Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 4 Occurrence of Carbon and its Compounds in Nature offer valuable context and analysis.
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
CNG is used as –
i) cooking gas
ii) fuel of vehicles
iii) generation of electricity
iv) preparation of bricks
Answer:
ii) fuel of vehicles
Question 2.
Domestic, industrial and agricultural wastes are used to produce-
i) biomass
ii) bio fuel
iii) bio gas
iv) steam
Answer:
iii) bio gas
Question 3.
Combustion of fossil fuel may cause-
i) global warming
ii) acid rain
iii) respiratory diseases
iv) ail of the above
Answer:
iv) all of the above
Question 4.
At normal temperature and 60 atmospheric pressure Carbon dioxide is converted to –
i) liquid
ii) solid
iii) gas
iv) none of the above
Question 5.
Carbon dioxide is –
i) lighter than air
ii) blue in colour
iii) completely soluble in water
iv) colourless
Answer:
iv) colourless
Question 6.
Polythene is used in making –
i) carry bags
ii) buckets
iii) cup plate
iv) cloth
Answer:
i) carry bags
Question 7.
Teflon is –
i) transparent
ii) flexible
iii) poor conductor of slectricity
iv) opaque
Answer:
iii) poor conductor of slectricity
Question 8.
PVC is used to prepare –
i) nonstick utensils
ii) raincoat
iii) clothes
iv) cup plate
Answer:
ii) raincoat
Question 9.
Of total mass of human body carbon is-
i) 5 0 %
ii) 30 %
iii) 10 %
iv) 80 %
Answer:
i) 50 %
State whether True or False : (1 mark for each question)
1. Diamond is harder and denser than graphite.
2. 60 % of carbon dioxide generated through human activitiesis absorbed by the oceans.
3. Graphite is not a conductor of electricity.
4. Fullerenes are not macromolecules.
5. Coal is used as a fuel of vehicles.
6. Snails and corals absorb carbon dioxide dissolved in water and form their shells.
7. Some anaerobic bacteria can convert carbon monoxide to organic compounds.
8. CNG is used for cooking.
9. Taptapani hot spring is situated in Odissa.
10. Bio-diesel is prepared from vegetable oils or animal fat.
11. Polythene is not insulator of slectricity.
12. Methanogenic bactria in wetlandsproduce methane.
Answer:
1.true
2. false
3. false
4. true
5. false
6. true
7. true
8. false
9. true
10. true
11. false
12. true
Fill in the blanks : (1 mark for each question)
1. Of the entire mass of human body, carbon comprises ______ of the total mass.
2. In the shell of snail or other marine animals there is ______.
3.Synthesis of diverse organic molecules by living organisms is known as ______.
4. Methane is one of the ______ gas.
5. In room temperature heat conductivity of diamond is greater than any other ______.
6. Graphite is ______ of electricity.
7. The symbol of fullerene molecule is ______.
8. Temperature of the centre of earth is ______.
9. The ______ oil can be used directly in diesel generators or engines without purification.
10. Neutrons and protons are bound in a nucleus by an energy called ______.
11. A target is set to generate ______ megawatt of electricity by 2032.
12. ______ is a pungent-smelling corrosive gas.
13. Urea is used as the major ______ fertiliser.
14. Temperature of solid carbon dioxide is ______.
15. The increase of temperature of the atmosphere due to green house effect is called ______.
16. ______ is produced through the digertion of organic waste in absence of air.
Answer:
1.50 %
2. Calcium Carbonate
3. biosynthesis
4. green-house
5. metal
6. goodconductor
7. C60
8. 6000° C
9. Jatropha
10. Nuclear energy
11. 63,000
12. Sulphur dioxide
13. nitrogenous
14. 78° C
15. global warming
16. Biogas.
Match the following : (1 mark for each question)
a) Match the column A with column B.
| Column A | Column B |
| a) Teflon is used | i) water-resistant fibre. |
| b) Polythene is used to | ii) finished fuel. |
| c) Nylon is a | iii) energy. |
| d) Carbon dioxide is | iv) make carry bags. |
| e) Carbon dioxide is used | v) is still hot. |
| f) Bio gas is useci as a | vi) less amount of heat. |
| g) The core of the earh | vii) a colourless gas. |
| h) The refining of coal | viii) to prepare non-stick utensils. |
| i) Low-grade coal produces | ix) to produce urea. |
| j) Fuels are the sources of | x) is called coal washing. |
Answer:
a) Teflon is used to prepare non-stick utensils.
b) Polythene is used to make carry bags.
c) Nylon is a water-resistant fibre.
d) Carbon dioxide is a colourless gas.
e) Carbon dioxide is used to produce urea.
f) Bio gas is used as a finished fuel.
g) The core of the earh is still hot.
h) The refining of coal is called coal washing.
i) Low-grade coal produces less amount of heat.
j) Fuels are the sources of energy.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
Name two elements which have allotropy forms.
Answer:
Carbon, Sulphur can have more than one allotrope.
Question 2.
How many carbon atoms exist in fullarene?
Answer:
60 or 70 carbon atoms exist in fullerene.
Question 3.
In which industry fullerene is used?
Answer:
In electronics and medicine industry fullerene is used..
Question 4.
In which form carbon can make mark on a paper?
Answer:
Graphite can make mark on a paper.
Question 5.
In which form carbon is a good conductor of heat and electricity?
Answer:
Gas Carbon is a good conductor of heat and electricity.
Question 6.
Which form of carbon looks like a football?
Answer:
Fullerene (C60).
Question 7.
Write name of two green house gases.
Answer:
CO2 and methane are two green house gases.
Question 8.
What compound CO gas makes with Hacmoglobin?
Answer:
Carboxi haemoglobin.
Question 9.
Which form of carbon dissolves in organic solvent?
Answer:
Fullerene dissolves in organic solvent.
Question 10.
What is water gas?
Answer:
The mixture of CO and H2 is called water gas.
Question 11.
Which form of carbon can cut glass?
Answer:
Diamond can cut glass.
Question 12.
Which form of carbon is called ‘a bucky ball’?
Answer:
Fullerence.
Question 13.
If diamond is strongly heated in presence of air what is produced?
Answer:
Carbon dioxide gas is produced.
Question 14.
Which oxide of carbon is poisonous?
Answer:
Carbon monoxide (CO).
Question 15.
What is bourt?
Answer:
Black coloured not transparent diamond is called bourt.
Question 16.
What is producer gas?
Answer:
The mixture of carbon monoxide and nitorgen (CO + N2).
Question 17.
What is ‘non-biodegradable’polymers?
Answer:
The artificial polymers made by man are called ‘non-biodegradable’ polymers.
Question 18.
What is Dry Ice?
Answer:
Solid carbon dioxide is called Dry lce..
Question 19.
What is bio fuel?
Answer:
Bio fuel means the fuel produced from assimilated food in plants and microbes.
Question 20.
What is coal washing?
Answer:
The refining of coal is called coal washing.
Short Questions & Answers : (2 marks for each question)
Question 1.
What is allotropes?
Answer:
When an element can be found in more than one physical form, then the different physical form in which the element sxists are called its allotrope.
Question 2.
What are the allotropes of carbon?
Answer:
The allotropes of carbon are commonly divided into two categories-1. crystalline and 2. amorphous.
Crystalline “rms of carhon are-i) diamond, ii) graphite iii) fullerene. A morphou forms of carbon are- i) charcoal, ii) lamp black, ifi) coke. (v) gas carbon.
Question 3.
What is Coal Washing?
Answer:
Lifting Coal from coal mines and purifying it by different methods is called coal Washing. As a result a low-smoke and lowash coal can be produced separating various impurities present in coal.
Question 4.
What is Water gas and Producer gas?
Answer:
Mixture of Carbon monoxide and Hydrogen gas is called water gas C ± H2 O → Mixture of Carbon monoxide and Nitrogen gas is called producer gas. When limited air is passed over extremely heated coke then we get C ± N2 O →
Question 5.
Name some alternative sourses of energy apart from traditional fuels.
Answer:
Some alternative sources of energy apart from traditional fuels are-i) Solar energy, ii) Wind energy, iii) Geo-thermal energy, iv) Bio-fuels, v) Atomic energy.
Long Questions & Answers : ( 3 marks for each question)
Question 1.
Write the physical properties of diamond.
Answer:
i) Diamond is a transparent, colourless solid. Most naturally– occuring diamonds contain small amount of impurities. ‘vhich impart colour to them.
ii) Diamond bends the light rays passing through it as it has a high refractive index of 2.47 . It is because of this property that properly cut and polished diamond sparkles brightly.
iii) It has a high density of 3.5 g / cm3.
iv) It has a high melting point of about 3500° C.
v) It is the hardest natural substance. Oniy a diamond can cut another diamond.
vi) It is a poor conductor of heat and electricity.
Question 2.
Write uses of diamond.
Answer:
a) As properly cut and polished diamond sprerkles brightly, it is used in jevellery:
b) Diamond absorbs harmiful radiation. Hence, it is used in space satellites to make radiationproof windows.
c) Because of its hardness, diamond tipped tools are used for cutting and drilling of rocks.
d) Diamond is used to cut glass. :
Question 3.
Write physical properties of graphite.
Answer:
Question 4.
How is Biogas and Bio-fuel produced?
Answer:
Biugas is produced through the digestion of crganic waste in absence of air. It can be used as a finished fuel. In this anaerobic digestion, mainly methane is produced. so this is called biological methane production or bio-methanetion. Domestic, industrial and agricuitural wastes are ured in this process.
Biofuel means the fuel produced from assimiiated food in plarts and miciobes. In sur country production of biofuel means the cultivation of Jatropha plants and processing of oil from its seeds to prepare bio-diesel. The Jatropha oil can be used directly in diesel generators or engines without purification.
Question 5.
Write the physieal properties of Carbon dioxide.
Answer:
Question 6.
Write some uses of Carbon dioxide.
Answer:
a) Preparation of urea : Nitrogenous fertilisers are needed for good crop. Urea is used as the nitrogenous fertiliser. Urea is produced by reacting Carbon dioxide with ammonia.
b) Production glass: Modern civilization is unbelievable without glass. Soda(Na2 CO3) is required for preparation of glass. Vast amount of carbondioxide is required to manufacture glass.
c) For making fire-extin guishter and to prepare solid carbon dioxide.
To prepare different soft-drinks and to extinguish fire, carbon dioxide is needed though it can not be used for fire caused by oil or metal. If carbon dioxide is cooled to -80° C, it becomes a solid. Solid carbon dioxide is called dry-ice. It is a useful refrigerating solid as it does not wet. It is used for food presevation.
Question 7.
How can we maintain the balance of CO2 and O2 in atmosphere?
Answer:
i) We have to preseve our forests and plant trees in cities and towns so that plant absorbs CO2 from atomsphere will be converted in O2 and the balance would be maintained.
ii) Everyday we burn fossil fuels and generate millions of tonnes of CO2 that reaches atmosphere. We have to reduce the use of fossil fuel and increase the use of natural gas, hydrogen etc in vehicles. This will prevent the increase in CO2 level in the atmosphere.
iii) To produce electricity we should have to decrease the use of coal and increase the use of solar energy, geo-therma! energy, nuclear energy and tidal energy to produce electricity, to stop the increase of CO2 level in atmosphere.
Question 8.
What is green house effect?
Answer:
Gas molecules in the atomsphere can not absorb the solar infrared, so it heats up the earth. Some of the absorbed energy gets dissipated through materials in the surroundings. The rest of the energy is re-emitted by the earth. Molecules of some gases in the atomsphere carbon dioxide (CO2), water vapour (H2O), nitrous oxide (N2O), methane (CH4), ozone (O3) and the chlorofluorocarbons-absorb this low-energy infrared radiation emitted by the earth. As a result some heat cannot reach the outer space and gets trapped in the atmosphere. This phenomenon is known greenhouse effect.
Question 9.
What is global warming?
Answer:
With the increased industrialisation, burning of fuels in homes and rising population more CO2 is released. On the other hand, the decreasing vegetation and deforestation is leading to less CO2 utilisation in photosynthesis. The level of CO2 in the atmosphere is increasing steadily for the past three hundred years. Scientists are worried that someday in near future the green-house effect due to CO2 will be so large that it will increase the temperature of the atmosphere. Such a possible warming effect is called global warming that may even melt the polar ice caps.
Question 10.
Write the Hazardous effects on environment due to combustion of fossil fuels.
Answer:
1. From the combustion of fuels like wood, coal, petroleum etc. the unburnt carbon particles are spread in the environment. These cause respiratory disese like Asthma.
2. The incomplete burning of such fuels produces carbon monoxide which is a poisonous gas. So burnig of cola or other carbonaceous fuel in a closed room is very harmful and can even cause death.
3. CO2 mixes with air on burning most of the fuels. It is increase in CO2 in the atomosphere that is held responsible for global warming.
Question 11.
What are polymers define. Write two main reasons for the use of different polymers.
Answer:
Polymers are compounds make from smaller units. Many molecules, similar or different, combine chemically to form such chain-like long molecules. The long chain molecule formed by the joining of a large number of monomers is called polymer. Cotton, silk, wool and jute are naturallyoccuring polymers. Polyethylene, polystyrene, poly vinyl chloride (PVC) and bakelite are synthetic polymers. These are called plastics.
Two main reasons for the use of different polymers in place of the previously used substances are-(i) The life of artificial polymers is longer (ii) during preparation of different objects they can be moulded as necessary.
From text book (page-149-150)
Fill in the blanks given below:
(a) FbCO3 + 2 HNO3 = ________ + CO2 + H2 O
(b) CaCO3 + 2 HCl = ________ + CO2 + H2 O
(c) Na2 CO3 + H2 SO4 = _____ + CO2 + H2 O
(d) MgCO3 + + = MgCl2 + CO2 +
(e) NaHCO3 + HCl = Nacl + ________ + H2 O
Answer:
(a) PbCO3 + 2 HNO3 = Pb(NO2)2 + CO2 + H2 O
(b) CaCO3 + 2 HCl = CaCl2 + CO2 + H2 O
(c) Na2 CO3 + H2 SO4 = Na2 SO4 + CO2 + H2 O
(d) MgCO3 + 2 HCl = MgCl2 + CO2 + H2 O
(e) NaHCO3 + HCl = NaCl + CO2 + H2 O
Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 3 Know About Some Common Gases offer valuable context and analysis.
Hands-on Activity :
Answer (See Text-book, page-124)
Answer:
Answer (See Text-book, page-125)
Fill up the blanks (See Text-book, page-131-132)
Answer :
A. 1. Zn + dilute H2 SO4 → ZnSO4 + H2
2. Mg + dilute HCl → MgCl2 + H2
3. Fe + dilute H2 SO4 → Fe2(SO4)3 + H2
4. Al + dilute HCl → Al2 Cl2 + H2
B. 1. Na + H2 O (cold water) → NaO + H2
2. Ca + H2 O (cold water) → CaO + H2
3. Mg + H2 O (boiling water) → MgO + H2
4. Al + H2 O (boiling water) → Al(OH)2 + H2
5. (red hot) Fe + H2 O(. steam) → Fe2 O3 + H2
C. 1. Zn + NaOH (concentrated solution) → Na2 ZnO2 + H2
2. Al + NaOH (concentrated solution) + H2 O → NaAlO2 + H2
Si + 2 NaOH + H2O = Na3 SiO3 + 2 H2
D. Water acidified with sulphuric acid (H2O) → O2 + H2
E. CaH2 + 2H2O → Ca(OH)2 + H2
LiH + H2O → LiOH + H2
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
Catalyst enzyme breaks down hydrogen peroxide into-
i) oxygen
ii) hydrogen
iii) water and oxygen
iv) water and hydrogen
Answer:
iii) water and oxygen
Question 2.
Number of isotopes in oxygen-
i) three
ii) four
iii) two
iv) five
Answer:
i) three
Question 3.
Freczing point of liquid oxygen is–
i) -183° C
ii) -100° C
iii) -118° C
iv) -218° C
Ans:
iv) -218° C
Question 4.
Oxygen is-
i) colourless
ii) odourless
iii) tasteless
iv) all of the above
Answer:
iv) all of the above
Question 5.
Alkaline potassium pyrogallate solution absorbs oxygen and turns-
i) white
ii) brown
iii) red
iv) green
Answer:
ii) brown
Question 6.
Water is made up of –
i) hydrogen
ii) oxygen
iii) hydrogen and oxygen
Answer:
iii) hydrogen and oxygen
Question 7.
Which of the following is true-
i) hydrogen is the lightest gas
ii) hydrogen is heavier than air
iii) oxygen is lighter than air
iv) hydroge is equal to air in weight
Answer:
i) hydrogen is the lightest gas
Question 8.
Which of the following is not fertilizer?
i) urea
ii) ammonium sulphate
iii) ammonium nitrate
iv) atomic oxygen
Answer:
iv) atomic oxygen
Question 9.
Which of the following is chemical propertiy of hydrogen?
i) not inflammable
ii) inflammable
iii) formation of oxide
iv) not diatomic
Answer:
ii) inflammable
Question 10.
Which of the following material is required for preparation of hydrogen gas?
i) manganese dioxide
ii) solution of hydrogen peroxide
iii) impure zine granules
iv) pure zinc granules
Answer:
iii) impure zine granules
State whetherTrue or False : (1 mark for each question)
1. Oxyzen is slightly heavier than air:
2. Atomic oxygen is a powerful oxidizing agent.
3. Hydrogen is indispensable in manufacturing nitric acid.
4. Oxygen is completely soluble in water.
5. Oxygen can combine directly with most of the metals and non-metals.
6. Hydrogen is heavier than air.
7. Hydrogen is used in production of ammonia.
8. Hydrogen gas does not help in burning.
9. A woulfe bottle is necessary for preparation of oxygen.
10. Manganese dioxide is required for preparation of hydrogen.
Answer:
1. true
2. true
3. fa’se
4. false
5. truc
6. false
7. true
8. true
9. false
10. false
Fill in the blanks : (1 mark for each question)
1. Hydrogen is necessary in many ___ industries.
2. The industrial world gets its requirement of oxygen from _____.
3. Oxygen-dependent processes do generate more ______ but there are some disadvantages.
a. Aluminium reacts with oxygen and produce ______.
5. At normal or low temperature Au, Ag can absorb______.
6. Delute solution of hydrogen is required for preparation of ______.
7. Colourless nitric oxide gas is oxidized to brown _______ in contact with oxygen.
8. The main use of hydrogen is in the production of _____.
9. Air is about 14.4 times havier than ______.
10. Hydrogen does not help in burning but it is ______.
11. Platinum can absorb ______ gas at normal temperature.
Answer:
1. chemical
2. air
3. energy
4. aluminium oxide
5. oxygen
6. oxygen
7. nitrogen dioxide
8. ammonia
9. hydrogen
10. inflammable
11. hydrogen
12. chemical
Match the following : (1 mark for each question)
a) Match the column A with column B.
| Column A | Column B |
| a) Oxygen is slightly | i) manufacturing nitric acid. |
| b) Atomic oxygen is a powerful | ii) from vegetable oils. |
| c) Alkaline potassium pyrogallate solution | iii) insoluble in water. |
| d) Oxygen is indespensable in | iv) oxidizing agent. |
| c) hydrogen is used to produce edible fats | v) is 218°C |
| f) Hydrogen is almost | vi) hydrogen is colourless and tasteless. |
| g) Freezing point of liquid oxygen | vii) heavier than air: |
| h) Oxygen is | viii) react with oxygen. |
| i) Under normal coditions | ix) absorbs oxygen and turns blue. |
| j) Aluminium and rine | x) not inflammable. |
Answer:
a) Oxygen is slightly heavier than air.
b) Atomic oxygen is a powerful oxidizing agent.
c) Alkaline potassium pyrogallate solution absorbs oxygen and tums blue.
d) Oxygen is indespensable in manufacturing nitric acid.
e) hydrogen is used to produce sdible fats from vegetable oils.
1) Hydrogen is almost insoluble in water.
g) Freezing point of liquid oxygen is -218° C.
h) Oxygen is not inflammable.
i) Under normal coditions hydrogen is colourless and tasteless.
j) Aluminium and zinc react with oxygen.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
What does the decomposition of H2 O2 produce?
Answer:
Water and oxygen.
Question 2.
What is the chemical symbol of hydrogen?
Answer:
H2
Question 3.
What is the specific gravity of hydrogen?
Answer:
It is the lightest of all gases with a specific gravity of 0.0695 .
Question 4.
How is hydrogen detected?
Answer:
It can be detected by chemical analysis.
Question 5.
Is hydrogen water soluble?
Answer:
No.
Question 6.
What is the specific gravity of oxygen?
Answer:
Specific gravity of oxygen is 1.105
Question 7.
What is the chemical symbol of oxygen?
Answer:
O2
Question 8.
Is oxygen flamable?
Answer:
No. Oxygen alone will not burn.
Question 9.
When the oxygen level in air considered to he dangerous?
Answer:
When oxygen level falls below 16 %.
Question 10.
What element in the air is essential for life?
Answer:
Oxygen.
Short Questions & Answers : (2 marks for each question)
Question 1.
Write two advantages of having oxygen in air.
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy.
Question 2.
What happens when Oxygen reacts with non-metals?
Answer:
Oxygen reacts with non-metals such as carbon. sulphur and phosphorus to form acidic oxides. C + O2 → CO2 \quad S + O2 → SO2
Question 3.
Why oxygen is called acid producer?
Answer:
The non-metals, on combustion with oxygen. produce oxides. These oxides produce acid when they react with water. So these oxides are called acidic oxides.
Question 4.
Mention some metals which absorb oxygen.
Answer:
At normal or low temperature, Au, Ag, Pt. Pb etc. can absorb oxygen. i.e can bind oxygen weakly at their surface. On heating the metal, oxygen is released.
Question 5.
What are the materials required for preparation of oxygen gas from hydrogen peroxide?
Answer:
i) delute solution of hyfrogen peroxide
ii) manganese dioxide
iii) a jute stick
iv) a test tube
v) a test tube holder
Question 6.
What are the materials required for preparation of oxygen gas from sodium peroxide?
Answer:
i) sodium peroxide
ii) distilled water
iii) conical flask
iv) a cork with two holes
v) a dropping funnel
vi) a bent delivery tube
vii) a gas jar
Question 7.
What are the materials required for preparation of oxygen gas from potasium chlorate?
Answer:
i) potassium chlorate,
ii) manganese dioxide free from carbon,
iii) a hard glass test tube,
iv) a cork with a bore,
v) a delivery tube,
vi) a stand,
vii) a gas tough,
vii) a water pot.
Question 8.
What are the materials required for laboratory preparation of hydrogen gas?
Answer:
i) impure zinc ganules
ii) dilute sulphuric acid, distilled water
iii) woulf bottle
iv) thistle funnel
v) bored cocks for wolf bottle
vi) delivery tube
vii) rubber tube
vii) grease.
Long Questions & Answers : (3 marks for each question)
Question 1.
What are the advantages of having oxygen in air?
Answer:
Oxygen is necessary for respiration in living organisms. Oxygen reacts with food and releases energy. Generation of energy from intra-cellular glucose is faster, easier and more efficient with oxygen than without it. It supports combustion. There can be no fire without oxygen.
Question 2.
What vital role oxygen play during respiration of living beings?
Answer:
The role of oxygen in the respiration of animals or plants is extremely vita!. The most important process associated with the respiration of animals is the combination of oxygen i.e combustion of simple ingradient of the carbonaceous food. As a result, the required energy is produced in the body. For example, glucose the simple ingredient of carbohydrate gets oxidised and produce energy.
Question 3.
Write down some absorber of oxygen.
Answer:
Absorber of oxygen are:
i) At normal or low temperature, Au, Ag, Pt, Pb etc. can absorb oxygen, i.e can bind oxygen weakly at their surgace. On heating the metal, oxygen is released.
ii) Alkaline potassium pyrogallate solution absorbs oxygen and turns brown.
iii) Ammoniacal cuprous chloride solution absorbs O2 gas quickly and turns blue.
Question 4.
Write some uses of oxygen.
Answer:
i) Oxygen is used in breathing support systems by patients who cannot get enough oxygen from air due to some health problems.
ii) Oxygen is used to remove the impurities of crude iron. In this way, millions of tonnes of steel are produced.
iii) Oxygen is indepensable in manufacturing nitric acid (HNO3) and sulphuric acid (H2 4).
Question 5.
Write the way of preparation of oxygen in laboratory with the equation.
Answer:
In laboratory Oxygen can be prepared by heating together four parts of potassium chlorate and one part of manganese dioxide. Manganese dioxide acts as the catalyst. It is not consumed in the reaction. It only help potassium chlorate to decompose faster and at lower temperature. The equation of the reaction for such production of oxygen is-
2 KClO3 + [MnO2] → 2 KCl + 3 O2 + [MnO2]
Question 6.
Write some use of hydrogen.
Answer:
a) Hydrogen is used to produce ammonia, which is use in the production of urea fertiliser.
b) It is used to produce various petrochemicals.
c) For the production of hydrogenated vegetable oils, we need hydrogen.
Question 7.
Write some physical properties of oxygen.
Answer:
Some properties of oxygen are-
Question 8.
Write two physical properties and two chemical properties of IIydrogen.
Answer:
Two physical properties of Hydrogen are-
1) Under normal conditions, hydrogen is colourless odourless. tasteless gas.
2) Hydrogen is the lightest gas. Air is about 14.4 times heavier than hydrogen.
Two chemical properties of Hydrogen are-
1) Combustibility: Hydrogen does not help in burning but it is inflammable. If a mixture of hydrogen and oxygen is burit into flame. steam is produced
2 H2 + O2 → 2 H2 O
2) Reduction: Hydrogen has special attraction for oxygen. Hydrogen acts as reducing agent for its high affinity towards oxygen. Reddish-brown copper is produced by reduction of hot cupric oxide by a current of hydrogen gas. Hydrogen is oxidised to water
CuO + H2 → Cu + H2 O.
Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 5 Analysis of Natural Phenomena offer valuable context and analysis.
Fill up the blanks : (See Text Book Page 172)
| Name of the disease | How transmitted | Responsible germ | Means to avoid the disease |
| 1. Cholera | Uncovered food unclean environment | vibrio cholera | taking pure food & drink |
| 2. Maleria | biting of mosquito | Plasmodium vivax | avoid mosquito biting |
| 3. Plague | biting of rats | Yersinia pestis | avoid rat biting |
| 4. AIDS | body fluid & mucous | HIV virus | consciousness |
| 5. Kala Azar | carrier sand fly | Leishmania donovani | consciousness |
Write down what problems may be faced for the absence of proper food habits arid right life style.
| Food habit and life style | Problems likely to be faced |
| 1. Intake of excess carbohydrate | risk of heart disease |
| 2. Intake of excess carbohydrate | risk of diabetes |
| 3. Staying awake at night and insufficient sleep | headache, blood pressure |
| 4. Working with computer for long duration without interruption | spondylities, headache |
| 5. Smoking and intake if intoxicating substances | risk of cancer |
| 6. Excessive use of mobile phone | eye problem, cancer |
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
During thunder the air —
i) vibrates
ii) radiates
iii) attracts violently
Answer:
i) Vibrates
Question 2.
The height of a storm cloud is generally —
i) 3-4 km.
ii) 7-8 km.
iii) 12-13 km.
iv) 17-18 km.
Answer:
iii) 12-13 km.
Question 3.
The lighting conduction is buried at least —
i) 5-6
ii) 10-12 P
iii) 15-18
iv) 20-22 feet deep into the ground.
Answer:
i) 5-6 feet
Question 4.
An epidemic disease is —
i) heart disease
ii) Cholera
iii) headache
iv) skin disease
Answer:
ii) Cholera.
Question 5.
Mosquito-born fatal disease dengue first broke out in Kolkata in the year —
i) 1986-1987
ii) 1982-83
iii) 1990-92
iv) 1963-64
Answer:
iv) 1963-64
Question 6.
Cholera generally causes from —
i) polluted air
ii) polluted water
iii) mosquito
iv) polluted food
Answer:
ii) Polluted water.
Question 7.
The word ‘Malaria’ means —
i) bad water
ii) bad light
iii) bad air
iv) bad soil
Answer:
iii) Bad air
Question 8.
The carrier of Malaria disease —
i) fly
ii) Mouse
iii) Mosquito
iv) lice
Answer:
iii) Mosquito
Question 9.
The medicine of Kalazar was invented by —
i) Galielio
ii) Jagadish chandra Bose
iii) Satyandranath Dtitta
iv) Upendranatk Brahmachari
Answer:
iv) Upendranath Brahmachari
Question 10.
Blood appears in stool in —
i) diarrhoea
ii) smallpox
iii) plague
iv) malaria
Answer:
i) Diarrhoea.
Question 11.
Tuberculosis disease is —
i) waterborne
ii) mosquito-borne
iii) airborne
Answer:
iii) airborne.
Question 12.
Treatment of Tuberculosis is called —
i) HOTS
ii) ACTS
iii) GTSS
Answer:
i) DOTS
Question 13.
Types of Hepatitis are —
i) 2
ii) 3
iii) 4
iv) 5
Answer:
iv) 5
Question 14.
The virus responsible for AIDS disease —
i) IVH
ii) HIV
iii) STS
iv) HVP
Answer:
ii) HIV
Question 15.
Another name of small Pox is —
i) Red plague
ii) Kalazar
iii) white plague
iv) green plague
Answer:
i) Red plague
State whether True or False :(1 mark for each question)
1) Lighting inducts the earth with negative charge.
2) Almost even, day at some part of the world lightning occurs due to thunderstorms which are at least 4,000.
3) The clouds become charged to the friction of clouds or that of the water
4) Generally clouds bring in thunderstorms and rain.
5) Clouds are formed by (lie condensation of tater deoplets.
6) The height of a storm cloud is generally 4-5 km.
7) The water droplets became charged when the clouds rise and come down at the time of storm.
8) The lower edges of tite clouds are inducted with positive charge.
9) There is potential difference between the sky and the earth.
10) If there is potential difference, then lightning may occur between two different cloud or parts of same cloud.
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) The part of the train which is in contact with the electric line is called ________
2) The electrical cells used in radios or torches is called ________
3) In our country, thunderstorms and highlighting seldom occur in ________
4) In an atom (lie electron and the proton are ________ particles.
5) Atoms arc uncharged because the number of protons and electrons in atom is ________
6) If an electron is released from on atom, then the atom becomes a ________
7) In winter if plastic comb is used for combing hair, it acquires ________ charge.
8) ________ is a high-energy electric discharge and it can cause great harm.
9) The flow of electric charge is called an ________.
10) Lighting is that cell in nature which maintains the ________ of electric charge high up in the sky and on earth.
Answer:
1) pantograph
2) dry cell.
3) winter
4) electrically charged
5) equal
6) positive ion
7) negative
8) lighting
9) electric current.
10) potential difference.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
Which cells are called dry cell?
Answer:
The electricals cells used in radios or torches are called dry cell.
Question 2.
What is pentograph?
Answer:
The part of the train which is in contact with the electric line is called pentograph.
Question 3.
Who did experiment on electric spark?
Answer:
Famous scientist Benjamin Franklin.
Question 4.
Which charge is inducted in the lower edges of the clouds?
Answer:
Negative charge.
Question 5.
Which charge is inducted the upper edges of the clouds?
Answer:
Positive charge.
Question 6.
What is the reason that opposite charges accumulate at different edges of the clouds?
Answer:
Potential difference between the sky and the earth. ,
Question 7.
What is the work of lighting conductor?
Answer:
Lighting conductions a device that protects houses and electrical equipments within the house.
Question 8.
What is an epidemic?
Answer:
When hundreds of people die at the same time in every year due to out break of a fatal disease, then that disease is declared as an epidemic.
Question 9.
Write name of some epidemic diseases.
Answer:
Some epidemic diseases are — Malaria, Aids, Influenza, Dengue etc.
Question 10.
Which diseases occur in spring season?
Answer:
The onset of spring sees a spirit in diseases like Measles and Chicken Pox.
Question 11.
Which diseases are common in winter season?
Answer:
Infection of the upper tracts of the respiratory organ is generally common in winter months.
Question 12.
When stomach infection is usually high?
Answer:
Stomach infection is usually high in summer.
Question 13.
What is the cause of Cholera disease?
Answer:
Cholera disease is generally caused from polluted water, uncovered and fly infected food and unhyginenic environment.
Question 14.
Name the germ of disease Cholera.
Answer:
Vibrio cholerae.
Question 15.
Name the germ that female anopheles mosquito carries.
Answer:
Plasmodium vivax or Plasmodium falciparum.
Question 16.
Which mosquito carries the germ of Dengue?
Answer:
A type of mosquito called Aedes Egypt carries the germ of Dengue.
Question 17.
Name the bacteria resposible for Plague.
Answer:
Yersimia pestis is responsible for plague.
Question 18.
Name the type of fly which carries the bacteria from body of rat afflicted with plague.
Answer:
Xenopsyllachopis.
Question 19.
Who invented the vaccine of plague?
Answer:
In 1987, Waldemar Haffkine invented the vaccine of piague in Bombay.
Question 20.
Name the protozoa and the carrier fly which causes Kalazar.
Answer:
The name of protozoa is Leishmania and the carrier fly is Sand fly.
Question 21.
Who invented the vaccine of small pox?
Answer:
British scientist Edward Jenner invented the vaccine of small pox.
Question 22.
What is SARS?
Answer:
It is an epidemic disease Severe Acute Respiratory Syndrome.
Question 23.
What is DOTS?
Answer:
The deadly disease Tuberculosis is prevented through DOT or Directly Observed Treatment.
Question 24.
Name the bacterium resposible for Tuberculosis.
Answer:
Microbacterium tuberculosis.
Question 25.
How many types of Hepatitis is there?
Answer:
There are five types of Hepatitis A, B, C, D and E.
Question 26.
How A and E types of Hepatitis occur.
Answer:
A and E types of infection is caused by contaminated food and water.
Question 27.
How B, C and D type of Hepatitis occur?
Answer:
B, C and D type of Hepatitis infection occurs through the medium of the body fluid and blood of human.
Question 28.
Which day has been declared by WHO as World Hepatitis Day?
Answer:
World Health Organisation (WHO) has declared 28th July as World Hepatitis Day.
Question 29.
What is the full form of AIDS and HIV?
Answer:
Full form of AIDS is – Acquired Immune Deficiency Syndrome and of HIV — Human Immuno dificieancy Virus.
Question 30.
Name some non-infectious diseases which have assumed epidemic dimensions.
Answer:
Some non-infections diseases such as diabetes, hypertension, cancer, mental illness also have assumed epidemic dimensions.
Short Questions & Answers : (2 marks for each question)
Question 1.
What are electrolytes? Give example.
Answer:
The compounds which are able to conduct electricity in a fused state or in a solution, are called electrolytes. Examples of electrolytes are acid or alkyl solution, aqueous solution of a salt, fused Nacl etc.
Question 1.
What is electricity?
Answer:
Electricity is a form of energy and can, thus, be converted to heat, light and even sound. Electricity is caused due to motion of electric charges, which causes electric current to be generated.
Question 2.
What is static electricity?
Answer:
The accumulation of electrical charges on the surface of a material, usually an insulator or a non-conductor of electricity, gives rise to the concept of static electricity. This electricity is, called ‘static’ because there is no current flowing. However, static electricity can cause sparks, shocks or materials to cling to each other.
Question 3.
What is ion? How it can become positive or negative ion?
Answer:
If in an atom number of protons and number of electrons are equal then that atom is called ion. But if the number of protons exceed the number of electrons then the atom become, a positive ion. If the number of protons is less than that of electrons, then the atom becomes a negative ion.
Question 4.
Write short note on Cholera.
Answer:
This disease generally causes from polluted water, uncovered and fly infected food unhygienic environornent, The body is dehyadrated with bouts of vomiting. The skin becomes foggy and bluish. It is a fatal desease, so proper treatment is must for survival. Cholera is caused by a germ known as Vibrio cholerae.
Question 5.
Write short note on Malaria,
Answer:
Malaria is a mosquito carried discease. A female anopheles mosquito carries a germ called Plasmodium vivax or Phasmodium falciparum and injects it in the blood stream of a healthy person to cause malaria. High fevers with tremors are a common symptom. Headache and enlargement of splen and liver, joint pain and body ache are other symptoms. If may be fatal if not prompty treated.
Question 6.
Write short note on Dengue,
Answer:
A type of mosquito called Aedes egypti carries the germ of this disease. The germ is known as flavi virus. High fever, headache, joint pain and lowering of platelet count to a dangerous level causing obstruction and coagulation of blood are the common incidents. Oozing of the blood is the main symptom of the disease, by destroying the white blood corpuscles (WBC). Unless treated in time, dengue can be fatal.
Question 7.
Write short note on Plague.
Answer:
This disease is transmited by rats to the human body. A bacterium called Yersinia pestis is responsible for this disease. The main symptoms are lung infection, blood clothing, severe pain from swelling of the lymph gland, vomiting and oozing of blood with cough.
This disease can be transmitted by various means such as sneezing, direct body contact, touching infected soil and even from bites of flying insects. A type of fly called Xenopsylla cheopis carries the bacteria from body of rat afflicted with plague.
Question 8.
Write short note on Tuberculosis.
Answer:
Mycobacterium tuberculosis is responsible for this disease. This bacterium attacks the lungs of human beings. Tuberculosis can occur in intestine and bones. This disease is highly infectious. Infection can occur from cough and mucous an even through spits and saliva.
Symptoms of the disease are severe cough, with the letting of blood, profuse sweating and gradual loss of weight. It can be cured by DOTS or directly observed treatment, short course.
Long Questions & Answers : (3 marks for each question)
Question 1.
Explain how cloud forms and bring rain?
Answer:
The air containing water vapour rise upward. Air from surrounding region rushes toward this place and also starts to move upward. In the upper layer of the atmosphere the temperature and pressure of air is less. The water vapour rises up into the sky and condenses. As a result the vapour converts into droplets thus cloud is formed.
A time comes when the water droplets become so heavy that they come down due to gravity. Even the winds of high speed in the upper layer of the atmosphere cannot stop the downward motion of water droplet. By this time the formation of clouds for thunderstorm has completed. Then the wind also starts to go downward. In such a situation rain and storm begin on earth.
Question 2.
Explain how lightning and thunder occur.
Answer:
The lower portion of a cloud generally carries negative charges and the upper portion carries positive charges. Air of the atmosphere acts as an insulator and the charges do not flow. When a huge amount of charge builds up and when clouds with unlike charges come close to each other, the insulation of air breaks down and there is a heavy electric discharge between two cloud having opposite charges or between a charged cloud and the ground.
This causes a large amount of energy to be in the form of heat, light and sound. The flash of light is the lighting we see, and the large amount of heat causes expansion and vibration of air resulting in the thundering sound.
Question 3.
Explain how lightning causes harm and precautions we can take during lightning.
Answer:
Lightning can cause great harm. It can kill human beings and animals, destroy buildings, melt metals and also cause fires. We should take the following precautions during lightning —
Question 4.
What is a lightning conductor, how it works?
Answer:
Lightning conductor is a device that protects houses and electrical equipments within the house. A metallic rod is installed at the highest point of the building. At the highest point of the rod, there exist some small skewers. A wide metal plate is buried at least 5-6 feet deep into the ground. A thick wire of good conductor is connected to the metal plate and the rod.
This system protects the house from lighting. The high voltage of current produced in lightning is transferred to the earth through the easy route of the wire. Even if lightning strikes the house, no damage occurs to the house.
Question 5.
Define the types of epidemic
Answer:
Types of epidemic are —
Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.4 Chemical Effects of Electricity Reaction offer valuable context and analysis.
Multiple Choice Questions & Answers : (1 mark for each question)
Question 1.
Which of the following is non-eiectrolyte?
i) pure water square
ii) solution of glucose and water square
iii) liquid ammonia square
iv) all of tise above
Answer:
iv) all of the above
Question 2.
Which of the following is electrolyte?
i) soluton of sugar and water
ii) graphite
iii) water solution of H2 SO4
iv) water solution of glucose
Answer:
iii) water solution of H2 SO4
Question 3.
During zinc plating in anode is given-
i) iron item
ii) copper item
iii) graphite rod
iv) zinc rod square
Answer:
iv) zinc rod
Question 4.
During electrolysis of water gas produced in anode is-
i) oxygen
ii) hydrogen
iii) chlorine
iv) nitrogen
Answer:
i) oxygen
Question 5.
Plating of zinc is done to-
i) to increase beauty
ii) to prevent rusting
iii) none of the above
iv) both of the above
Answer:
iv) both of the above
Question 6.
Plating with zine is called-
i) Seradisation
ii) Galvanisation
iii) Oxidation
iv) Reduction is
Ans:
ii) Galvanisation
Question 7.
Metal used for coating on iron pipe-
i) zinc square
ii) silver
iii) nickel
iv) chromium
Answer:
iii) nickel
Question 8.
Electrolysis is used for-
i) metal extraction
ii) purification of metals
iii) electroplating
iv) All the above
Answer:
iv) All the above
State whether True or False : (1 mark for each question)
1. After a long use the handle of a bicycle lose their glaze.
2. To remove the impurities, the impure copper is purified by electroplating method.
3. In electrolysis insulated electrical wires are required for sonnections.
4. Substances like butter, ghee are not soluble in water.
5. The electrode sonnected with the positive end of battery is called cathode.
6. Disilled water mixed with salt is a bad conductor of electricity.
7. Examples of electrolytes are acid, alkali solution.
8. Elcctrolysis of fused NaCl produces sodium metal.
Answer:
1. true
2. false
3. true
4. true
5. false
6. false
7. true
8. true
Fill in the blanks : (1 mark for each question)
1. Conduction of electricity through a metai means movement of _______.
2. CuSO4 is a ______ electrolyte.
3. The compounds which do not prodace ions are calied _____.
4. The hope of _____ is taken to give the metallic coating on an object of another metal.
5. Rusting of iron occurs in contact with ____ and moisture of air.
6. Parts of a bicycle or a car or a bran tap are coated with ____.
7. To protect iron tools or utensils from rusting a thin coating of ____ is given on them.
8. Nickel plated substances are attracted by _______.
9. Impure copper is purified by _______ method.
10. Some electrolytes remain completely _______ in solution.
11. An LED can glow even at a low _______.
12. During electroplating the substance on which plating to be done is taken as _______.
Answer:
1. electrons
2. strong
3. non-clectrolytes
4. electrolysis
5. oxygen
6. chromium
7. nickel
8. magnet
9. electrolytic
10. dissociated
11. current
12. cathode
Match the following : (1 mark for each question)
a) Match the column A with column B.
| Column A | Column B |
| a) In elect: olysis of water get | i) are essential for our body |
| b) coating of zinc is given | ii) impure metal is taken as anode |
| c) Salt mixed water | iii) is a strong electrolyte |
| (d) NaCl | iv) is a bad conductor of electricity |
| e) Solution of water and glucose is | v) hydrogen and oxygen |
| f) At the time of electro- plating | vi) is a good conductor of electricity |
| g) Minerals present in drinking water | vii) in the process of electrolysis |
Answer:
a) In eletrolysis of water we get hydrogen and oxygen.
b) Coating of zinc is given in the process of electrolysis.
c) Salt mixed water is good conductor of electricity.
d) NaCl is a strong electrolyte.
e) Solution of water and glucose is a bad conductor of electricity.
f) At the time of electroplating impure metal is taken as anode.
g) Minerals present in drinking water are essential for our body.
Very Short Questions & Answers : (1 mark for each question)
Question 1.
Name a non-metal conductor.
Answer:
Graphite is a non-metal conductor.
Question 2.
Give an example of electrolyte.
Answer:
NaCl is an electrolyte.
Question 3.
Name a non-electrolyte.
Answer:
Sugar is a non-electrolyte.
Question 4.
Name a substance which is electrolyte even in solid state.
Answer:
Sodium.
Question 5.
To give a coatng of copper on a substance what is given as electrolyte solution?
Answer:
Water solution of copper’sulphate
Question 6.
Split (NH4)2 SO4 in ions.
Answer:
(NH4)2 SO4 = 2+
Short Questions & Answers : (2 marks for each question)
Question 1.
What are electrolytes? Give example.
Answer:
The compounds which are able to conduct electricity in a fused state or in a solution, are called electrolytes. Examples of electrolyies are acid or aikyle soluton, aqueous solution of a salt, fused NaCl etc.
Question 2.
What is electroplating?
Answer:
Electroplating is the process by which electric current is use to deposit one metal on the surface of another metal.
Question 3.
During electroplating which is taken as cathode and anode?
Answer:
During electroplating the substance on vhich plating is to be done is taken as cathode. The metal with which it is to be plated is taken as anode.
Question 4.
What is galvanized iron?
Answer:
Rusting of iron occurs in contact with oxygen and moisture of air. So another metal, zinc is coated over iron. It is called zinc-plated or galvanized iron.
Question 5.
How can you differ between stainless steel and nickel-coated iron?
Answer:
Nickel plated iron is attracted by a magnet very strongly, whereas stainless steel is not strongly attracted by a magnet.
Question 6.
Why wax, butter, ghee etc are non-clectrolytes?
Answer:
To be an electrolyte. a substance must produco ions in a fused state or in solution. None of these compounds produce ions. so these are not electrolytes.
Long Questions & Answers : (3 marks for each question)
Question 1.
Name the ions produced by potassium hydroxide, sulphuric acid and potassium nitrate in an aqueous solution.
Answer:
potassium hydroxide arrow K and OH
Sulphuric acid arrow H– and
Potassium nitrate arrow K– and
Question 2.
What is eiectrolysis?
Answer:
When chemical change of a substance occurs upon passage of electricity through a fused state or a solution, it is called electrolysis. Electrolysis is a redox reaction. Reduction occurs at cathode, the electrode connected to the negative terminal of the battery. Oxidation occurs at anode, the electrode connected to the positive terminal of the battery.
Question 3.
Why some acid or alkali is added with pure water in an experiment?
Answer:
Actually, the number of ions in pure water is so low, that it is not a good conductor of electrcity. So the number of ions in water must be increased. For this purpose some alkali ( NaOH or KOH ) or some acid (H2 SO4) is to be added to water. As they are strong electrolytes, the number of ions in the solution increases. Then it becomes possible to carry out electrolysis.
Question 4.
What are strong and weak electrolytes?
Answer:
Some electrolytes remain completely dissociated in solution. These are called strong electrolytes. e.g NaCl. KOH, H2 SO4, CuSO4 etc.
There are some electrolytes that remain ionised in solution only to a very small extent. These are called weak electrolytes. e.g acetic acid.
Question 5.
Give three important uses of electrolysis.
Answer:
i) Metal Extraction : Some metals are separated from their compounds by electrolysis. Some of these are sodium, potassium and calcium.
ii) Purification of metals: The metal primarily obstained from copper are is impure. To remove the impurities, the impure copper is purified by electrolytic method.
iii) Electroplating : Articles made of iron or steel are electroplated with nickel or chromium through electrolysis to prevent them from rusting.
Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.3 Chemical Reaction offer valuable context and analysis.
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-
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 6 The Structure of Living Organisms offer valuable context and analysis.
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 —
Or
(ii) Organelles help in synthesis, storage or secretion of different component —
(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.
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 :
Question 3.
What are the different types of plant tissues?
Answer:
Plant tissues are mainly classified as —
Question 4.
What are the different types of animal tissues
Answer:
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:
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:
Question 4.
Describe the different functions that occur in plants throughout a day.
Answer:
Question 5.
What are the functions of meristematic tissue?
Answer:
Question 6.
What are the functions of permanent tissues?
Answer:
Question 7.
Describe the functions of Epithelial tissues?
Answer:
Question 8.
What are the functions of nerve tissues?
Answer:
Question 9.
Briefly explain the functions of connective tissue?
Answer:
Question 10.
What are the functions of muscular tissues?
Answer:
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 –
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.
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:
Question 2.
Describe Dalton’s Atomic Theory.
Answer:
Dalton proposed the following postulates about the structure of matter-
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 2.1 Nature of Matter offer valuable context and analysis.
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:
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+, PO43- 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 7 World of Microbes offer valuable context and analysis.
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:
Question 2.
Write some characteristics of Bacteria.
Answer:
Question 3.
Write some characteristics of Protozoa.
Answer:
Question 4.
Write some characteristics of Fungi.
Answer:
Question 5.
Write some characteristics of Algae.
Answer:
Question 6.
Write some characteristic features of virus.
Answer:
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:
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: