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Forest of thormy bushy plants —
i) pine
ii) amlaki
iii) garan
iv) cliinkara
Answer:
iv) chinkara

Question 2.
Forest of thormy evergreen plants —
i) arjun
ii) mango
iii) hogla
iv) pine
Answer:
ii) mango

Question 3.
Deer lives in the forest of —
i) grasses
ii) thorny bushy plants
iii) deciduous plants
iv) evergreen plants
Answer:
i) grasses

Question 4.
Crocodile lives in the forest of —
i) grasses
ii) evergreen plants
iii) mangrove plants
iv) bushy plants
Answer:
iii) mangrove plants

Question 5.
Which is not the cause of forest fire —
i) Volcanic eruption
ii) deforestation
iii) lightning
iv) coocking in the forest
Answer:
ii) deforestation

Question 6.
The animal that has eight arms —
i) sea anemone
ii) squid
iii) sea-pen
iv) octopus
Answer:
iv) octopus

Question 7.
The animal that has five arms —
i) starfish
ii) squid
iii) whale
iv) octopus
Answer:
i) starfish

Question 8.
Ostrich is found in —
i) Arabian desert
ii) Sahara desert
iii) Gobi desert
iv) Thar desert
Answer:
iii) Gobi desert

Question 9.
Blue mountain pigeon is found in —
i) Arabian desert
ii) Sahara desert
iii) Gobi desert
iv) Thar desert
Answer:
iii) Gobi desert

Question 10.
A plant in the desert —
i) rose apple
ii) Mesquite plant
iii) teak
iv) bainc
Answer:
ii) Mesquite plant

Question 11.
A small rat like animal —
i) rattle snake
ii) chameleon
iii) porcupine
iv) gerbil
Answer:
iv) gerbil

Question 12.
Arctic animals lay eggs or give birth in —
i) summer
ii) autumn
iii) winter
iv) spring
Answer:
i) summer

State whether True or False : (1 mark for each question)

1. Mesquite plant arc born near the sand dunes.
2. The desert travellers quench their thirst by the use of Jashua plant.
3. Hump of Camel is a storage of water.
4. Camel can drink 25 gallon of water at a time.
5. When the temperature increases some animals of desert go to deep sleep, named aestivation.
6. The most poisonous snake in the desert is cobra.
7. Oceania contains only 50% forests.
8. The third layer of mature forest is made up of canopy cover.
9. Diatom is an unicellular organism.
10. The mother octopus looks after her progenies till she dies by inches due to starvation.
11. Desert covers approximately one fifth of the earth surface.
12. The borders of Rajasthan is covered by the desert Thar.
Answer:
1) true
2) false
3) false
4) true
5) true
6) false
7) false
8) false
9) true
10) true
11) false
12) true.

Fill in the blanks : (1 mark for each question)

1. Forest is the cluster of …………………….. covering a wide range of area.
2. Forest covers …………………….. of total land area of India.
3. Man destroys …………………….. acorn of forest in each second in the world.
4. …………………….. is a kind of marine algae.
5. Luciferin is a …………………….. bound pigment and Luciferase is an ……………………..
6. The majority of the bioluminescent organisms can be seen at …………………….. metre depth of the ocean.
7. …………………….. countries in the world have no forest cover.
8. 64 countries forests cover less than …………………….. of the total land area.
9. Almost …………………….. different species of ants are found in one tree in Peru.
10. If forests are cleaned day by day, the plants, capable of absorbing emitted, …………………….. start declining in number.
11. The cell wall of Diatoms is composed of ………………………
12. Various marine organisms feed on ………………………
13. The tentacles of sea anemone contain numerous cells.
14. Each arm of octopus contains many ………………………
15. The skeleton of shark is made up of ………………………
16. The starfish moves about with the help of the ………………………
17. The oil is like …………………….. to marine life.
18. …………………….. emission is increasing due to various human activities.
19. Avery few …………………….. are found in the vast desert.
20. The fruits of the saguaro cactus look like a ……………………..
Answer:
1) plants
2) 21%
3) 1.5,4) kelp
5) Protein, enzyme
6) 200-1000
7) ten
8) 10%
9) 50
10) CO₂
11) silica
12) Phytoplankton
13) stinging
14) suckers
15) cartilage
16) tube feet,
17) poison
18) CO₂
19) oasis
20) water-melon.

Match the column A with column B.

Column A	Column B
a) The forest floor is the last layer of a	i) an uncontrolled fire
b) The rainforests are vital source of	ii) unicellular organisms
c) It is not possible for man	iii) contains many suckers
d) A forest fire is	iv) inside the sand
c) Excess salts cause toxicity	v) gradually increasing
f) Diatoms are	vi) to sustain without forest
g) Each arm of octopus	vii) well-formed forest
li) The squid catches its prey	viii) many life-saving medicines
i) Gobi desert is	ix) in the tissues of plants
j) Gerbil lives	x) with suckers

Answer:
a) The forest floor is the last layer of a well-formed forest.
b) The rainforests are vital source of many life-saving medicines.
c) It is not possible for man to sustain without forest.
d) A forest fire is an uncontrolled fire.
e) Excess salts cause toxicity in the tissues of plants.
f) Diatoms are unicellular organisms.
g) Each arm of octopus contains many suckers.
h) The squid catches its prey with suckers.
i) Gobi desert is gradually increasing.
j) Gerbil lives inside the sand.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is forest?
Answer:
Forest is the cluster of plants covering a wide range of area.

Question 2.
How much forests cover of total area of India?
Answer:
Forest covers 21010 sq.km of total area of India.

Question 3.
Which year was announced by United Nations as the ‘International Year of Forest’?
Answer:
United Nations annouced the year 2011 as the “International year of forest.”

Question 4.
Name some needle shaped leafy plant?
Answer:
Pine, Oak, Deodar etc.

Question 5.
Name some evergreen trees.
Answer:
Mngo, Jammun, Banyan etc.

Question 6.
Name three Deciduous trees.
Answer:
Arjun, Teak, Arnlaki are three deciduous trees.

Question 7.
Name three thorny plants.
Answer:
Cactus, Babul and Saguaro cactus are three thormy plants.

Question 8.
Name some animals which live in rain forests.
Answer:
Tapir, Gorilla, Chimpanzee, Okapi, Orangutam, Sumatran tigers live in rain forests.

Question 9.
What are the two main forests of West Bengal?
Answer:
The two main forests of West Bengal are forests of Sunderban and Dooars forest

Question 10.
What kinds of trees are observed in the Dooars and Terai forests?
Answer:
Trees like Sal, Gamhar, Odal, Khair, Sishu, Emblica are observed in the Dooars and Terai forests

Question 11.
Which plants are found in the slopes of high mountains of North Bengal?
Answer:
Rhododendran and Pine are found in the slopes of high mountains of North Bengal.

Question 12.
Which layer of forest is capable to synthesise maximum amount of food?
Answer:
The first layer of forest, canopy layeris capable to synthesise maximum amount of food.

Question 13.
Name sonic creatures which are permanent inhabitant of Herb layer?
Answer:
Mice, insects, snakes, wood turtles, toads and some species of birds are permanent inhabitant of Herb layer.

Question 14.
Which organisams live in the forest floor or last layer of forest?
Answer:
Countless earthworms, cockroaches, centipedes, snails and different microscopic organisms live in the forest floor of last layer of forest.

Question 15.
How much of total land area of earth is covered by forest?
Answer:
One-third of earth’s total land area remains covered by forest.

Question 16.
How much is natural forest?
Answer:
95% is natural forest.

Question 17.
How much is cultivated forest?
Answer:
5% is cultivated forest.

Question 18.
How much forest is in South America and Oceania?
Answer:
South America contains for 23% forest while Oceania contains only 5% forests.

Question 19.
Give an example of a devastating forest fire.
Answer:
In USA, in 1910, a devastating forest fire destroyed almost three million acres of forest.

Question 20.
Why the existence of one-horned rhinoceros is now jeopardised in the forests of North Bengal?
Answer:
Due to mushrooming of human habitat and gradual shrinkage of forests and wet grasslands suitable for rhino habitation.

Question 21.
What is mangrove forest?
Answer:
The plants community with respiratory roots, found in the southern tidal areas of West Bengal, form a type of forest popularly known as mangrove forest.

Question 22.
Name some mangrove tree.
Answer:
Sundari, Pasur, Keora, Garan are some mangrove trees.

Question 23.
Why some mangrove plants, give rise to stilt roots?
Answer:
Some mangroves give rise to plants sti It roots so that they cannot be extirpated from the soil due to the action of high and low tide.

Question 24.
What is the toxicity in the tissues of plants?
Answer:
Excess salts cause toxicity in the tissues of plants.

Question 25.
How mangrove plants try to eliminate the load of excess salts?
Answer:
Mangrove plants to eliminate the load of these salts partically by the lands plants eliminate salts by shedding of leaves.

Question 26.
Name some animals whose lives are threatened due to increase of salt in mangrove forest area.
Answer:
The lives of animals like Tiger, Estuarine Crocodile, River Terrapin are threatened due to increase of salt in mangrove forest area.

Question 27.
What are shells?
Answer:
Shells are actually the covering of marine animals which protects the soft body of the animal.

Question 28.
Where various marine organisms can be seen in the watery region above the continental reef?
Answer:
Here sponge and other invertebrate animals, small fishes, marine turtles, sea-cow, sea-horse and small marine shrimps can be seen.

Question 29.
Name some organisms found in the space created in between the highest water level in high tide and the lowest water level during low tide.
Answer:
The animals include lichens, algae, snils, mussels, star fishes, sea anemoones, crab etc.

Question 30.
What is kelp?
Answer:
Kelp is a king of marine algae.

Question 31.
Name some vertebrate animals found in depths on sea.
Answer:
Some vertebrate animals are — shark, hatchet fish and other marine fishes, whale.

Question 32.
Name some invertebrate animals found in depths of sea.
Answer:
Some invertebrate animals are jelly fish, sea anemone, shrimp, crab, squid, octopus, starfish, sea cucumber.

Question 33.
How the plants in the deep sea produce food?
Answer:
The plants in the deep sea produce food by photosynthesis.

Question 34.
What is lucifcrin and Iuciferase?
Answer:
Luciferin is a protein-bound pigment and Iuciferase is an enzyme.

Question 35.
Where majority of the bio-luminescent organisms can be seen?
Answer:
The majority of the bio-luminescent organisms can be seen at 200-1000 metre depth of the ocean,

Question 36.
How many Planktons arc there?
Answer:
There are two types of planktons—

• Phytoplankton and
• Zooplankton.

Question 37.
How sea-pen looks?
Answer:
Sea-pen looks like a pen made of duck feathers, it

Question 38.
How Dinoflagellates move?
Answer:
Dinoflagellates move with the help of flagella.

Question 39.
What are phytoplankton?
Answer:
Phytoplanktons are unicellular microscropic plants which live in the euphotic zone.

Question 40.
What are Zooplankton?
Answer:
Zoo plankton are mainly very small microscopic and non-microscopic animals which float on the upper layer of the ocean.

Question 41.
How many arms are there in octopus?
Answer:
There are eight arms in octopus.

Question 42.
Which octopus is the biggest octopus?
Answer:
The biggest octopus is the Giant octopus of the Pacific Ocean.

Question 43.
Which octopus is fatal for humans?
Answer:
The blue-ringed octopus can prove to be fetal for humans.

Question 44.
How octopus protects himself from enemies?
Answer:
When attacked, it sprays an ink-like substance from a g|and into body and flees making the water turbid.

Question 45.
How many arms squid has?
Answer:
The squid has ten arms — eight small ones near its head and two other big, long and fleshy ones.

Question 46.
How squid catches its prey?
Answer:
The squid catches its prey with suckers.

Question 47.
How squid fools its enemies?
Answer:
When attacked they flee by making a fool of its enemies by spraying a brounish fluid and making the water turbid.

Question 48.
Where Giant Squid lives? Flow long are they?
Answer:
The Giant Squid lives in the deeper parts of the Atlantic Ocean. They are generally 50¬60 feet long.

Question 49.
Is there hard bones in the body of a shark?
Answer:
The shark is not a fish made up of hard bones, their skeleton is made up of cartilage, which is softer than bones.

Question 50.
Which sharks are man-eaters?
Answer:
Few sharks like the Great White Shark, Hammer-headed shark are man eater.

Question 51.
Name some sharks which do not harm human-beeings.
Answer:
Big sharks, like Basking shark or whole shark, do not harm human beings.

Question 52.
How many arms has a star-fish?
Answer:
The star-fish has five arms.

Question 53.
How the star-fish moves?
Answer:
The star-fish moves with the help of the tube feet.

Question 54.
What is the favourite food of star-fish?
Answer:
Clams and mussels are the favourite food of star fish.

Question 55.
What causes ocean pollution?
Answer:
Pesticides, weedicides, chemical fertilisers, detergents, oil, sewage, plastic and different solid objects thrown in ocean causes ocean pollution.

Question 56.
Which desert is present in our country?
Answer:
Thar desert is present in our country.

Question 57.
Name some deserts which arc very cold at night?
Answer:
Gobi Desert in Asia, the desert in Antarctica are too cold at night.

Question 58.
What is called the ship of the desert?
Answer:
Camels are used mainly for travelling in the desert, so it is called the ship of the desert.

Question 59.
How many types of Camels are there?
Answer:
There are two types of camels—One-humped (Arabian Camel) apd two-humped (Bactrian camel).

Question 60.
How many days camel can survive without food in desert?
Answer:
Camel can survive without food for seven days.

Question 61.
What is the most poisonous snake in the deserts?
Answer:
Rattle snake is the most poisonous snake in the deserts.

Question 62.
What is Gerbil?
Answer:
Gerbil are small rat like animal living in desert.

Question 63.
Name some animals found in Thar desert.
Answer:
The animals found in Thar desert are – thorned tailed lizard, fox, camel, snake, vulture.

Question 64.
Name some types of plant that occur in the desert.
Answer:
Some plants are Answer: Cactus, Jashua plant, Saguaro cactus, Mesquite plant.

Question 65.
How much water Saguaro Cactus can store?
Answer:
Saguaro Cactus can store about six to eight ton water in their body.

Question 66.
How are Saguaro cactus useful?
Answer:
The desert travellers quench their thirst by collecting water from their expanded trunk. Their fruits are used to make jam. Their wood are also use for fuel.

Question 67.
Name some animals found in Sahara desert.
Answer:
Some animals found in Sahara desert are – porcupine, ostrich, hyena, fox, owl.

Question 68.
Name some types of plant that occur in the desert.
Answer:
Some plants are — cactus, jashua plant, saguaro cactus, mesaquite plant.

Question 69.
Name some animals found in Gobi desert.
Answer:
Snow leopard, wild sheep, Blue mountain pigeon are found in Gobi desert.

Question 70.
How do the fruits of the Saguaro cactus look like?
Answer:
The fruits of the Saguaro cactus look like a watermelon.

Question 71.
Name the largest bird of Thar desert?
Answer:
The largest bird of Thar desert is ‘Bustard’.

Question 72.
Who are Bushman?
Answer:
The people living in the Namib Desert of South-West Africa is known as Bushman.

Question 73.
What the people living in Kolahari Desert are called?
Answer:
The people living in Kalahari Desert are called San Bushman’.

Question 74.
What the tribes of Sahara Desert are called?
Answer:
The tribes of Sahara Desert are called Tuareg.

Question 75.
What are Pueblo?
Answer:
The Red Indians of Amercian Desert live together in stone-made house which are called Pueblo.

Question 76.
Name some tribes living in Thar Desert.
Answer:
Wardha, Bhil, Gadia-Lohar are some tribes living in Thar Desert.

Question 77.
Which year was announced by United Nations as the International year of Desert and Desertification?
Answer:
United Nations announced the year 2006 as the International year of Desert and Desertification.

Question 78.
What is the characteristic of biodiversity of Arctic Regions?
Ans:
The biodiversity of Arctic Regions are charcterised by the presence of aquatic mammals.

Question 79.
Name some significant animals and plants of Arctic Regions.
Answer:
The most significant animals are whale, seal, Sea Lion, Caribou, dog, dolphin, Polar Bears, birds like Arctic Tern and plants like moss, grass, lichen and birch.

Question 80.
What is Migration?
Answer:
Migration is the movement of an animal leaving from one region or habitat, to another.

Question 81.
How many types of fishes are found in the water of the Arctic Ocean?
Answer:
Almost 240 types of fishes are found in the water of the Arctic Ocean.

Question 82.
What are the people living in the Arctic Polar region known as?
Answer:
The people who settle permanently in the Arctic Polar region are popularly known as “Eskimo’.

Question 83.
What the snow house made by Eskimos called?
Answer:
The snow house is called ‘Igloo’.

Question 84.
What the Eskimos eat?
Answer:
Their main foods are seals, salmons and cod fishes. They hunt and eat flesh of ducks, hares, polar fox, polar bear and whales.

Question 85.
What is the indispensable part of the life of Eskimos?
Answer:
The indispensable part of the life of Eskimos are dogs.

Question 86.
What is the largest variety of penguin?
Answer:
The largest variety of penguin is the Emperor Penguin.

Question 87.
Name one of the least polluted places on the earth.
Answer:
The least polluted places on the earth is Anterctica.

Question 88.
What is IUCN?
Answer:
IUCN (International Union for the Conservation of Nature and Natural Resources) is an international agency which publish the list of names of endangered animals.

Question 89.
Name five endangered animals of India.
Answer:
Royal Bengal Tiger, estuarine crocodile, Asiatic lion, vulture.

Question 90.
Name two Vulture rehabiliation centers.
Answer:
Pinjar of Haryana and Rajabhat khaoa of North Bengal.

Question 91.
What is the state animal of West Bengal?
Answer:
A wild cat – popularty known as Fishing Cat or Baghrole.

Question 92.
Which is the world’s first dolphin sanctuary? When was it set up?
Answer:
The world’s first dolphin sanctuary, Vikramshila Gangetic Dolphin Sanctuary has been set up in 1991.

Question 93.
How is the eyesight of Rhinoceros?
Answer:
The eyesight of Rhinoceros is weak.

Question 94.
What is the rhinoceros horn made up of?
Answer:
It is made up of keratin. Ceratin is a kind of protein which makes nails and hairs.

Question 95.
When the horn of rhinoceros emerges?
Answer:
The horn of rhinoceros emerges slowly after the age of 6 years.

Question 96.
What is the curious habit of rhinoceros?
Answer:
The rhinoceros has the curious habit of defecating at the same place.

Question 97.
How many years the one-horncd rhinoceros survives in natural condition?
Answer:
It survives for 35-45 years.

Question 98.
Name two national parks of West Bengal where one-horned rhinoceros could be seen?
Answer:
Jaldapare and Gorumara.

Question 97.
How many years the one-horned rhinoceros survive in natural condition?
Answer:
It survives for 35-45 years.

Question 98.
Name two national parks of West Bengal where one-horned rhinoceros could be seen?
Answer:
Jaidapare and Gorumara.

Short Questions & Answers : (2 marks for each question)

Question 1.
How are Penguins useful?
Answer:
Factories manufacture soaps and fuels from penguin oil. It is also used to make medicine. Penguin feathers are used for making clothes, hats, shoes and bags.

Question 2.
How are Saguaro cactus useful?
Answer:
The desert travellers quench their thirst by collecting water from their expanded trunk. Their fruits are used to make jam. Their wood are also used to make strong rope and in building of houses.

Question 3.
What is stored in the humps of the camel?
Answer:
The hump of the canel is reservoir of fatty body. They collect their energy from this tissue and can live without food for seven days.

Question 4.
What is Algal Bloom?
Answer:
When the nutrients present in chemical fertilisers and sewage mix with ocean water, the number of the phytoplanktons increases enormously and cover the ocean surface. This situation is termed as Algal Bloom.

Question 5.
How star-fish catches its prey?
Answer:
The star-fishes catch their prey by taking in and ejecting out the water through the tube feed. A temporary vacuem is created for taking in the water. As a result the prey gets stuck to the tube feet.

Question 6.
What is ocean foam?
Answer:
A close relative of the squid is the cattle fish. When it rots near the sea side, this calcium-containing hard object can easily be collected. This object is sold under the name of Ocean foam.

Question 7.
What is biolumincscence?
Answer:
Even thought the sunlight does not penetrate into the depths of the ocean, a light of the different kind without heat is visible. This is termed as bioluminescence.

Question 8.
What are bioluminescent organisms?
Answer:
Some organisms are found deep in the ocean who can produce light in their bodies by chemical reaction. These organisms are termed as bio-luminescent organisms.

Question 9.
Why the incidences of infestation of leopards in the human habitat adjoining forests and the tea gardens of North Bengal are frequently occuring?
Answer:
Due to shortage of forest area feeding habit of leopard has changed. There is crisis of natural prey so they are becoming more dependent on capturing goat, cattles, ducks etc from the

Short Questions & Answers : (2 marks for each question)

Question 1.
How are Penguins useful?
Answer:
Factories manufacture soaps and fuels from penguin oil. It is also used to make medicine. Penguin feathers are used for making clothes, hats, shoes and bags.

Question 2.
How are Saguaro cactus useful?
Answer:
The desert travellers quench their thirst by collecting water from their expanded trunk. Their fruits are used to make jam. Their wood are also used to make strong rope and in building of houses.

Question 3.
What is stored in the humps of the camel?
Answer:
The hump of the canel is reservoir of fatty body. They collect their energy from this tissue and can live without food for seven days.

Question 4.
What is Algal Bloom?
Answer:
When the nutrients present in chemical fertilisers and sewage mix with ocean water, the number of the phytoplanktons increases enormously and cover the ocean surface. This situation is termed as Algal Bloom.

Question 5.
How star-fish catches its prey?
Answer:
The star-fishes catch their prey by taking in and ejecting out the water through the tube feed. A temporary vacuem is created for taking in the water. As a result the prey gets stuck to the tube feet.

Question 6.
What is ocean foam?
Answer:
A close relative of the squid is the cattle fish. When it rots near the sea side, this calcium containing hard object can easily be collected. This object is sold under the name of Ocean foam.

Question 7.
What is biolumincscence?
Answer:
Even thought the sunlight does not penetrate into the depths of the ocean, a light of the different kind without heat is visible. This is termed as bioluminescenee.

Question 8.
What are bioluminesccnt organisms?
Answer:
Some organisms are found deep in the ocean who can produce light in their bodies by chemical reaction. These organisms are termed as bio-luminescent organisms.

Question 9.
Why the incidences of infestation of leopards in the human habitat adjoining forests and the tea gardens of North Bengal are frequently occuring?
Answer:
Due to shortage of forest area feeding habit of leopard has changed. There is crisis of natural prey so they are becoming more dependent on capturing goat, cattles, ducks etc from the
border area villages of forest.

Question 10.
Why there is crisis of liuniari-elephant conflict in North Bengal forest?
Answer:
This occurs due to mushrooming of human habitat and construction of Railway track on the corridor of elephants. Moreover elephants roam over a large area while harvesting of maize at the onset of rainy season and harvesting of paddy at the onset of winter season. These are responsible for human-elephant conflict.

Long Questions & Answers : (3 marks for each question)

Question 1.
What benefit man get from a forest?
Answer:

• Forsest control temperature of earth and its water cycle.
• It controls erosion of soil and flood.
• Forest produces wood for furniture and different industries.
• It controls water-level under the soil.
• It is the source of fuel.
• It is the source of different drugs for dreadful diseases.

Question 2.
Explain briefly the structure of an ideal forest.
Answer:
An ideal forest has five layers —

i) First layer is the canopy cover formed by the leafy top branches of the tallest trees in the forest. It forms a dense closed cover that does not let in any sunlight. It is generally formed at a height above 30 metres.

ii) Some trees are seen below the Canopy layer which try’ to lengthen deep growing themselves to touch the canopy layer. This second lay er constitutes of short species of trees, shrubs, young plants and soft-stemmed plants.

iii) The third layer is formed by young trees, mature shrubs and thorny bushes. Small animals of the forest use this layer for the source of food, shelter and protection.

iv) The fourth layer is of Herbs. This layer of forest consists of plants like sproutings, ferns, grasses and several types of weed. Mice, insects, snakes, wood turtles, toads and many other creatures, including some species of birds, are permanent inhabitants of this layer.

v) The forest floor is the last layer of a well-formed forest. It is an incredible combination of dead leaves, fallen patels, rotting fruits, short twings, bird feathers, fur and faeces of animals and animal decaying matters, Countless earth worms, cockroaches, centipedes, snails and different microscopic organisms live in this layer.

Question 3.
What are the natures of different types of forest found in different parts of the world?
Answer:
Forests are distributed unevently across the globe. Only one-third of earth’s total land area remains covered by forest, of which 95% is natural forest. And the rest 5% is cultivated forest. South America accounts for 23% forest while Oceania contains only 5% forests. Ten countries in the world have no forest cover. And in another 64 countries forests cover less than 10% of the total land area.

Question 4.
What are Rain forests?
Answer:
Rain forests are featured by tall plants, warm weather and torrential rainfall. This type of forest is mostly observed along the equator (within a span of 10° above and below). In a tropical rain forest, the trees are so densely packed that it may take up to 10 minutes for rain to make its way through them and reach the ground.

Question 5.
How are Rainforests helpful to us?
Answer:

• Rainforests generate much of the earth’s atmospheric oxygen.
• They are responsible for forming rain by releasing moisture into the atmosphere, which returns to the ground as rain.
• Rainforests only parallel itself in stabilising the climate.
• This moderates the (low of rivers and prevents the recurrence of flooding.
• These rainforests are vital source of many life-saving medicines.
• Rain forest is the hebitat of different types of animals and birds. It is also the home of the colourful fishes.

Question 6.
Define the different factors which are responsible for forest fire.
Answer:
Different factors responsible for forest fire —

• Volcanic eruption may enhance the chance of contact of dry twigs or branches with any ignited object.
• Lighting strikes.
• Friction of bamboos swaying due to high wind.
• Sparks created by rolling stones if it comes in contact with highly inflammable leaf-strewn on the forest floor.
• Different human activities — smoking or cooking etc. inside the forest area.

Question 7.
What damage occurs due to Forest fire?
Answer:

• Fire damages forest, concentration of CO₂, in the air increases steadily and the concentration of O₂, decreases gradually. Consequently temperature of the environment increases.
• The chance of flood increases as a consequence of the fire.
• Due to burning of large trees, erosion of soil increases from the intensity of rain.
• Water bodies are polluted from the tons of ash that are run off with the first rains after the fire.
• Some animals are killed immediately if forest fires set in, others lose their shelter.

Question 8.
How forest can be conserved?
Answer:

• Preventing felling of trees in forest areas.
• Planting saplings and creating new forest areas.
• Reducing the chance of forest fire and control grazing.
• Cutting only trees after reaching proper age and planting trees of same species in such particular areas.
• Taking adequate measures to check the spread of disease of any tree in the forest.

Question 9.
Explain the crisis of forest of North Bengal.
Answer:

• Dhupi forest and Sai’or Teak forest are being artificially created at the cost of deforestation of natural forests.
• Natural forests shrink in size as compared to part days due to plantation of tea here and there.
• To establish human habit at end for construction of Railway track gradual shrinkage of forests are occuring.
• The existence of one-horned rhinoceros, leopard, elephant etc wild animals is now jeopardised in the forests of North Bengal due to shrinking of forest.

Question 10.
What crisis Mangrove forest is facing at present?
Answer:

• The plants become submerged twice under water during the time of high tide, so it becomes impossible to carry out breathing as soon as the minute pores are covered with mud.
• During the time of high tide the marine saline water enter inside the creeks directly. Plants of terrestrial lands cannot tolerate salts, excess salts cause toxicity in the tissues of plants.
• Some mangrove give rise to stilt roots so that they cannot be extirpated from the soil due to the action of high and low tide. Special measures are observed in these plants so that young plants can cling to the soil very firmly. As a consequence of ail thse several trees have started decreasing in significant numbers.

Question 11.
What are planktons? How many types of planktons are there?
Answer:
Planktons are aquatic organisms, who do not have the ability to swim against the water current. They are important food source for big aquatic animals like fishes, whales.
Planktons are of two types —

• Phytoplankton : They can produce food with the help of sunlight. These unicellular microscopic plants live in the euphotic zone. Various marine organisms feed on them. Some example are — Diatoms, Dinoflagellates.
• Zooplankton : They float on the upper layer of the ocean. They cannot produce food by themselves and feed on other planktons.

Question 12.
What is Oasis?
Answer:
A little bit of rainfall in the desert accumulated into the layer of rocks. In the desert, when the layer of the rock breaks, the water comes out and create a pond. Surrounding this ponds the trees grow. This area is called Oasis of a desert. In Oasis it seems a little bit of life touches in the lifeless desert.

Question 13.
How do animals survive in the low’ temperatures of the Arctic?
Answer:
i) Hibernation : Many terrestrial animals, of Arctic regions adopt hibernations as soon as the severe cold sets in. During this phase they do not move at all. Body temperature goes down. Heart beat and the rate of breathing slows down. Some hibernating animals even store food in their burrows.

ii) Migration: Many animals of Arctic region like birds, reindeer etc migrate from colder regions to warmer places to find food or to give birth the their young ones. For example, Arctic Tern reaches Antarctica from Arctic Regions by flying 11,000 miles.

Question 14.
What are the causes of niassacare of vulture?
Answer:
i) Diclofenac was administered in the body of cattles for allevitating different diseases. The residue of this drug was left in the carcasses. This diclofenac destroyed the normal functioning of the kidneys of vultures. This led to the massacare of vultures. Another cause — vultures do not get their adequate food.

Question 15.
What are the crises of Fishing Cat?
Answer:
Large metal roads, housing projects and shopping malls are being constructed at the expense of bushy jungles or wetlands having khar, reed or hogla plants. Factories, and brick fields are also being constructed here and there. As a result habitat and source of natural food of the fishing cats are decreasing day by day. So they are being compelled to intrude into human habitat in search of ducks and hens. They are also being killed by humans.

Question 16.
What are the crises of Gangetic dolphin?
Answer:
The existence of the dolphins is endangered due to various activities of human beings. The depth of water in the river is decreasing due to the construction of dams and other reasons. Emergence of sandbars devide the river in small parts.

This hinders the movement of the Gangetic Dolphins. The dolphins live in such a region ofthe Ganges that is surrounded by densely populated localities. Pollution of river water emerges as a major problem. The dolphins are endangered due to lack of food. Sometimes they die being entrapped in fishing nets.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.2 Force Active Without Contract offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.2 Question Answer – Force Active Without Contract

Multiple Choice Questions Answers : (1 mark for each question)

Question 1.
What is the name of attractive force which act between two bodies in the universe-
i) nuclear force
ii) gravitational force
iii) magnetic force
iv) coulomb attractive force
Answer:
ii) gravitational force

Question 2.
The value of gravitational acceleration-
i) increases as height increase from the earth
ii) decreases as height increase from the earth
iii) remains constant
iv) none of the above
Answer:
i) increases as height increase from the earth

Question 3.
In which region of earth the weight of a body is slightly greater?
i) at equator
ii) tropic of cancer/tropic of capricorn
iii) at polar region
iv) none of the above
Answer:
iii) at polar region

Question 4.
Gravitation is a which type of force?
i) repulsive force
ii) attractive or repulsive force
iii) attractive force
iv) not a force
Answer:
iii) attractive force

Question 5.
The force involved in falling of an apple from a tree is known as-
i) magnetic force
ii) electrostatic force
iii) contact force
iv) gravitational force
Answer:
iv) gravitational force

Question 6.
Which of the following is an example of a non-contact force-
i) the force exerted by us to lift a bucket
ii) hit a cricket ball for runs
iii) the force exerted by magnet
iv) push a stationary car
Answer:
ii) hit a cricket ball for runs

Question 7.
In Newton’s equation F = _____.
i) universal gravitational constant
ii) distance between the two particles
iii) gravitational force
iv) masses of two point object
Answer:
iii) gravitational force

Question 8.
Mass of a proton is-
i) 9.11 10²⁸ gm
ii) 1.675 10²⁴ gm
iii) 1.6725 10²⁴ gm
Answer:
iii) 1.6725 10²⁴ gm

Question 9.
An atom is usually electrically neutral because-
i) proton and neuton have same number of charges
ii) neutron and electron have same number of charges
iii) proton and electron have same number of charges
iv) none of the above
Answer:
iii) proton and electron have same number of charges

Question 10.
Metals are good conductor of electricity because-
i) metals are hard
ii) metals have large number of free electrons
iii) metals have many protons.
iv) none of the above
Answer:
ii) metals have large number of free electrons

Question 11.
Two types of charges were named by-
i) Franklin
ii) Coulomb
iii) Faraday
iv) Archimedes
Answer:
i) Franklin

Question 12.
If electron increases in a body then it would be-
i) negatively charged
ii) positively charged
iii) charge free
iv) none of the above
Answer:
i) negatively charged

Question 13.
It is safe to do electrical work standing on a woolen stool because it is
i) good conductor
ii) preventive
iii) bad conductor
iv) none of the above
Answer:
ii) preventive

Question 14.
Which particle revolves around the centre of atom-
i) proton
ii) neutron
iii) electron
iv) none of the above
Answer:
iii) electron

Question 15.
A semi conductor material is-
i) silicon
ii) glass
iii) copper
iv) none of the above
Answer:
i) silicon

Question 16.
Which one is good conductor –
i) silicon
ii) graphite
iii) cbonite
iv) none of the above
Answer:
ii) graphite

State whetherTrue or False : (1 mark for each question)

1. G is called ‘Universal gravitational constant’.
2. In a vacuum place a gold coin will fall faster than a feather.
3. Similar charges attracts each other.
4. CGS unit of force is Dyne.
5. The force with which sun attracts an object near it is called gravitational force.
6. The force with which earth attracts an object near it is called gravitational force.
7. If dry hair is combed static electricity is produced.
8. The negative charged particle of atom is proton.
9. The positive charged particle of atom, is proton.
10. CGS unit of force is Newton.
11. The negative and positive charged particles of an atom has same numerical value.
12. When two materials are rubbed against each other one becomes positively and the other becomes negatively charged.
13. G is called acceleration due to gravity.
14. Hydrogen has no neutron.
15. When an atom loses onc or more electron(s) it becomes positively charged.
16. An atom consists of four types of particles.
Answer:
1. true
2. false
3. false
4. true
5. false
6. true
7. true
8. false
9. true
10. false
11. true
12. true
13. false
14. true
15. truc
16. false

Fill in the blanks : (1 mark for each question)

1. Galileo established three laws for _______ objects.
2. Of all metals _____ is the best conductor of electricity.
3. Static electricity can be produced by _____.
4. Neutron is not present in the nucleus of ____ atom.
5. Minimum velocity to overcome gravitational pull of the earth is –
6. Same kind of electrical charges ______.
7. In the core of atom lies _____ and _____.
8. Earth pulls every object towards itself through _______ force.
9. Average radius of earth ________.
10. Most metals conduct electricity because they have enough _____ available in them.
11. Force = ______ × ______.
12. _____ is called Universal gravitational constant.
13. The force of gravity on unit mass is numerically equal to the ______ due to gravity.
14. When an object is thrown upward, its speed ______ with aititude.
15. French scientist ______ invented a formula to calculate the force exerted between the two charged particles.
16. If glass is rubbed with silk, glass becomes ____ charged and silk becomes ______ charged.
17. The centre of the atom is called ______.
18. Electrons carry ______ charges.
Answer:
1. free-falling
2. silver
3. rubbing
4. Hydrogen.
5. 11.2 km / sec
6. repel
7. Proton, Neutron
8. gravitational
9. 6370 km
10. free electrons
11. Mass, acceleration
12. G
13. acceleration
14. decreases
15. Charles Augustin de Coulomb
16. positively, negatively
17. Nucleus
18. ‘negative

Match the following : ( 1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Gràitation is a kind of	i) is different in different places.
b) SI unit of weight is	ii) an applied force
c) In the centre of earth	iii) it falls same speed.
d) Va’ne of acceleration due to gravity	iv)  11.2 km / sec
e) Velocity of an object changes due to	v) is a kind of universal constant.
f) If an object falls without any hindrance	vi) force
g) Minimum velocity to overcome gravitational pull	vii) weight of object becomes zero.
h) Universal gravitational constant	viii) Newton.

Answer:
a) Gravitation is a kind of force
b) SI unit of weight is Newton.
c) In the centre of earth weight of object becomes zero.
d) Value of acceleration due to gravity is different in different places.
e) Velocity of an object changes due to an applied force.
f) If an object falls without any hindrance it falls at same speed.
g) Minimum velocity to overcome gravitational pull 11 \cdot 2 km / sec.
h) Universal gravitational constant is a kind of universal constant.

b) Match the column A with column B.

Column A	Column B
a) Eleetron carries	i) attract each other
b) Like chăges	ii) weight of objects
c) Unlike charges	iii) attract each other
d) Aristotle was a famous philosopher	iv) gravitational force
e) Any two objects of this universe	v) with increasing time of fall
f) Spring balance measures	vi) repel each other
g) The earth pulls all objects with	vii) negative charges
h) Speed of a free-falling body increases	viii) of Greece

Answer:
a) Electron carries negative charges.
b) Like charges repel each other.
c) Unlike charges attract each other.
d) Aristotle was a famous philosopher of Greece.
e) Any two objects of this universe attract each other.
f) Spring balance measures weight of objects.
g) The earth pulls all objects with gravitational force.
h) Speed of a free-falling body increases with increasing time of fall.

Very Short Questions Answers : (1 mark for each question)

Question 1.
Due to which force all objects fall towards earth?
Answer:
Due to gravitational force all objects fall towards earth.

Question 2.
With what force one object attracts another object?
Answer:
With universal gravitation one object attracts another object.

Question 3.
What are the CGS and SI unit of measuring force?
Answer:
The CGS unit is dyne and SI unit is newton of measuring force.

Question 4.
What like charges do?
Answer:
Like charges repel each other.

Question 5.
What unlike charges do?
Answer:
Unlike charges attract each other.

Question 6.
What is produced by rubbing two materials?
Answer:
Charge is produced by rubbing two materials.

Question 7.
By what unit electric charge is measured?
Answer:
Electric charge is measured by coulomb.

Question 8.
What is the CGS unit of acceleration?
Answer:
Of acceleration CGS unit is cm / sec².

Question 9.
What is the SI unit of acceleration?
Answer:
Sl unit of acceleration is m / sec².

Question 10.
Who named the two charges positive and negative?
Answer:
Renowned scientist Benjamin Franklin gave name to two different charges.

Question 11.
If a glass rod is rubbed with silk what charges occur in which object?
Answer:
If a glass rod is rubbed with silk positive charge occurs in glass rod and negative charge occur in silk.

Question 12.
If an atom gains electron what charge it acquires?
Answer:
If atom gains electron is acquires negative charge.

Question 13.
If an atom releases electron of what charge it becomes?
Answer:
If an atom releases electron it becomes positive charge.

Question 14.
Name a neutral particle in atom?
Answer:
Neutron is a neutral particle in atom.

Question 15.
What type of charge is in proton?
Answer:
There is positive charge in proton.

Question 16.
What type of charge is in electron?
Answer:
There is negative charge in electron.

Question 17.
A fruit falling from tree is an example of which type of force?
Answer:
Gravetation force.

Question 18.
Water begins to flow towards the ground as soon as we open a tap. This happens due to which force?
Answer:
Force of gravity.

Question 19.
Who gave us preliminary idea about the nature of electrical charge?
Answer:
Benjamin Franklin.

Question 20.
What do you mean by free-falling object?
Answer:
When an object is falling freely towards earth due to gravitation, it is called a freefalling object.

Question 21.
What is the value of universal gravitational constant (G) in C.G.S. unit?
Answer:
6.67 * 10⁸

Question 22.
What is the value of universal gravitational constant (G) in S.I. unit?
Answer:
N^-m / kg².

Short Questions Answers : (2 marks for each question)

Question 1.
What is gravitation?
Answer:
Any two particles in the universe pull each other along a straight line joining them, this force is known as gravitation.

Question 2.
What is gravity?
Answer:
The force with which earth pulls everything towards its centre is called gravity. The earth’s gravitation is called gravity.

Question 3.
Why G is called ‘Universal gravitational constant’?
Answer:
The value of G remains same at each place and it is independent of nature of particles, temperature, medium etc. Therefore, it is universal constant and so G is knewn as universal gravitational constant.

Question 4.
What is weight of a body? How it is measured?
Answer:
The weight of a body is the force with which the earth attracts it. It is measured with spring balance.

Question 5.
What is escape velocity?
Answer:
The minimum velocity with which an object when thrown upwords from the earth’s surface overcomes gravitational pull of the earth and escapes the earth’s gravity, it is called escape velocity.

Question 6.
On what factors the attraction between two objects depend? Explain how they depend?
Answer:
The atraction between two objects depend on two factors-i) Mass of two objects : If mass of two objects increase then attraction between them also increase. ii) Distance between two objects: If distance between two objects increase attraction between them decrease.

Question 7.
What is contact force?
Answer:
Forces which act only when there is physical contact between two interacting objects are known as contact forces.

Question 8.
What are non contact force?
Answer:
Forces which can act without physical contact between objects are known as non contact forces.

Question 9.
Define electrostatic force.
Answer:
The force extracted by a charged body on another charged or uncharged body is known as electrostatic force.

Question 10.
Why atom is usually electrically neutral?
Answer:
Normally, an atom contains the same number of positively charged protons and negatively charged electrons. So an atom is usually electrically neutral.

Question 11.
How many types of electricity is there? Define.
Answer:
Electricity are of two types: i) Static electricity : When electric charge remains stationary, does not flow it is called static electricity. ii) Current electricity : When electric charges flow from one place to another it is called current electricity.

Question 12.
What Aristotle thought about free falling object?
Answer:
Aristotle thought that when allowed to fall freely from a certain height, a heavier object touches the ground before a lighter object.

Question 13.
What Galileo proved?
Answer:
Galileo proved that all material bodies irrespective of their weight, touch the ground at the same time when they are allowed to fall freely and simultaneously from the same height.

Long Questions Answers : (3 marks for each question)

Question 1.
What are the laws of electrostatic attraction and repulsion?
Answer:
a) Two negatively charged objects repel each other.
b) Two positively charged objects also repel each other.
c) A positively charged object attracts a negatively charged object.

Question 2.
What is triboelectric series?
Answer:
Some materials are arranged in a series which exchange large amounts of charges when they are rubbed against each other. The one higher up in the order will lose electrons readily and acquire a positive charge and the one lower down the order will gain electrons and get negatively charged. This series is called triboelectric series.

Question 3.
A truck transporting petrol has a metal chain dangling to the ground. Explain the reason.
Answer:
The tyres of the truck moving on the ground, due to friction acquire the negative charge (due to the movement of electrons from the ground to the tyres). The metal body of the truck near the tyres becomes positively charged by electrostatic induction. The negative charge on the tyre and the positive charge on the metal body may cause sparkling which can ignite the petrol and cause a fire. To avoid it, the truck has a metal chain on its body dangling to the ground so that the positive charge on its metal body gets neutralised by the electrons coming from the ground through the metal chain.

Question 4.
What is free falling object? State the three laws for free falling objects of Galileo.
Answer:
When an object is falling freely on earth due to gravitation, it is called free falling object.
The three laws for free falling objects established by Galleo are-

1. When objects at rest are allowed to fall freely from a certain height they fall down with same speed.
2. Speed of free falling body increases with the increase of time of fall.
3. Distance increases with the time of fall.

Question 5.
Write down mass and charge of proton, neutron and electron.
Answer:

Particles	mass	charge
proton	1.6725 × 1024	+ 4.8 × 10-10 e.s.u or,
neutron	1.6750 × 1024	+ 1.6 × 10-19 coulomb neutral
electron	9.1 × 1028	– 4.8 × 10-10 e.s.u – 1.6 × 10-19 coulomb

Question 6.
We have seen that bits of paper got attracted to a plastic comb wihich had got charged by rubbing it against dry hair, explain why it happen?
Answer:
Whenever two bodies are rubbed against each other some of the free electrons move from one body to another. The body which loses electrons gets a positive charge whereas the other body which gains electons (lost by the first body) acquires a negative charge. The static electricity produced in the comb by rubbing with hair, attracts bits of paper.

Question 7.
With an experiment proof that like charges repel.
Answer:
Rub a glass rod with silk. Suspend it freely with a thread. Rub another glass rod with silk. and bring it close to the suspended glass rod. It will be observed that the suspended glass rod gets repelled and moves away. As same charge is produced in the two glass rod they move apart. This experement proves that like charges repel.

Question 8.
Write Coulomb’s law and explain it.
Answer:
The force between two charged particles, regarded as point charges Q₁ and Q₂, a distance apart, is proportional to the product of the charges and inversely proportional to the square of the distance between them.
The formula is, F = k
Where Q₁, Q₂ represent the amount of charge of the two particles, ‘r’ is the distance between them and ‘ F ‘ is electrostatic force of attraction or repulsion. acting between them. The value of k depends upon the intervening medium between the charged particles.

Question 9.
From electrical point of view explain conductors and non-conductors.
Answer:
From the electrical point of view, most substances can be classified as conductors are and non-conductors of electricity. Conductors are substances that easily allow electric current to flow through them. Most metals conduct electricity because they have enough free electrons available in their crystal lattice. Non-conductors or insulators are substances that do not allow electric current to flow through them. Some examples of insulators or non-conductors of electricity are glass, ebonite, plastic, silk and wool. They do not conduct electricity because they do not have free electrons.

Question 10.
If charge of two particles are increased two times but the distance between them remains same than state what difference will occur in the attraction of two particles.
Answer:

∴ In second case the force of attraction would be 4 times greater then the first case.

Question 11.
Define charging by friction. Give example.
Answer:
Whenever two bodies are rubbed against each other, some of the free electrons move from one body to another. The body which loses electrons gets a positive charge whereas the other body which gains electrons acquires a negative charge.
Example : if a glass rod and a silk cloth are rubbed against each other, the glass rod loses electrons to the silk cloth. The glass rod, therefore gets positively charged and the silk cloth gets negatively charged.

Question 12.
Define charging by conduction. Give example.
Answer:
When an uncharged conductor is touched with a charged conductor. then the uncharged coductor gets charged and the process is called charging by conduction
Example : If a chargeless thermocol ball is touched with a positively charged glass rod, the ball becomes positively charged by conduction.

Question 13.
Define charging by induction. Give example.
Answer:
During charging by induction, no physical contact is made between the uncharged and the charged bodies. A charged body is brought very close to (but not touched with it) an uncharged body, and then the nearer end of the uncharged body acquires a charge which is of opposite nature to that of the charged body. The charges so produced on the uncharged conductor are called induced charges.

Question 14.
Describe the atomic structure.
Answer:
a) An atom consists of three kinds of particles that is, electrons (negatively charged particles), protons (positively charged particles) and neutrons (neutral particles). These are called sub-atomic particles.
b) Normally, an atom contains the same number of positively charged protons and negatively charged electrons. So an atom is ustally electrically neutral:
c) Protons and neutrons together form the core of the atom called the nucleus, which is presant at the centre. Electrons revolve around the nucleus in definite paths called orbits or shells.
d) The electrons in the outer orbits which are away from the nuclers are called free electrons because they can break loose and move about freely inside a suibstance. These free electrons act as charge carriers.
e) If a body gains electrons, it gets negatively charged, and if a body loses electrons, it gets positively charged. In both the cases, the bodies act as charged bodies.

Mathematical Problems : (3 marks for each question)

Question 1.
Mass of an object is 10 g. Find out its weight?
Answer:
Weight = mass × acceleration due to gravity
= 10 × 980 dyne = 9800 dync

Question 2.
Find out the value of force with which 5 kg mass object is pulled by earth?
Answer:
Earth’s gravity on 5 kg mass
= 5 × 9.81 Newton
= 49.05 Newton

Question 3.
Mass of one object remains same, but of another object mass is increased 3 times than before and their distance is also increased three times. Then will the gravitational force increase or decrease?
Answer:
The new gravitational pull will be multiple = multiple then before

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.1 Nature of Matter offer valuable context and analysis.

WBBSE Class 8 Science Chapter 2.1 Question Answer – Nature of Matter

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Lightest metal-
i) lithium
ii) hydrogen
iii) sodium
iv) calcium
Answer:
i) Lithium

Question 2.
An electro-positive non-metal is-
i) hydrogen
ii) sodium
iii) graphite
iv) diamond
Answer:
i) Hydrogen

Question 3.
Which of the following liquids has less boiling point?
i) water
ii) alcohol
iii) ether
iv) chloroform
Answer:
iii) ether

Question 4.
Which of these elements has highest density?
i) iron
ii) copper
iii) mercury
iv) gold
Answer:
iii) mercury

Question 5.
Which of the following gas is colourless-
i) nitrogen dioxide
ii) hydrogen
iii) hydrogen sulphide
iv) chlorine
Answer:
ii) hydrogen

Question 6.
Which of the following is magnetic element?
i) copper
ii) gold
iii) diamond
iv) cobalt
Answer:
iv) cobalt

Question 7.
Which of the following is crystalline substance-
i) sugar
ii) blue vitriol
iii) camphor
iv) diamond
Answer:
iii) camphor

Question 8.
Which of the following is conductor of electricity?
i) diamond
ii) sulphur
iii) arsenic
iv) gas carbon
Answer:
iv) gas carbon

Question 9.
Which of the following elements does not produce hydrogen gas by reaction?
i) iron
ii) calcium
iii) zink
iv) copper
Answer:
iv) copper

Question 10.
Which of the following is not metaloid?
i) Arsenic
ii) Antimony
iii) Sulphur
iv) Bismath
Answer:
iii) Sulphur

Question 11.
Sulphur is dissolved in-
i) chloroform
ii) carbon dioxide
iii) water
iv) mercury
Answer:
ii) carbon dioxide

Question 12.
Which of the following has lowest freezing point-
i) water
ii) mercury
iii) both of them
iv) it cannot be said
Answer:
ii) mercury

Question 13.
Which of the metal is most reactive-
i) Magnesium
ii) Sodium
iii) iron
iv) copper
Answer:
iv) copper

Question 14.
Which of the following is physical change-
i) rust on iron
ii) electrolysis of water
iii) melting of ice
iv) burning of paper
Answer:
iii) melting of ice

Question 15.
Which of the following is chemical change-
i) melting of iceberg
ii) boiling of water
iii) pouring of water on lime stone
iv) none of the above
Answer:
iii) pouring of water on lime stone

Question 16.
Powder of chalk and powder of sugar can be separated by-
i) physical property
ii) solubility in water
iii) by magnet
iv) by smelling
Answer:
ii) solubility in water

Question 17.
Which of the following is not a metal?
i) sulphur
ii) diamond
iii) graphite
iv) all of the above
Answer:
iv) all of the above

Question 18.
Which of the following is not soluble in water?
i) sugar
ii) salt
iii) chalk powder
iv) sugar-candy
Answer:
iii) chalk powder

Question 19.
A hard non-metal is-
i) graphite
ii) iodine
iii) diamond
iv) all of the above
Answer:
iv) all of the above

Question 20.
Which of the following is used in photography film?
i) sodium
ii) silver
iii) carbon
iv) hydrogen
Answer:
ii) silver

State whether True or False : (1 mark for each question)

1) Napthaline does not have liquid state.
2) Temperature changes when a liquid boils.
3) SO₂ has a smell like burnt out gunpowder.
4) Iron is a light metal.
5) Sulphur is soluble in carbon tetrachloride.
6) Alcohol mix in water.
7) Br₂ is colourless.
8) Blue vitriol is a crystalline substance.
9) Silver is a non-magnetic substance.
10) Water is an organic solvent.
11) Smell of Ammonium is like burnt out gun power.
12) Metals are fexible.
13) Rusting is a physical change.
14) All metals does not react with acids and produce H₂ gas.
15) Mercury is hard substance, so it is a metal.
16) Though mercury is liquid, it is a metal.
17) Graphite is a bad-conductor as it a non-metal.
18) Cystalline iodine is a non-bright substance.
Answer:
1) true
2) false
3) true
4) false
5) true
6) true
7) false
8) true
9) true
10) false
11) false
12) true
13) false
14) true
15) fale
16) true
17) false
18) false

Fill in the blanks : (1 mark for each question)

1) We can ______ substances by touching.
2) Nitrogen dioxide is ______ in colour.
3) Some substances undergo chemical changes on heating and are _________ into new substances.
4) Water is a _________ substance.
5) Melting point of ice is ________.
6) ______ is a volatile substance.
7) If pieces of zinc is immersed in dilute sulphuric acid _________ gas is produced.
8) ______ metal is used to make cooking utensils.
9) presence of __________ metalloid pollutes water.
10) In nature ____________ element is present in large amount.
11) _____ powder is used in making matchstick.
12) Reaction of iron and CuSO₄ produces Ferrous Sulphate and _____.
13) Bismath is a ______.
14) _______ is used in making electric wire.
15) Put appropriate symbol in following blanks :
i) Ca + H₂ O → Ca(OH)₂ + Ca ______
ii) Fe + H₂ O → FeO₃ + ______
iii) Zn + ______ → ZnSO₄ + H₂
Answer:
1) identify
2) brown
3) transformed
4) liquid
5) 0° C
6 ) ammonium chloride
7) Hydrogen
8) Aluminium
9) Arsenic
10) Oxygen
11) Phosphorus
12) Copper,
13) metalloid,
14) Copper
15) i) H₂
ii) H₂
iii) H₂ SO₄

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) Smell of a substance is	i) red
b) Chemical reaction	ii) non-metal
c) Ammonium chloride is a	iii) metal
d) In fixed pressure boiling point is	iv) it is good conductor of heat and electricity
e) Smell of SO2 gas is like	v) a physical property
f) Colour of Bromine is	vi) Hydrogen gas
g) Graphite is a	vii) a definite temperature
h) Gold is a	viii) changes atonic structure of a substance
i) Though graphite	ix) burnt gun power
j) Reaction of metal and acid produces	x) valatile substance.

Answer:
a) Sinell of a substance is a physical property.
b) Chemical reaction changes atomic structure of a substance.
c) Ammonium chloride is a volatile substance.
d) In fixed pressure boiling point is a definite temperature.
e) Smell of SO₂ gas is like burnt gun powder.
f) Colour of Bromine is red.
g) Graphite is a non-metal.
h) Gold is a metal.
i) Though graphite is a non-metal but it is good conductor of heat and electricity.
j) Reaction of metal and acid produces Hydrogen gas.

b) Match the column A with column B.

Column A	Column B
a) In physical change	i) is not soluble in kerosene
b) During the change of state	ii) blue
c) Ether is a	iii) is brown
d) Hydrogen	iv) is a magnetic substance
e) Sugar	v) light yellow coloured hard substance
f) Colour of blue vitriol is	vi) greenish yellow coloured gas
g) Nickel	vii) only outer structure change
h) Colour of NO2 gas	viii) is a odourless gas
i) Sulphur is	ix) temperature does not change.
j) Chlorine is a	x) volatile substance

Answer:
a) In Physical change only outer structure change.
b) During the change of state, temperature does not change.
c) Ether is a volatile substance.
d) Hydrogen is a odourless gas.
e) Sugar is not soluble in kerosene:
f) Colour of blue vitriol is blue.
g) Nickel is a magnetic substance.
h) Colour of NO₂ gas is brown.
i) Sulphur is light yellow coloured hard substance.
j) Chlorine is a greenish yellow coloured gas.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is the sign of gold?
Answer:
Sign of gold is Au.

Question 2.
What is the colour of chlorine gas?
Answer:
Greenish yellow is the colour of chlorine gas.

Question 3.
What is the boiling point of :thyl alcohol?
Answer:
Boiling point of ethyl alcohol is 78° C.

Question 4.
Give an example of physical property.
Answer:
smell is an example of physical property.

Question 5.
Give an example of chemical property.
Answer:
Reaction with acid is an example of chemical property.

Question 6.
Give an example of odourless liquid.
Answer:
Water is oderiess liquid.

Question 7.
What is smell of ammonium gas?
Answer:
Smell of ammonium gas is pungent.

Question 8.
Write the symbol of hydrochloric acid.
Answer:
Symbl of hydrochloric acid is HCl.

Question 9.
Write the symbol of zinc sulphate.
Answer:
Symbol of zink sulphateZnSO₄.

Question 10.
Write the symbel of marbel stone.
Answer:
S₂ mbol of marbel stone – CaCO₃.

Question 11.
Give an examples of two magnetic elements.
Answer:
Two magnetic elements Iron and Nickel

Question 12.
Name two crystalline elements.
Answer:
Two crystalline elements Sugar, Sodium Chloride.

Question 13.
Name two non-crystalline elements.
Answer:
Two non-crystalline elements Wax, Camphor.

Question 14.
What type of smell has H₂ S ?
Answer:
Like rotten egg.

Question 15.
Write two names of organic solvent.
Answer:
Two organic solvents Carbondi sulphide, Chloroform.

Question 16.
What is the colour of Nitrogen dioxide?
Answer:
Colour of Nitrogen dioxide Brown.

Question 17.
What will happen if water is powred on quick lime?
Answer:
Quick lime will form with excessive heat.

Question 18.
Write name of two metals which reacts with acid.
Answer:
Sodium and Magnesium reacts with acid.

Question 19.
Write a name of liquid metal.
Answer:
Mercury is liquid metal.

Question 20.
Write a name of liquid non-metal.
Answer:
Bromine is liquid non-metal.

Question 21.
Write name of two metals which have low melting point.
Answer:
Gallium and calsium.

Question 22.
Write a name of light metal.
Answer:
Aluminium.

Question 23.
What is the lightest element?
Answer:
Hydrogen.

Question 24.
Write name of two inactive elements.
Answer:
Helium, Neon are two inactive slements.

Question 25.
Which gas is present in large quantity in atmosphere?
Answer:
Nitrogen.

Question 26.
What elements are present in water?
Answer:
Hydrogen and oxygen.

Question 27.
Which metal is the highest conductor of electricity?
Answer:
Silver is the highest conductor of electricity.

Question 28.
Which ions control the functioning of heart?
Answer:
Ca²⁺ and k⁺.

Question 29.
Write the name of element which is the main constituent of teeth and bones?
Answer:
Calcium.

Question 30.
What is mainly present in haemoglobin?
Answer:
Iron is mainly present in haemoglobin.

Question 31.
Write a name of metal iron which control the constraction of muscle.
Answer:
Mg²⁺.

Question 32.
Which ion plays an important function in the process of coagulation of blood.
Answer:
Calcium ion (Ca²⁺).

Question 33.
What are the two principal cations of our intracellular and extracellular body fluids?
Answer:
Na⁺and K⁺.

Question 34.
Name two proteins which play a vital role in muscle contraction.
Answer:
Actin and myosin play a vital role in muscle contraction.

Question 35.
Write an use of lead.
Answer:
Lead is used in making of battery.

Question 36.
What is the colour of red litmus.
Answer:
The colour of red litmus is red.

Question 37.
What is the colour of red litmus in base?
Answer:
Blue is the colour of red litmus in base.

Question 38.
Name the metals and non-metals present in toothpaste.
Answer:
Carbon, Hydrogen, Oxygen, Aluminium, Calcium.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is matter?
Answer:
All the materials in our surrounding are composed of matter. Matter has mass and volume which can be felt by our senses.

Question 2.
What are physical properties?
Answer:
Some properties of a substance, such as physical state, colour, odour, melting point, boiling point, magnetism, solubility etc. from which we can get an idea about the nature and external condition of the substance, are called the physical properties of substance.

Question 3.
What are chemical properties?
Answer:
The properties of a substance which decide its tendency and power to react with other substances are called its chemical properties.

Question 4.
Give example of chemical properties.
Answer:
On electrolysis, water gives hydrogen and oxygen. This is a chemical property of water. Zinc reacts with dilute sulphuric acid to produce hydrogen gas. This is a chemical property of zinc.

Question 5.
Water can exist in three states. What are they?
Answer :
Water can exist in three states. They are solid state : ice, liquid state : water, Gaseous state : water vapour.

Question 6.
Write name of some gas which have odour, mention how they smell.
Answer:
Ammonia → pungent-smelling. Hydrogen sulphide → rotten egg. Sulphurdi oxide → burnt gunpowder. Phosphin → rotten fish.

Question 7.
Write name of some colourful gas, write their colours.
Answer:
Nitrogen dioxide → brown. Chlorine → Greenish yellow. Iodine vapour → violet.

Question 8.
How could you seperate sugar powder and burnt out lime powder from its physical properties?
Answer:
Sugar powder makes a clear solution when mixed with water, but burnt out lime does not melt in water, it floats on water.

Question 9.
How could you seperate sugar powder from salt powder by to chemical properties?
Answer:
We could seperate them by giving heat. When heated sugar powder becomes brown first and then it becomes black. Whereas salt powder would not have any remarkable change when heated up.

Question 10.
What reaction will happen if dilute H₂ SO₄ is added to zinc powder?
Answer:
If dilute H₂ SO₄ is added to zinc powder it reacts and produces zinc sulphate salt and gas bubbles of hydrogen. Zn + H₂ SO₄ = ZnSO₄ + H₂

Question 11.
What would happen if water is poured on calcium oxide?
Answer:
If water is poured on calcium oxide a reaction will occur which would produce lot of heat and slaked lime will be produced.
CaO+H₂ O=Ca(OH)₂ + heat.

Question 12.
What is metalloid? Give example.
Answer:
Metailoids are chemical elements inter-mediate in properties between metals and nonmetals. Example: Arsenic, Antimone, Bismath.

Question 13.
What are magnetic elements? Give ex:mple.
Answer:
The substances which are attracted by magnet are called magnetic elements. For example : iron, nicel, cobalt.

Question 14.
What are metals?
Answer:
Metals are defined as elements that form positive ions by losing electrons. They contain 1-3 valence electrons. For example-sodium has 1 . copper has 2 and aluminium has 3 valence electrons.

Question 15.
What are non-metals?
Answer:
Non-metals are defined as clements that form negative ions by gaining electrons. They contain 4-7 valence electrons. For example, carbon has 4, nitrogen has 5, oxygen has 6 and chlorine has 7 valence electrons.

Long Questions & Answers : (3 marks for each question)

Question 1.
What would happen if magnesium wire is burnt in air?
Answer:
If magnesium wire is burnt in air it would burn with bright flame. Magnesium reacts with oxygen upon ignition and then continues to burn with a bright flame forming white powder of magnesium oxide. Magnesium will react with nitrogen and form magnesium nitrate.

2 Mg+O₂ = 2 MgO
3 Mg+N₂ = Mg₃ N₂

Question 2.
Though hydrogen is a gas it is placed in activity series why?
Answer:
Though hydrogen is a non-metal it is placed in the activity series as it forms positively charged ions by losing electrons. In general it is found that:-
A metal higher up than hydrogen in the activity series can displace hydrogen from dilute acids or water. A metal lower down than hydrogen cannot displace it. Again a metal on the left hand side of hyudrogen will displace another metal on its right from the salt of the latter metal.

Question 3.
Write some uses of Graphite.
Answer:

1. As electrodes in batteries.
2. as the core of ‘bad’ pencils.
3. as a lubrcant in fast-moving machinery
4. in making heat resistant crucibles, that can with stand high temperatures and are used to melt small quantities of metals.

Question 4.
It is possible to keep CuSO₄ solution in an iron dish?
Answer:
No it is not possible to keep CuSO₄ solution in an iron dish as reactivity of iron is mere than copper. Iron will displace copper from CuSO₄ and form FeSO₄.
Fe + CuSO₄ → FeSO₄ + Cu.

Question 5.
Give some examples :
i) Two high electro-positive metal.
ii) Two low electro-positive metal.
iii) Two medium electro-positive metal.
Answer :
i) Two high electro-positive metals → Sodium, Potassium.
ii) Two low electro-positive metals → Copper, Silver.
iii) Two medium electro-positive metal → Zinc, Lead.

Question 6.
Discuss how certain elements help in formation of some important compounds in human body .
Answer:
Several compounds likephospholipid, nucleic acid, metalloprotein, amino acid etr.play vital roles in the formation of organelles, cell and tissues of the human body. The non-metals like C, H, O, N, P, S and metals like Fe, Cu Se, Mn are also involved in the formation of these compounds.

Question 7.
Discuss how certain elements jicrform maintenance of water balance, functioning of the heart, acid-base equilibrium in our body.
Answer:
Certain important functions are-
1. Maintenance of water balance in Human Body: Na⁺and K⁺are two principal cations of our intracellular and extracellular body fluids.
2. Functioning of the Heart: Concentration of Ca²⁺ and K^–controls the excitability and 1ythmic contraction expansion of the human heart.
3. Acid-Base Equilibrium: Acid-Base equilibrium is controled by K⁺. If the acid-base balance is lost, erosion of bone joints initiates (arthritis) and bone density gets lowered (osteoporosis).

Question 8.
Discuss how certain elements perform maintenance of formation of teeth and bone, functioning of enzymes, coagulation of Blood in our body.
Answer:
Certain important functions are-
i) Formation of teeth and bone: Calcium, Magnesium and Phosphorus are responsible for the mechanical strength of our teeth and bones.
ii) Functioning of Enzymes: Several metallic and non-metallic ions like Ca²⁺, Mg²⁺, Mn²⁺, Na⁺, Zn²⁺, Cl^–, Fe²⁺, Fe³+, Cu²⁺, PO₄^3- are use for the function of enzymes in the human body.
iii) Coagulation of Blood: Calcium ion (Ca²⁺) plays a very important function in activating different factors that participate in the process of coagulation.

Question 9.
Discuss how certain elements perform Constraction of muscle and conduction of nerve impulse, Transport, Storage and Utilization of Oxygen, formation of hormone in our body.
Answer:
Certain important functions are-
i) Constraction of muscle and conduction of nerve impulse : Ca²⁺, Mg²⁺, Na⁺and K⁺ control the excitability of muscles.
ii) Transport, Storage and Utilization of Oxygen: Haemoglobin in blood transports oxygen. Myoglobin in muscles stores oxygen. Iron is one of the indispensable components of these two proteins.
iii) Formation of Hormone: Zinc ion plays a significant role in the storage and stabilization of insulin hormone secreted from the pancreatic glands associated with the alimentary canal.

Question 10.
Name the metals and non-metals present in the compounds we use in our day to day life?
(i) Tooth paste
(ii) Gun powder of match stick
(iii) Chemical Fertiliser
(v) Stainless steel
(vi) Cement
(vii) Photographic film.
Answer:

i) Tooth paste	Carbon, Hydrogen, Oxygen, Aluminium, Calcium.
ii) Gunpowder of match stick	Red phosphorus, Chlorine. Oxygen, potassium.
iii) Plant and animal food	Carbon, Oxygen, Hydrogen. Nitrogen, S, P, Na, Ca, Mg, Fe, K
iv) Chemical Fertíliser	Nitrogen, Phosphorus, Potassium.
v) Stainless steel	Iron, Chromium, Carbon.
vi) Cement	Aluminium, Silicon, Oxygen.
vii) Photographic film	Silver, Carbon, Hydrogen, Oxygen.

Question 11.
Name the metals and non-metals present in the compounds we use in our day to day life?
Answer:

Metal	Non-metals
i. Metals are solids at room temperature, except mercury, which is liquid at room temperature.	i. Non-metals are gases or solids at room temperature, except bromine, which is liquid at room temperature.
ii. They are generally hard and strong, except sodium and potassium.	ii. Non-metal solids are generally not as hard as metals, however diamond is very hard.
iii. They have metallic lustre (shine).	iii. They do not have lustre, exception silicon and graphite have metallic lustre.
iv. They have high melting and boiling points exceptions are sodium, potassium, mercury and gallium.	iv. They have low melting and boiling points, exception graphite has high melting and boiling point
v. They are good conductors of heat and electricity.	v. They are bad conductors of heat and electricity, exception is graphite.
vi. They can be beaten into thin sheets and foils, exceptions are sodium and potassium.	vi. Non-meta!s can neither be beaten into thin sheets nor can be drawn into wires.
vii. Most metals have high tensile strength.	vii. They have low tensile strengths.
viii. They can be draw into wire, exceptions are sodium and potassium.	viii. They usually have low densities.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 8 Human Food and Food Production offer valuable context and analysis.

WBBSE Class 8 Science Chapter 8 Question Answer – Human Food and Food Production

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
The fowl that do not incubate eggs …………….
i) Brahma
ii) Cochin
iii) Leghorn
Answer:
iii) Leghorn.

Question 2.
Fish that is imported from foreign countries …………….
i) Rohu
ii) Grass Carp
iii) Mrigel
iv) Bata
Answer:
ii) Grass Carp

Question 3.
The fowls that produce eggs and meat …………….
i) Bahama
ii) Leghorn
iii) Aseel
iv) Rhode Island Red
Answer:
iv) Rhode Island Red

Question 4.
Mrigel and Common carp collect food in water from …………….
i) upper layer
ii) middle layer
iii) lower layer
Answer:
iii) lower layer

Question 5.
According to the location of fish production fisheries are of …………….
i) two types
ii) three types
iii) four types
iv) many types
Answer:
i) two types.

Question 6.
Example of major carp …………….
i) Rohu
ii) Bata
iii) Punti
iv) silver carp
Answer:
i) Rohu

Question 7.
Silver Carp is …………….
i) Major Carp
ii) Minor Carp
iii) Exotic Carp
Answer:
iii) Exotic Carp

Question 8.
A kharif crop …………….
i) gram
ii) groundnut
iii) mustard
Answer:
ii) groundnut

Question 9.
In their head fishes contain …………….
i) pituitary gland
ii) thyroid gland
iii) postrate gland
Answer:
i) pituitary gland.

Question 10.
a fibre crop …………….
i) tea
ii) paddy
iii) mango
iv) jute
Answer:
iv) Jute.

Question 11.
Green tea contains …………….
i) vitamin B complex
ii) vitamin C
iii) vitamin A
iv) vitamin K
Answer:
iv) vitamin K

Question 12.
A cereal crop is …………….
i) Tulshi
ii) Coffee
iii) Wheat
iv) paddy
Answer:
iii) Wheat

Question 13.
Which one is a decorative plant?
i) Tomato
ii) Potato
iii) banana
iv) Cactus
Answer:
iv) Cactus.

Question 14.
King of fruits …………….
i) mango
ii) banana
iii) grape
iv) orange
Answer:
i) mango

Question 15.
A Rabi Crop …………….
i) Paddy
ii) Barley
iii) Groundnut
iv) Cotton
Answer:
ii) Barley.

State whether True or False : (1 mark for each question)

1. Trailer is used for removing weeds and loosening the soil.
2. Small farmers use winnowing to separate grains from the chaff.
3. The food of the domestic animal is known as fodder.
4. Fresh crop has less moisture.
5. Infestation of the microbes can occur, if freshly harvested grains are stored without drying.
6. Presently oxygen gas is continuously circulated through the granaries.
7. Maize is an important crop of the world.
8. Paddy is one of the major food crop of India.
9. Aush paddy seeds are directly sowed in the agricultural field.
10. Swarna, Masuri paddy mature within 95-115 days.
Answer:
1) false
2) true
3) true
4) false
5) true
6) false
7) false
8) true
9) true
10) false

Fill in the blanks : (1 mark for each question)

1) Take branch of science in which the process of food production is discussed is ………….
2) When plants of the same kind are cultivated in a large area, the plants are collectively termed as ……….
3) The branch of agriculture in which the process of fruit and vegetable cultivation is discussed is called ………….
4) …………. and other microbes that live in the soil act as farmer’s friend.
5) ………… is used for removing weeds and loosening the soil.
6) ………… manure is produced by decomposition of dead plants and animal wastes.
7) …………. fertilisers are chemical substances.
8) The supply of necessary water to the crops in the field at definite intervals is termed as ………….
9) A big well and a wheel are used in …………. method.
10) The unnecessary plants that grow in the agricultural field are termed as ………….
11) The cultivation of …………. crop generally starts from the beginning of monsoon.
12) The cultivation …………. crops starts from the beginning of winter.
13) The …………. fly in hordes and cause severe damage to the crops like sugarcane, wheat by feeding on their leaves.
14) Fungi produce …………. disease in wheat and disease in potato.
15) Animals like rats can be controlled by…………. and ………….
16) …………. is an important job after the crop gains maturity.
17) Harvesting and threshing both can be done with the help of a machine called………….
18) The food of the domestic animals is known as ………….
19) ………….is one of the major food crop of India.
20) …………. paddy cultivation is more in West Bengal.
21) …………. is indigenous to India.
22) The original abode of tea is the basin of …………. river in South-east Asia.
23) We get…………. and …………. from honey-bee.
24) …………. honey bee collect nectar from flowers.
25) The culture of fishes arc called ………….
26) Birds which have economic importance at …………. called birds.
27) The female fish releases and the male fishes release the …………. when injected with pituitary extract.
28) Sperms and eggs unite to produce………….
29) Cotton is a…………. crop.
30) Black pepper is a ………….crop.
Answer:
1) agriculture
2) crop
3) horticulture
4) earthworms
5) hoe
6) organic
7) inorganic
8) irrigation
9) Rabat
10) weeds
11) Kharif
12) Rabi
13) locusts
14) rust, blight
15) Zinc phosphide, warfarin
16) harvesting
17) combine
18) fodder
19) Paddy
20) Anran
21) mango
22) Irawaddv
23) honey, wax
24) worker
25) pisciculture
26) poultry
27) eggs, sperms
28) spawns
29) fibre
30) spice.

Match the column A with column B

Column A	Column B
a) Tea is a	i) when organic manure is used
b) Hoc is used for removing weeds	ii) the roots of plants
c) Seed drill is a	iii) important commercially
d) Inorganic fertilisers are manufactured	iv) with queen honey bee
e) The soil becomes porous	v) and loosening the soil
f) Termites feed on	vi) plantation crop
g) High fluride content in tea leaves	vii) are reared for economic gain
ii) Male honeybee takes part in breeding	viii) in fertiliser factories
i) Minor carps are not	ix) prevents tooth decay
j) Birds like ducks and fowls	x) sowing tool

Answer:
a) Tea is a plantation crop.
b) Hoc is used for removing weeds and loosening the soil.
c) Seed drill is a sowing tool-.
d) Inorganic fertilisers are manufactured in fertiliser factories.
e) The soil becomes porous when organic manure is used.
f) Termites feed on the roots of plants.
g) High fluride content in tea leaves prevents tooth decay.
h) Male honeybee takes part in breeding with queen honeybee.
i) Minor carps are not important commercially.
j) Birds like ducks and fowls are reared for economic gain.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
Write names of two fibre crops :
Answer:
Cotton. Jute are two fibre crops.

Question 2.
Write names of two oil seeds.
Answer:
Mustard. Sunflower are two oil seeds.

Question 3.
Write names of two spice crops.
Answer:
Black pepper. Ginger are two spice crops.

Question 4.
What type of crops are Neem and Tulsi?
Answer:
These are medicinal crops.

Question 5.
Give example of two tuber crops?
Answer:
Potato and ginger are two tuber crops.

Question 6.
Name two crops from which we get sugar.
Answer:
Sugarcane and Beet are two crops from which we get suger.

Question 7.
What type of crops are Gram, Peas and Beans?
Answer:
Gram, Peas and Beans are pulses.

Question 8.
Give example of two Plantation crops.
Answer:
Tea and Coffee are two plantation crops.

Question 9.
What is horticulture?
Answer:
The process of fruit and vegetable cultivation is discussed in a branch Horticulture.

Question 10.
Write names of three vegetables.
Answer:
Tomato, Cabbage, Brinjal are three vegetables.

Question 11.
Name two decorative plants.
Answer:
Cactus, Bougainvillea are two decorative plants.

Question 12.
Give example of three Bower plants.
Answer:
Rose, Jasmine. Marigold are three flower plants.

Question 13.
When cultivation of Kharif crops start?
Answer:
The cultivation of Kharif crops start from the beginning of monsoon (June/July).

Question 14.
On which monsoon the production of Kharif crops depend?
Answer:
The production of Kharif crops depend upon the South-west monsoon.

Question 15.
Give some examples of Kharif crops?
Answer:
Some examples of Kharif crops are paddy, maize, cotton, groundnut, soyabean etc.

Question 16.
When cultivation of Rabi crops start?
Answer:
The cultivation of Rabi crops start from the beginning of winter (October/November).

Question 17.
When Rabi crop is harvested?
Answer:
The Rabi crop is harvested in the month of March/April.

Question 18.
Give some examples of Rabi crops?
Answer:
Some examples of Rabi crops are wheat, barby, gram, pea, mustard etc.

Question 19.
What is termed as Agricultural practices?
Answer:
The activities or tasks that a farmer does is termed as Agricultural practices.

Question 20.
What are a soil contains?
Answer:
The soil contains different minerals, water, air, humus and different organisms.

Question 21.
What is called friend of farmers?
Answer:
Earthworm is called friend of farmers.

Question 22.
What is ploughing?
Answer:
The process of turning and loosening the soil is called ploughing.

Question 23.
How is Hoe used?
Answer:
Hoe is used for removing weeds and loosening the soil.

Question 24.
What is used nowadays to plough large tracts land?
Answer:
Presently the help of tractor is taken to plough large tracts of agricultural land.

Question 25.
What is used nowadays to plough small agricultural land?
Answer:
For ploughing small agricultural land or flower garden nowadays power tiller is used.

Question 26.
How is seed drill used?
Answer:
Seeds can be sowed at the right distances and at requisite depths with the help of seed drill.

Question 27.
Why the farmers dip the seeds in chemicals before sowing?
Answer:
The farmers dip the seeds in chemicals before sowing as these chemical substances reduce the chances of infection of the seeds.

Question 28.
What are plant nutrients?
Answer:
Plants require some minerals for proper growth-these are termed as plant nutrients.

Question 29.
How many types of manure and fertilisers are there?
Answer:
They are of two types-organic manure and inorganic fertilisers.

Question 30.
How organic manure is produced?
Answer:
Organic manure is produced by decomposition of dead plants and animal wastes.

Question 31.
Cultivation of which crop increases nitrogen in soil?
Answer:
Cultivation of leguminous plants (pea, bean, gram, pulses) increases nitrogen in soil.

Question 32.
What is crop rotation?
Answer:
Cultivation of other crops like leguminous plants in between the cultivation of two similar type of crops is termed as crop rotation.

Question 33.
Write name of some common weeds.
Answer:
Some common weeds are-Parthenium, Amaranthus, Chenopodium, Grass etc.

Question 34.
What are two ways to control the pests?
Answer:
There are two ways to control the pests → chemical and biological.

Question 35.
What type of chemicals are used to control rats?
Answer:
Chemicals like zinc phosphide and warfarin are used to control rats.

Question 36.
Which chemicals control the insects?
Answer:
DDT, BHC. Malathion helps in controlling the insects.

Question 37.
Name some natural predators of some pests.
Answer:
Some types of spiders, wasps, hornets, grasshoppers and some kinds of birds are natural predators of some pests, like-moths, sapsucking insects, termites etc.

Question 38.
What is threshing?
Answer:
Edible part of the grain crops need to be separated from the plants, this is termed as threshing.

Question 39.
Presently which gas is used in granaries?
Answer:
Presently nitrogen gas is continuously circulated through the granaries, as a result the pests find it difficult to survive due to lack of oxygen.

Question 40.
Which is the major food crop of India?
Answer:
Paddy is one of the major food crop of India.

Question 41.
What is the nutritive value of rice?
Answer:
Rice contains 79 1% carbohydrate, 6% protein, 011% different elements, Vitamin B complex and some other vitamins.

Question 42.
What is produced from rice bran?
Answer:
Oil is produced from rice bran.

Question 43.
What are the types of paddy based on the generic variety and method of cultivation?
Answer:
These are Aush or Autumn paddy, Aman or Winter paddy and Boro or Summer paddy.

Question 44.
What are the types of paddy based on the production capacity?
Answer:
Based on the production capacity paddy are of two types.

Question 45.
When Aman paddy is cultivated?
Answer:
Aman paddy is cultivated during the Monsoon season.

Question 46.
Name some good varieties of indigenous Aman paddy.
Answer:
Good varieties of indigenous Aman paddy-Bhashamanik, Jhingasal, Raghusal, Patnai- 23. Basmati etc.

Question 47.
When Boro is harvested?
Answer:
Boro is harvested in March-April.

Question 48.
How much time Ratna Paddy takes to nature?
Answer:
Ratna Paddy mature within 95-115 days.

Question 49.
How much time .lava, Jayanti Paddy takes to mature?
Answer:
Jaya, Jayanti Paddy mature within 116-135 days.

Question 50.
Name some varieties of Nabi or Long duration variety Paddy.
Answer:
Some varieties of Nabi or Long duration variety Paddy are Swarna. Masuri, Pankaj etc.

Question 51.
What is golden rice?
Ans.
Golden rice is a special types of Paddy created by agricultural scientists to meet the demand of Vitamin A.

Question 52.
What is the birth place of Mango?
Answer:
India is the birth place of Mango.

Question 53.
In which places Mango is cultivated in West Bengal?
Answer:
In West Bengal Mango is cultivated mostly in Makla, Murshidabad and Nadia.

Question 54.
What type of soil is suitable for Mango cultivation?
Answer:
Alluvial soil of river basin and fertile loamy soil is the most suitable for Mango cultivation.

Question 55.
What are the different ways of grafting done in Mango?
Answer:
Grafting done in Mango in various way-lnarching. Veneer grafting. Chip budding. Stone grafting.

Question 56.
Name Some varieties of Mango.
Answer:
Some varieties of Mango are Himsagar, Bombai, Langra, Golapkhas, Chausa etc.

Question 57.
What are the World’s largest tea producing countries?
Answer:
World’s largest tea producing countries are China. India. Kenya, Srilanka and Turkey.

Question 58.
Name the main tea producing states of India.
Answer:
The main tea producing states of India are Assam. West Bengal. Tamilnadu and Kerala.

Question 59.
What are the famous tea of India?
Answer:
The famous tea of India is Darjeeling. Assam and Nilgiri.

Question 60.
How are tea plants propagated?
Answer:
Tea plants are propagated both from seeds and plant parts.

Question 61.
How many types of commercial tea are there based on the method of manufacture?
Answer:
They are of three types- Black tea. Green tea and Oolong tea.

Question 62.
What we get from honey bees?
Answer:
We get honey and wax from honey bees.

Question 63.
Name the types of honey bees present in honey bee society.
Answer:
They are queen honey bee, male honey bee and worker honey bee.

Question 64.
What is the nutritional value of honey?
Answer:
honey contains lots of glucose and fructose, amino acids, other minerals (Na, K, Ca, Fe, Mg, P), vitamin A, B-complex and C.

Question 65.
What are the four stages of life of honey bee?
Answer:
Four stages of life of honey bee are-egg, larva, pupa and adult.

Question 66.
What is apiculture?
Answer:
Rearing of honey Bees in a scientific and artificial way is termed as apiculture.

Question 67.
What is apiary?
Answer:
Rearing place for the honey bees, be it natural or artificial is termed as apiary.

Question 68.
What the culture fishes are called?
Answer:
The culture fishes are called Pisciculture.

Question 69.
What is fertilisation.
Answer:
The process of unification of eggs with the sperms is called fertilisation.

Question 70.
Name the ponds the spawns are reared one after another.
Answer:
These ponds are termed as nursery pond, rearing pond and stocking pond.

Question 71.
What is composite fish culture?
Answer:
Culture of three types of indigenous fishes in one single pond is termed as Composite Fish culture.

Question 72.
What is Composite Mixed Fish Culture or Polyculture?
Answer:
Culture of three types of indigenous carps with three types of exotic carps in one single pond is termed as Composite Mixed Fish culture or Polyculture.

Question 73.
What is the primary food of fishes?
Answer:
The primary food of fishes are phytoplanktons.

Question 74.
What is sewage?
Answer:
Generally water of black colour mixed with waste materials from houses, municipalities and factories is termed as sewage.

Question 75.
What is sewage used for?
Answer:
Sewage is used for fish culture in the Vheris in East Kolkata.

Question 76.
What is nutritional value of fish?
Answer:
Fishes supply animal protein, essential amino acids, fatty acids, various minerals (eg. Ca, P, Na, K. Mg. S) and some vitamins (A, C. D and B-Comple.).

Question 77.
What is Broiler?
Answer:
Broiler is a type of hybrid fowl bird created for only getting meat.

Short Questions & Answers : (2 marks for each question)

Question 1.
What arc the types of paddy, based on the time needed for maturity?
Answer:
They are-

• Jaldi or Early duration varieties
• Majhari or Medium duration varieties
• Nabi or Long duration varieties.

Question 2.
Why are manure and fertilisers added to soil?
Answer:
The plant nutrients present in the soil are depleted when the same land is used for repetative cropping. For this reason, manure and fertilisers are added to the agricultural land. This ensures that the soil gets back the lost nutrients.

Question 3.
What requirements are l’ulfdled by Inorganic fertilisers?
Answer:
Inorganic fertilisers mainly meet the requirement of three types of elements – nitrogen (N), phosphorus (P) and potassium (K).

Question 4.
What harm occurs if ammonium sulphate and sodium nitrite is not used in accordance with the properties of the soil?
Answer:
Ammonium sulphate [(NH₄)₂SO₄] increases the acidity of the soil and Sodium nitrite (NaNO₂) increase the alkalinity of the soil.

Question 5.
What is irrigation?
Answer:
Maintenance of soil humidity is essential for getting a good production. For this reason, it is necessary’ to supply water to the crops in the field at definite intervals. This is termed as irrigation.

Question 6.
What are weedicides?
Answer:
Weeds are also controlled by spraying some chemicals (2, 4-D, Dalapon. Picloram etc). These chemical substances are called weedicides.

Question 7.
How many plant nutrients are there? What are they?
Answer:
The plant nutrients are of two types :

• Macronutrients – C, H, O, N, P, K, Mg, S
• Micronutrients – Ce, Mil, Cu, B. Mo. Zn, Cl.

Question 8.
What is grafting?
Answer:
Grafting is a kind of propagation in plant made in the artificial way. In grafting a new plant is produced from a part of the plant.

Question 9.
What is fodder?
Answer:
Parts of the stem that remain in the ground after the crop is harvested and the chaff are fed to the domestic animals. This food of the domsestic animals is known as fodder.

Question 10.
What is the nutritional value of Mango?
Answer:
Mango contains protein, fat and minerals (Ca. P. Fc) etc. It also contains Vitamin A, B- Complex and C, water, fibres and phyto chemicals (Beta-Carotene).

Question 11.
What is hot chery?
Answer:
The fertilised eggs collected by the fish farmers are reared in a pond to produce spawns. This pond is termed as the hot chery.

Question 12.
What is animal husbandry?
Answer:
To get animal-based food products regularly and sufficient quantities, those animals need to be reared with care and along with arrange for their breeding, this is animal Husbandly’.

Question 13.
What are pests? Name some of them.
Answer:
Rats, various insects feed on the crops or damage the crops, they are termed as pests. Some pests are-locust, termite, weevil, stem borer etc.

Question 14.
What is NPK?
Answer:
NPK is inorganic fertiliser which has thee components-nitrogen (N), phosphorus (P) and potasium (K) mixed in differant proportions. This help in the growth of plant.

Long Questions & Answers : (3 marks for each question)

Question 1.
Describe the topics that arc relevant to Agriculture.
Answer:

• Soil management, i.e to make soil suitable for production of crops.
• Crop production
• Horticulture, i.e cultivation of fruits, vegetables, flowers and decorative plants.
• Animal Husbandry.

Question 2.
List the activities that a farmer has to perform to produce crops.
Answer:

• Preparation of soil of cultivable land
• Sowing of seeds
• Adding manure and fertilisers
• Irrigation
• Protection from weeds
• Protection from pests
• Harvesting
• Storage

Question 3.
What is a plough?
Answer:
Plough has been used in cultivation for a long time. Plough is used for ploughing the field, mixing fertilisers with the soil or removing weeds. Presently indigenous wooden ploughs are gradually being replaced by ploughs made of iron.

Question 4.
Briefly describe how the farmers sow seeds? also explain why?
Answer:
Sometimes the farmers dip the seeds in chemicals before sowing. These chemical substances reduce the chances of infection of the seeds. Seeds of paddy and some vegetables (tomato, onion) are sowed first in seed-beds.

After the seedlings have grown a bit in the seed-bed, healthy, strong and disease-free seedlings are selected and planted in the agricultural field. Seedlings of improved quality can thus be selected. The transplanted seedlings are also able to penetrate their roots deep in the soil. As a result the production also increases.

Question 5.
What are the problems in using inorganic fertilisers?
Answer:

• Excessive and indiscriminate use of inorganic fertilisers create problems in the functioning of soil-living beneficial bacteria. Thus, the soil fertility is reduced.
• Inorganic fertilisers sometimes change the soil chemestry. Like ammonium sulphate ((NH₂SO₄) increases the acidity of the soil whereas sodium nitrite (NaNO₂) can increase the alkalinity of the soil.
• River or pond water near agricultural field becomes polluted by coming or contact with nitrogen or phosphorus compound present in inorganic fertilisers.

Question 6.
Why organic manure is better than inorganic fertilisers?
Answer:

• Organic manure increases the water retention capacity of the soil.
• The soil becomes porous when organic manure used.
• Organic manure helps to increase the number of beneficial microbes present in the soil.
• Organic manure improves soil texture.

Question 7.
What are biofertilisers?
Answer:
Sometimes various microbes are mixed with the soil to maintain the nutrients present in the soil. This is termed as biofertilizers. Biofertilisers increase the water retaining capacity of the soil. They make the soil porous and increase aeration in the soil.

Question 8.
Why is irrgation essential for plants?
Answer:
Irrigation is essential because-

• Water is needed for the growth of plants and development of flowers fruits and seeds.
• Plants take various nutrients and fertilisers from the soil through water.
• The nutrients reach different plant organs mixed with the water.
• Water is very essential for the germination of seeds.
• Maintenance of soil humidity is essential for getting a good production.

Question 9.
How irrgation is done in fields?
Answer:
Two methods of irrigation is done in fields-
i) Traditional methods : Human or animal labour is generally used in the traditional methods of irrigation.- Some such methods are-

• Rope-bucket-pulley-moat method,
• Swing basket method
• Chain pump method
• Dhekli method
• Persian wheel or Rabat method.

ii) Modern method : Traditional methods are cheaper, but are less effective and misuse of water happens. Misuse of water can be reduced by modern methods. Some such methods areal Sprinkler

• system: water is sprinkled on the crops like a fountain.
• Drip system: water is supplied near the foots of the plants in drop by drop manner with the help of a pipe.

Question 10.
What are the problem of controlling pests with chemicals like DDT, BHC etc?
Answer:

• The pests can develop resistance against a specific chemical.
• The chemicals may cause water pollution by mingling with the water of rivers or lakes.
• Organisms at the end of the food chain can be harmed if these chemicals enter the food chain.
• These chemicals can harm human beings if they enter the human body through fruits and vegetables.
• The chemicals sometimes kill beneficial insects (honeybees, butterflies)

Question 11.
How biological control method is used to control pests?
Answer:
In biological control method an organism is used in controlling the number of another organism in this method. The help of predators and parasites are taken to control the pests. Some types of spiders, wasps, hornets, grasshoppers and some kind of birds are nature predators of some pests (like moths, sap-sucking insects, termites etc) Some fungi, protozoa bacteria and viruses live as parasites inside the body of the pests and control the pest population.

Question 12.
Describe briefly how Inarching is done in mango.
Answer:
Inarching grafting is done by joining a branch of a high quality mango tree (scion) with a seedling (stock) produced from mango seed. Generally this grafting is done in July-August (Bengali month Ashar).

• Some part is cut from both the seedling and the branch of the high quality mango tree. Then they are joined in the cut portion with a string. The seedling is watered regularly till the joining is complete,
• After the joining is complete, the lower portion of the scion below the joined part and upper portion of the seedling above the joined part is cut of in 2 or 3 phases.
• The plant produced by inarching is kept in the shades for some days. Then it is transplanted in the nursery.

Question 13.
Write four nutritional value of tea.
Answer:

• Drinking tea stimulates the body due to the presence of caffeine
• Tea cantains Havonoids, tannis. volatile oils and vitamin B. which are good for health.
• High fluoride content in tea leaves prevents tooth decay.
• Black tea contains high amounts of vitamin B-complex and folic acid which are anti-ulcer and anti-carcinogenic in nature.

Question 14.
Describe the different types of work done by the different types of honeybees.
Answer:
Each of the three types of honeybee has specific job-

• queen honeybee lays egg.
• Male honeybee takes part in breeding with queen honeybee,
• Worker honeybee has many jobs to do-constructing beehive, collecting pollen grains and nectar, taking care of queen and male honeybees, producing honey and wax, rearing the young ones, guarding the beehive.

Question 15.
How do the honeybees construct the beehive and produce honey?
Answer:
Worker honeybee has a wax gland in their abdomen. They construct the beehive with the secretion of the wax gland. Numerous hexagonal chambers are present in each beehive. Worker honeybees collect necter from flowers. They store the nectar in the honey sac of their own body.

In the honeysac, saliva mixes with nectar. As a result, some changes occur in the carbohydrates present in nectar. Warker honeybee vomits this mixture in the honey chamber and fan it with their wings. As a result water is vapourised, thus producing honey.

Question 16.
What are carps? How many types of carps are there?
Answer:
Carps are those bony fishes living in fresh water characterised by the absence of scales on triangular head, accessory respiratory organ, tooth in the jaw and the presence of swim bladder in their body. For example, Rohu, Catla, Bata etc. Carps can be divided in two types :
i) Indigenous carp →

• Major Carp
• Minor Carp.

ii) Exotic carp.

Question 17.
Differentiate between Major earp and Minor carp.
Answer:

Major carp	Minor carp
i) Big in size. ii) Grows quickly. Generally do not spawn in enclosed water. iii) They are commercially important and their demand is also more. Example : Rohu, Catta	i) Small in size. ii) Do not grows quickly. Generally spawn in enclosed water. iii)They are not important commercially. Example : Bata, Punti etc.

 

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.1 Force and Pressure offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.1 Question Answer – Force and Pressure

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
A push or pull on an object is called as–
i) push-pull
ii) force
iii) pressure
iv) all of above
Answer:
ii) force

Question 2.
What is the cause of change in motion or change in the state of motion?-
i) pressure
ii) friction
iii) atmospheric pressure
iv) force
Answer:
iv) force

Question 3.
A ball rolling on the ground slows down and finally stops. It is because of –
i) force
ii) less force
iii) friction
iv) none of the above
Answer:
iii) friction

Question 4.
Pressure is defined as-
i) Area/Force on which it acts
ii) Force/Area on which it acts
iii) Volume/Force on which it acts
iv) Force/Volume on which it acts
Answer:
ii) Force/Area on which it acts

Question 5.
In a tag of war, two teams pulling a rope does not move towards any team, it implies that-
i) An equal force is being applied in the opposite direction
ii) An equal force is being applied in the same direction
iii) No force is applied in any direction
iv) Can not be explained
Answer:
i) An equal force is being applied in the opposite direction

Question 6.
When two forces, applied on an object, are equal and opposite, then the forces-
i) May move the object
ii) May stop a moving object
iii) May move the object and also cause a change
iv) Do not move the object but may cause a change in its shape
i Answer:
iv) Do not move the object but may cause a change in its shape

Question 7.
Friction produces-
i) light
ii) alpha rays
iii) heat
iv) all of the above
Answer:
iii) heat

Question 8.
A liquid exerts pressure in directions-
i) upward
ii) downward
iii) sidewards
iv) all
Answer:
iv) all

Question 9.
The air prèssure on our body is equal to-
i) Atmospheric pressure
ii) sea botton pressure
iii) space pressure
Answer:
i) Atmospheric pressure

Question 10.
The SI unit of pressure is-
i) N m³
ii) N m²
iii) kg m²
iv) pa m²
Answer:
ii) N m²

Question 11.
The standard atmospheric pressure is –
i) pressure of a mercury column of height 76 cm
ii) mercury of 10 metre
iii) pressure of 76 mm mercury column
is Answer:
i) pressure of a mercury columin of height 76 cm

Question 12.
The upward force exerted on a body by the fluid in which it is submerged is called the –
i) Immersion
ii) Buoyancy
iii) Weight
Answer:
ii) Buoyancy

Question 13.
On which of the following pressure of liquid does not depend –
i) depth of liquid
ii) upper surface area of liquid
iii) density of liquid
Answer:
ii) upper surface area of liquid

Question 14.
Density of saline water is – than purified water.
i) more
ii) less
iii) same
Answer:
i) more

Question 15.
Density of mercury is –
i) low high
iii) very high
iv) very low
Answer:
iii) very high

State whether True or False : (1 mark for each question)

1. Presure of saline water is greater than purificd water.
2. Buoyancy is a kind of force.
3. If the weight of an object is greater than buoyancy of that object it gets immerged in water.
4. Pressure on any point of liquid is same.
5. In SI system unit of pressure is Newton/meter ²
6. Density of kersone oil is less than desnity of water.
7. Buoyancy acts towards the weight of an object.
8. The syringe works on a principle of atmospheric prussure.
9. Newton’s first law of motion is alternatively called as law of inertia,
10. Cutting and piercing tools have blunt edeges.
11. Camel can not walk on sand due to its broad feet.
12. Force of friction is greater in case of smeoth surface.
13. Fluids exert pressure.
14. When an object remains stationary on a surface, the object exerts downward force on the surface vertically
15. Pressure and force dscides the direction of flow of a liquid.
Answer:
1. true
2. false
3. true
4. false
5. true
6. true
7. false
8. true
9. true
10. false
11. false
12. false
13. true
14. true
15. fale

Fill in the blanks : (1 mark for each question)

1. Force = mass of the objeet × ______.
2. SI unit of measuring forte ______.
3. When you are holling a weight of 1 kg in your hand, the force that is applied on your hand is around ______ Newton.
4. We can change the derection of a moving body by applying ______.
5. Litre is the unit of ______.
6. Frictional force works against the ______ of an object.
7. In SI system unit of density is ______.
8. Density of nercury = ______ gram/cubic centimetre.
9) Mass = Density × ______.
10. The force per unit area applied to the surface of a object is known as ______.
1Question 1. The strength of force is usually expressed by its ______.
12. Powder is sprinkled on the carom board to reduce ______.
13. Sliding friction is ______ than the static friction.
14. Friction depends upon ______ of the surface.
15. Water and other liquid exerts ______ when objects move through them.
Answer:
1. acceleration
2. Netwon
3. 9.8
4. force
5. volume
6. velocity
7. Kg m³
8. 13.6
9. volume
10. pressure
11. magnitude
12. friction
13. smaller
14. nature
15. force of friction.

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) In CGS system unit of force is	i) Buoyancy
b) If density incrase presure of liquid	ii) is greater than purified water.
c) Value of acceleration due to gravity	iii) 980 cm / sec2
d) The principle of buoyancy is stated by	iv) measuring cylinder
e) Upward force exerted on a body is called	v) is called acceleration
f) Density of saline water	vi) 980 cm / sec2
g) Volume of liquid is measured by	vii) dyne
h) The rate of change of velocity with time	viii) scientist Archimedes
i) Density of water is	ix) increase

Answer:
a) In CGS system, unit of force is dyne.
b) If density increase pressure of liquied increase.
c) Value of acceleration due to the gravity 980 cm sec²
d) The principle of buoyancy is stated by scientist Archimedes.
e) Upward force exerted on a body is called buoyancy.
f) Density of saline water is greater than purified water.
g) Volume of liquid is measured by measuring cylinder,
h) The rate of change of velocity with time is called acceleration.
i) Density of water is lg cm³.

b) Match the column A with column B.

Column A	Column B
a) A liquid exerts pressure	i) law of inertia
b) Pressure decides the direction	ii) is the unit of area
c) Density of the substance	iii) to reduce friction
d) Newton’s first law of motion	iv) is less than water
e) Lubricant is used	v) of a liquid
f) Fluids	vi) exert pressure
g) Square meter	vii) in all directions
h) Density of kerosene oil	viii) mass of unit volume of any substamce

Answer:
a) A liquid exerts pressure in all directions.
b) Pressure decides the direction of a liquid.
c) Density of the substance mass of unit volume of any substamce.
d) Newton’s first law of motion law of inertia.
e) Lubricant is used to reduce friction.
f) Fluids exert pressure .
g) Square meter is the unit of area.
h) Density of kerosene oil is less than water.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What is the SI unit of force?
Answer:
Newton.

Question 2.
What is the unit of pressure?
Answer:
Pascal.

Question 3.
What is the rate of change of velocity called?
Answer:
Acceleration

Question 4.
What is unit of acceleration is CGS system?
Answer:
cm sec²

Question 5.
What is the CGS unit of pressure?
Answer:
dyne / cm².

Question 6.
What is density?
Answer:
Mass of unit volume of any substance is known as density of the substance.

Question 7.
What is the SI unit of density?
Answer:
kg m³

Question 8.
Gallon is the unit of which substance?
Answer:
A gallon is a unit of measurement of density of liquids.

Question 9.
What is pressure?
Answer:
The force per unit area applied on the surface of an object is known as pressure.

Question 10.
If same force is exerted on a substance and area increases then will the pressure increase or decrease?
Answer:
pressure will decrease.

Question 11.
Name the instrument which is used to measure liquid pressure?
Answer:
Monometer.

Question 12.
Is friction is same for sll the surfaces?
Answer:
No.

Question 13.
What is the weight of substance?
Answer:
The weight of a body is the force with which the earth attracts it.

Question 14.
Due to which acceleration a substance fall downwards?
Answer:
Acceleration due to gravity.

Question 15.
What is the SI unit of acceleration due to gravity?
Answer:
9.81 in 7 sec².

Question 16.
Force of friction is greater in case of rough surface or smooth surface?
Answer:
Rough surface.

Question 17.
Give an example to show friction produces heat.
Answer:
Rubbing of our palm produces heat.

Question 18.
Can we reduce friction to zero by using lubricants?
Answer:
No it is not possible to entirely eliminate friction.

Question 19.
Name the device used for neasuring force acting on an object.
Answer:
Spring balance.

Question 20.
Does acceleration due to gravity depend on mass?
Answer:
No.

Question 21.
When upthrust would be greater saline water or pure water?
Answer:
Saline water.

Question 22.
From, which Newton’s law we get a concept about action and recation?
Answer:
Newton’s thisd law of motion.

Question 23.
What ts the realtion between force, mass and accleration acting on an object?
Answer:
Force = mass of the object × acceleration.

Question 24.
What is the density of water in SI sytem?
Answer:
1000 kg cc.

Question 25.
Whose unit is square meter?
Answer:
Square meter is the unit of area.

Question 26.
What is acceleration?
Answer:
Acceleration is the rate of change of velocity with time.

Question 27.
What is SI unit of acceleration?
Answer:
SI unit of acceleration is m sec².

Question 28.
Why vehicles slow down when breaks are applied?
Answer:
Because of friction.

Question 29.
What is spring balance?
Answer:
Spring balance is a weighing device which is used to measuring on an object.

Question 30.
What happens when the forces ars applied on an object in the same direction?
Answer:
Forces applied on an object in the same direction add to one another.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is force?
Answer:
A force is that physical cause which change (or tends to change) either size or shape or the state of rest or motion of the body.

Question 2.
Define friction?
Answer:
Friction is a force that resists the motion of an object that is in contact with another object or material.

Question 3.
What is frictional force?
Answer:
A force is that pliysical cause which clianges (or tends to change) eitrher size or shape or the state of rest or motion of the body, along the surface in contact. This is called the frictional force or the force or the force of frictions

Question 4.
Define static friction.
Answer:
Static friction is the friction between two or more solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a slopped surface:

Question 5.
Define sliding friction.
Answer:
When the object starts to move on being pulled, the frictional force which operates is known as sliding friction.

Question 6.
Write the formula of pressure per unit area in liquid.
Answer:
Pressure = depth × density of liquid × acceleration due to gravity.
∴ Pressure (p) = h d g
Where h = depth, d = density, g = gravity.

Question 7.
Same volume of water is taken in a tumbler and in a pipe-shaped vessel, which will exert more pressure?
Answer:
Pipe-shaped vessel will exert more pressure, because = depth × density of .liquid × acceicration due to gravity. Depth of pipe-shaped vessel is greater-than tumbler so it exerts more pressure than tumbler.

Question 8.
Why kerosene oil floats on water?
Answer:
Density of kersosene oil is less than water so kerosene oil floats on water. That means, mass of 1 cc of kerosene is less than same amount of water. So kerosene oil floats on water.

Question 9.
What is acceleration to gravity?
Answer:
When a body falls freely under gravity, the acceleration produced in the body due to the earth’s gravitational attraction is called the acceleration due to gravity.

Question 10.
State Pascal’s law of fluid.
Answer:
Pascal’s law states that if pressure is applied at any point on an enclosed liquid, it is transmitted equally in all direction, with undiminished force, and acts right angles to the surface of the vessel.

Question 11.
Can Pascal’s law be applied on water of a pond?
Answer:
No, Pascal’s law is not applicable on water of a pond as it not enclosed. Pascal’s law is applicable on enclosed liquid.

Question 12.
What is stądard atmosphric pressure.
Answer:
At 45° latitude the pressure exerted by a vertical column of height 76 cm is called standard atmospheric pressure.

Question 13.
With what gravitational force earth pulls towards its gravity, a 7 kg mass object?
Answer:
Gravitational pull of 7 kg mass object = 7 × 9.8 newton = 68.6 newton.

Question 14.
Will the height of mercury column be 76 cm everywhere on earth-explain.
Answer:
Atmosphheric pressure is not the same at all places. Its value is maximum at sea level and decreases as we go to higher altitudes. So the height of mercury column will not be 76 cm every where on earth.

Question 15.
Give two examples of the property of equilibrium.
Answer:
Two examples are-
i) Artesian well ii) water suppling system of city.

Question 16.
Define Buoyancy.
Answer:
When an object is immersed in a liquid, then the liquid exerts an upward force on the object. This force is known as buoyancy.

Question 17.
Give some example to support the statement that ‘friction is important for most of our day to day activities’.
Answer:
For writing with a pen or pencil, for fixing nail in the wall, for lightening of a match stick etc friction is used.

Question 18.
Why sole of shoes are grooved?
Answer:
Sole of shoes are grooved to increase friction so as to provide shoes a better grip on the floor.

Question 19.
Mention Newton’s first law of motion.
Answer:
A body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.’

Question 20.
‘Mention Newton’s second law of motion.
Answer:
The greater force applied on an object, the greater is the acceleration or change of velocity of the object per second.

Question 20.
Mention Newton’s third law of motion.
Answer:
When an object exerts a force on another object, the latter also exerts an equal and opposite force on the former.

Long Questions & Answers : (3 marks for each question)

Question 1.
Describe Archimede’s principle.
Answer:
Archimede’s principle states that if a body is partly or wholly immersed in a liquid it experiences an apparent loss in weight due to upthrust and the apparent loss is equal to the weight of the liquid displaced by the immersed part of the body.

Question 2.
How will you proof that when an object is immersed in water the object had an apparent loss of weight?
Answer:
A heavy object is hung from a spring balance. The weight of the object can be found from the recording of the spring balance. Now the object is immersed in a liquid while it hung from the spring balance. We will observe that the recording of the spring balance is lowered due to immersion of the object into the liquid. This occurs as the liquid exerts an upward force on the object.

Question 3.
What are factors that affect the upthrust?
Answer:
The upthrust due to a liquid on a body depends on the following two factors :
i) the volume of the body submerged in the liquid, and
ii) the density of the liquid, in which the body is submerged.

Question 4.
Why the walls of dams at the base are made thicker?
Answer:
We know that a liquid exerts the same pressure in all directions at a given depth. Pressure exerted by a liquid = height of liquid column × density of the liquid × acceleration due to gravity. So lateral pressure increases with the depth of liquid. On the upper portion of the dam density is less so the pressure is also less. Walls of dams at the base are made thicker in order to withstand the grater lateral pressure of water at that depth.

Question 5.
Why a piece of the thermocol flaots on water while an iron nail sinks in water?
Answer:
The piece of thermocol floats, while the iron nail sinks. The difference in behaviour of the two obviously lies in the difference in their densities. The density of thermocol is less than the

Question 6.
Define the teums thrust and pressure. What is the relation between them?
Answer:
The force acting normally on a surface is called the thrust. The thrust on unit area of the surface is called the pressure. The relation between thrust and pressure is Thrust = Pressure × Area.

Question 7.
Why ice floats on water?
Answer:
The density of ice is less than the density of water. The density of ice is 0.917³ gm and that of water is 1 g cm³ .12 cc ice melts and we get 11 cc water. When ice is submerged in water it displaces water lesser than density of water. So ice floats on water.

Question 8.
Why a piece of iron unimerges in water but floats on mercury?
Answer:
Density of iron is greater than water. So the weight of iron is greater than the buoyant force of water so iron sinks is water. Mercury has greater density than iron. So when iron is immersed in mercury weight of iron is less than the buoyant force of mercury so it floats on mercury.

Question 9.
It is easier for a man to swim in sea water than in fresh (or river) water, why?
Answer:
The reason is that due to the presence of minerals (salt etc), the density of sea water ( = 1.026 g cm³) is more than the density of fresh (or river) water ( = 1.0 g cm³). When a small portion of the body of a mark submarges in sea water, the weight of sea water displaced becomes equal to the total weight of the body. While to displace the same weight of freșh (or river)-water, a large portion of the body will have to be submerged in water. So it becomes difficult to swim in river water.

Question 10.
An iron nail sinks in while a ship-floats, why?
Answer:
If we place an iron nail on the surface of water, it sinks. This is because the density of iron is greater than of water, so the weight of the nail is more than the upthrust of water on it (or the weight of water displaced by the nail). On the other hand, ships are also made of iron, but they do not sink because the ship is hollow and the empty space in it contains_air which makes the average density of ship less than that of water. Therefore the weight of watêr displaced by the submerged part of the ship becomes equal to the total wieght of the ship and therefore the ship floats.

Question 11.
Why deep sea divers need special protective suit?
Answer:
The sea divers need special protective suit to wear because in a deep sea, the total pressure exerted on the diver’s body becomes much more than his blood pressure. To withstand it, he needs to wear a special protective suit. otherwise his body would get crushed.

Question 12.
Why there is possibility of sinking of a ship when it sails from sea water to river water?
Answer:
The density of sea water is more than the density of river water. According to the law of floatation, to balance the wieght of ship, a greater volume of water is required to be displaced. Therefore, when a ship sails from the sea of water of higher density to the river of water of lower density, possibility arises of sinking of ship.

Question 13.
Explian the property of equlilibrium of liquid.
Answer:
If water is poured in different vessels and if they are connected with each other, it will be each other, it will be observed that the level of water in each vessel will be same. This property of liquid seeking its own level is called the property of equilibrium.

Question 14.
What is Torricellian vaccum? What is there in this vacuum?
Answer:
Al m long tube is filled completely with pure and clear mercury and inverted into a through containing mercury. Some mercury from the tube flows down into the through. The mercury column now stands at a height of 76 cm above the surface of the mercury surface in the through, creating an empty space, near the closed end of the tube, this is called Torricellian vacuum. Mercury vapour fills this Torricellian vaccum.

Question 15.
What are the different types of friction?
Answer:
Friction are of two types-(i) Static Friction and (ii) Sliding friction.
i) Static Friction : When a object remains static on a surface, even through it has been pulled with a force, then the frictional force which operates is known as Static Friction.
ii) Sliding Friction : When the object starts to move on being pulled, the frictional force which operates is known as Sliding Friction.

Mathematical Problems ; (3 marks for each question)

Question 1.
Mass of an object is 5 gram and pressure of 10 dyne is exerted upon it. What amount of acclaration will be created?
Answer:
Force = mass of the object × acceleration
Acceleration = \(\frac{mass} {force} = \frac{10}{5}\) cm sec² = 2 cm sec².

Question 2.
Mass of an object is 2 kg. What would be its weight?
Answer:
Weight = Mass × Acceleration due to gravity
Acceleration due to gravity = 9.8 m sec²
∴ Weight = 2 × 9.8 newton = 19.6 newton.

Question 3.
Find out the amount of pressure at the base of a 10 m deep clear water lake. Atmospher’e pressre = 76 cm presure of mercury column and density of mercury = 13.6 gm cm³
Answer:
Pressure of base of lake = Atmospheric pressure + pressure of 10 m death water. = 76 × 13.6 × 980 + 10 × 100 × 1 × 980
= 980(76 × 13.6+10000) dyne cm²
= 980 × 2033.6 dyne cm² = 1.993 × 10⁶ dyne cm²

Question 4.
If density of mercury is 13.6 gm cm³, then find the mass of 1 lit mercury?
Answer:
Density of mercury is 13.6 gm cm³
∴ Mass of 1 cm³ mercury = 13.6 gm
Now I lit = 1000 cm³
∴ Mass of 1000 cm³ or 1 lit mercury is
1000 × 13.6 gm = 13600 gm = 13.6 kg

Question 5.
Find out the pressure of 10 cm deep water column.
Answer:
pressure of water column (p) = h d g
when h = depth = 10 cm
d = density of water = 1 g cm
g = 980 cm sec²
∴ p = 10 × 2 × 980 dyne = 9800 dyne cm²

Question 6.
Find the value of standard and atmospheric pressure or 76 cm. mercury column in SI unit.
Answer:
We know that pressure (p) = h d g here h = 76 cm
d = density of mercury = 13.6 g cm
g = acceleration due to gravity = 980 cm sec²
∴ p = 76 × 13.6 × 980 dyne cm² = 1012928 dyne cm²
Newton / m² = 10129280 Newton / m² = 1.012928 × 10⁷ pascal.

Question 7.
If water is kept instead of mercury in barometer then find out the height of water.
Answer:
Of mercury barometer, height h₁ and density d₁
then p = h₁ d₁ g (g = acceleration due to gravity)
Again of water baremeter height is h₂ and density is d₂
then p = H₂ d₂ g
∴ h₁ d₁ g = h₂ d₂ g
Now height of mercury barometer is (h₁) = 76 cm
density of mercury = 13.6 g/cc
again density of water = 1 g/cc
76 × 13.6 × g = h₂ × 1 × g
∴ h₂ = 76 × 13.6 = 1033.6 cm = 10.34 m

Question 8.
A square plate of side 10 m is place horizontally 1 m bleow the surface of water. The atmospheric pressure 1.013 × 10⁵ N m². Calculate the total thrust on the plate.
(Density of water d = 10³ kg m³ g = 9.8 m s² )
Answer:
Pressure due to 1 m cloumn of water = 1 dg
= 1 × 10³ × 9.8 = 0.098 × 10⁵ N m²
∴ Total pressure at a point lm below the surface of water = atmospheric pressure ( = Question 1.013 .× 10⁵ N M²)+ pressure due to the column of water of height 1 m.
= 1.013 × 10⁵+0.098 × 10⁵
= 1.111 × 10⁵ N m²
Area of the plate = 10 × 10 = 10² m²
∴ Total thrust on the plate = Pressure × Area = (1.111 × 10⁵) × 10²
= 1.111 × 10⁷ N.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 7 World of Microbes offer valuable context and analysis.

WBBSE Class 8 Science Chapter 7 Question Answer – World of Microbes

Multiple Choice Questions & Answers : (1 mark for each question)

Question 1.
Microbes have survived in the earth over —
i) 5.8 billion years
ii) 2.8 billion years
iii) 8.8 billion years
iv) 3.5 billion years
Answer:
iv) 3.5 billion years

Question 2.
Microbes grow better in —
i) darker place
ii) direct sunlight
iii) water
Answer:
i) darker place.

Question 3.
A protozal disease —
i) tuberculosis
ii) hydrophobia
iii) malaria
iv) mumps
Answer:
iii) malaria

Question 4.
Microbes are of —
i) three types
ii) four types
iii) two types
iv) five types
Answer:
ii) four types

Question 5.
Vaccine of hydrophobia was discovered by —
i) Robart Koch
ii) Louis Pasteur
iii) Ehrenberg
Answer:
ii) Louis Pasteur

Question 6.
Through sneezing spreads —
i) Ringworm
ii) Malaria
iii) Allergy
iv) Tuberculosis
Answer:
iv) Tuberculosis

Question 7.
A fungal disease —
i) Ring worm
ii) Cholera
iii) Pneumonia
iv) Kaja azar
Answer:
i) Ringworm.

Question 8.
Microbes are found in —
i) water
ii) air
iii) soil
iv) everywhere
Answer:
iv) everywhere

Question 9.
If by mistake some one consumes colourful fungi, lie or she will suffer from —
i) Typhoid
ii) Polio
iii) enteric disease
iv) malaria
Answer:
iii) enteric disease

Question 10.
Baoteria, Virus P, Fungus P can convert the alcohol to vinegar.
Answer:
Bacteria.

State whether True or False : (1 mark for each question)

1) Virus possess DNA or RNA surrounded by protein coat.
2) Tuberculosis is a water-borne disease.
3) Microbes cannot survive in direct sunlight.
4) Microbes can take food from hot foodstuff.
5) Virus is a microbe.
6) The microbes can grow better at 70° – 80°C temperature.
7) Algae can synthesise their own food.
8) Ringworm is a protozoal disease.
9) Some colourful fungi are poisonous.
10) Chlamydomonas is multicellular.
11) Dry places are ideal for growth and survival of the microbes,
2) All viruses are parasites and disease-causing agents.
Answer:
1) true
2) false
3) true
4) false
5) true
6) false
7) true
8) false
9) true
10) false
11) false
12) true

Fill in the blanks : (1 mark for each question)

1) The living organisms that cannot be seen with naked eyes are called ……………
2) Microbes have survived over ……………years in the earth.
3) The total mass of microbes is …………… of the mass of all living organisms.
4) NearIy…………… of oxygen inhaled by us come into the atmosphere from the microbes.
5) Microbes cannot survive in direct ……………
6) Microbes collect their food from ………….. and ………….. organic substances.
7) The organisms that can produce their own food are ……………
8) The …………..bacteria can grow at 100°C.
9) …………… are structurally very simple and smallest among all living organisms.
10) In Bacteria ………….. is present instead of true nucleus.
11) The description of bacteria was given for the first time by ………….. in 1683.
12) The term bacteria was first used by ………….. in 1828.
13) Presently, bacteria are placed in kingdom ……………
14) Name of a colonial algae is …………..
15) From the research of ………….. we come to know the possible existence of a virus that causes small pox.
16) ………….. are acellular.
17) ………….. bacteria live in the intestine of humans for their food and shelter.
18) The interrelationship between host and microbes are called …………..
19) ………….. is prepared from sugar or starch by using yeast.
20) When a sample of warm milk at a temperature of ………….. is mixed with ………….. present in curds, vigorous growth of bacteria takes place.
Answer:
1) microbes
2) 3.5 billion
3) 60%
4) 50%
5) sunlight
6) dead, decaying
7) algae
8) thermophilic
9) bacteria
10) spiral DNA.
11) Antonyh von Leauwen hock,
12) Ehrenberg
13) Monera
14) Volvox
15) Edward Jenner
16) virus
17) E. coli
18) parasitism
19) Alcohol
20) 37°C, Lactobacillus.

Match the following : (1 mark for each question)

a) Match the column A with column B.

A	B
1) Malaria 2) Thermophilic bacteria 3) Louis Pasteur 4) Ehrenberg 5) Lactic acid 6) The term ‘virus’ means 7) Multicellur 8) Bacteria is placed in	a) grow and survive at 100°C. b) first used the term bacteria. c) mosquito-borne disease d) discovered vaccine of hydrophobia e) poison f) present in curd g) kingdom of Monera h) Spirogyra.

Answer:
1) Malaria, mosquito borne disease.
2) Thermophilic bacteria grow and survive at 100°C.
3) Louis Pasteur discovered vaccine of hydrophobia.
4) Ehrenberg first used the term bacteria.
5) Lactic acid present in curd.
6) The term virus means poison.
7) Multicelluar — Spirogyra.
8) Bacteria is placed in Kingdom of Monera.

Very Short Questions & Answers : (1 mark for each question)

Question 1.
What are microbes?
Answer:
Besides plants and animals, many other living organisms remain scattered around us which are not seen with naked eyes, these are called microbes.

Question 2.
For how many years microbes are there in the earth?
Answer:
Microbes have survived over 3.5 billion years in the earth.

Question 3.
How many microbes are there in the soil under our feet?
Answer:
Near about 10 lakhs of microbes are there in the soil under our feet.

Question 4.
How many microbes are there in 1g of soil?
Answer:
It is speculated that about 100 crore microbes are present in 1g of soil.

Question 5.
What type of place is ideal for the growth of microbes?
Answer:
Damp and swampy places are ideal for the growth of microbes.

Question 6.
Name some microbes who find shelter in other organisms?
Answer:
Microbes who find shelter in other organisms are virus, bacteria (Monera), fungi and protozoa etc.

Question 7.
Where can we find the thermophilic bacteria?
Answer:
The thermophilic bacteria are found in hot springs and hydrothermal vent.

Question 8.
What is the shape of Bacteria?
Answer:
Bacteria have various shapes — like a eamma, rod, spiral and rounded.

Question 9.
What is present in bacteria instead of true nucleus?
Answer:
Spiral DNA (nucleoid) is present instead of true nucleus.

Question 10.
Who gave description of bacteria first time?
Answer:
Anatomy von Leeuwen hock.

Question 11.
Who discovered vaccine of hydrophobia?
Answer:
Louis Pastur, a French scientist discovered vaccine of hydrophobia.

Question 12.
Who discovered two human pathogens Cholera and Tuberculosis?
Answer:
German Scientist Robert Koch.

Question 13.
Who first used the term bacteria?
Answer:
The term bacteria was first used by Ehrenberg in 1828.

Question 14.
How many cells are there in Protozoa?
Answer:
Protozoa are unicelluar.

Question 15.
Name the locomotary organs of protozoa.
Answer:
Their locomotary organs are pseundopodia, whiplash flagella or hair-like cillia.

Question 16.
What is hyphnae?
Answer:
The small filamentous part of a fungi is called hyphae.

Question 17.
When a mycelium is formed?
Answer:
The large number of hyphae together form a mycelium.

Question 18.
Where Algae are found?
Answer:
Algae are acquatic, they are found in marine and fresh water.

Question 19.
Why Algae can synthesist their own food?
Answer:
Various types of chloroplasts are present in algae so they can synthesise their own food.

Question 20.
What the term ‘Virus’ means?
Answer:
The term ‘ Virus’ is actually a Latin word which means poison.

Question 21.
Name a unicellular and a multicellular algae.
Answer:
Chlamydomones is a unicellular algae and Sprigyra is a multicellular algae.

Question 22.
Who discovered the vaccine of small pox?
Answer:
Edward Jenner.

Question 23.
Write name of three Bacterial disease.
Answer:
Tuberculosis, Whooping Cough, Cholera.

Question 24.
Write name of three virul diseases.
Answer:
Influenza, Mumps, Pox.

Question  25.
Write name of three Protozoal diseases.
Answer:
Amoebiasis, Malaria, Giardiasis.

Question 26.
Write name of three Fungal diseases.
Answer:
Ringworm, Allergy, diseases of nose throat and lung.

Question 27.
Which crops increase nitrogen in soil?
Answer:
Leguminous crops like pulses, pea etc increase nitrogen in soil.

Question 28.
Which vitamin helps to synthesise haemoglobin in RBC?
Answer:
Vitamin B₁₂.

Question 29.
Which bacteria live in the nodule of the leguminous plant?
Answer:
Symbiotic bacteria like Rhizobium live in the root nodules of the leguminous plants.

Question 30.
What is symbiosis?
Answer:
Sometimes organisms live together for sharing their nutrition, this association is known as symbiosis.

Question 31.
How majority of the plants take nitrogen?
Answer:
Majority of the plants take nitrogen in the form of NO₃ or NH₄.

Question 32.
Name some organisms which fix atmospheric nitrogen directly.
Answer:
Clostridium, Azotobacter and a few cyanobacteria fix atmospheric nitrogen directly.

Question 33.
What is ammonification?
Answer:
After the death of plants and animals, the protein components are broken down into ammonia, this process is called ammonification.

Question 34.
What is Nitrification?
Answer:
Ammonia is converted into nitrate and nitrite by nitrifying bacteria, namely Nitrosomonas orNitrobacter, this process is called Nitrification.

Question 35.
How jute fibre can be separated?
Answer:
The jute fibre can be separated easily by decomposing pectin which is present in the cell wall of jute.

Question 36.
Which bacteria is present in curd?
Answer:
Lactobacillus bacteria.

Question 37.
Who first discovered an antibiotics?
Answer:
Alexander Flemming first discovered an antibiotic in the year 1928.

Question 38.
Name some antibiotics?
Answer:
Penicillin, Streptomycin, Chloromycetin. Ampicillin etc.

Short Questions & Answers : (2 marks for each question)

Question 1.
What is Staining?
Answer:
Sometimes to identify microbes under microscope we use various coloured substances for their identification, these coloured substances are known as stain and the process is called Staining.

Question 2.
What are parasitism?
Answer:
Some of the microbes that enter our body through various agents finally reach inside the cell. This interrelationship between host and microbes are called parasitism.

Question 3.
What are antigens?
Answer:
When any microbe (virus, bacteria) enters our body, many harmful compounds eminateu from their whole body or body surface and mix with our body fluids, they are called antigens.

Question 4.
What are antibody?
Answer:
A type of compound gets synthesised in our body in order to destroy the antigens. The compounds are protein in nature and are referred to as antibody.

Question 5.
What is Immunity?
Answer:
The power of resistance of any organism against infection is called Immunity.

Question 6.
What are antibioties?
Answer:
Some organic compounds produced by some bacteria and fungi under the process of grotli of other bacteria or even kill them. Many life saving drugs manufactured through different processes of purification and chemical changes of these compounds, these life-saving drugs are called antibiotics.

Question 7.
What is symbiosis, define?
Answer:
Sometimes organisms live together for sharing their nutrition. In the association of nodule-forming bacteria and root of leguminous plant in the association of E.ccoli and humans, both the bacteria never harm the host both are mutually benefited. This type of association is known as symbiosis

Long Questions & Answers : (3 marks for each question)

Question 1.
Write four characteristics of microbes.
Answer:

• Microbes are found almost everywhere.
• Damp and swampy places are ideal for their growth and survival.
• They collect their food from dead and decaying organic substances, from different organs, tissues or cells of animals in which they take shelter. Some are able to synthesise their own food.
• Generally, the microbes can grow better at 25tvC to 38°C.

Question 2.
Write some characteristics of Bacteria.
Answer:

• Bacteria are structurally very simple and smallest among all living organisms.
• They have various shapes – like a comma, rod, spiral and rounded.
• Spiral DNA (nucleoid) is present instead of true nucleus.
• Membraneless ceil organelle like ribosome is present.

Question 3.
Write some characteristics of Protozoa.
Answer:

• Protozoa are unicellular and placed under protista having one or more nucleus.
• They are variously shaped
• They live freely as a single entity or in a colony, some live in the host body and cause disease.
• Their locomotory organs are pseudopodia, whiplash flagella or hair-like cilia.

Question 4.
Write some characteristics of Fungi.
Answer:

• Body of Fungi is not differentiated into root, stem and leaves.
• They are unicellular or multicellular filamentous.
• They have cell wall, nucleus and other organelles but are devoid of chloroplast. Hence, they cannot synthesise their food.
• Cell wall is not similar to the cell wall of higher plants.
• They can survive in water, land either in presence or in absence of sunlight.

Question 5.
Write some characteristics of Algae.
Answer:

• Body of Algae is not differentiated into root, stem and leaves.
• They are unicellular or multicellular.
• Their cell contains cell wall, nucleus, other organelles and chloropiasts, so they can synthesise their own food.
• They requere sunlight for their growth.
• All are acquatic (marine and fresh water).

Question 6.
Write some characteristic features of virus.
Answer:

• Viruses are acellular.
• They have no boundary wall, cytoplasm or nucleus instead they possess a nucleic acid (DNA or RNA) surrounded by protein coat.
• All are parasites and disease-causing agents. They behave as inert particles, only when they enter the body of the host they behave like living being.

Question 7.
What is parasitism, define?
Answer:
Some of the microbes that enter our body through various agents finally reach inside the cell. They cannot survive alone, they depend on the host, organ or cell for their food and shelter. When they grow inside the host cell, they inhibit the normal function of the cell and hamper the physiological process of the host. It may cause death of the host. This interrelationship between host and microbes are called parasitism.

Question 8.
What is saprophytism?
Answer:
Many microbes grow’ on dead animals and help in the decay of organic matter. They decompose the organic mater into simpler compounds with the help of secreted enzymes. This helps plants consume these as nutrients. Numerous bacteria and fungi secrete digestive juices on the substratum, on which they grow end obtain their food. This process is known as saprophytism.

Question 9.
Suggest five ways in which we can preserve food?
Answer:

• By keeping food products in airtight containers (Canning).
• By mixing salt with fish, meat and fruits (salting).
• Pieces of mango, lemon onion etc can be preserved by adding vinegar (Pickling)
• Food can be preserved by storing at low temperature (Refrigeration)
• Milk can be preserved by pasteurization.

Question 10.
What is vaccination or Innnunitsation? Name some diseases which can be prevented by Vaccinations.
Answer:
Dead or weak but live microbe or weakly toxic substances released from the body of microbes are administred in a human being in a definite dose.

The defence mechanism become; activated in the individual against any particular infectious disease, in advance. This process is called Vaccination or Immunisation, it has been possible to control spreading of many diseases like typhoid, Tetanus, Polio and Diphtheria by the use Vaccines.

Question 11.
Explain some ways, of treatment of waste.
Answer:

• Any untreated waste like human faeces or untie always bear some risk for human health. Some bacteria Living in less oxygenated atmospheres are able to break down these wastes to nitrate and phosphate. They reduce the chance of infection and also increase soil fertility.
• in countries like India and China, Methanogenic bacteria degrade human or animal faces, vegetable peels and produce methane gas. They act as substitutes for coal or Kerosene.
• Some algee are being used in space shuttles to clean the air.