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Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.1 Force and Pressure offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.1 Question Answer – Force and Pressure

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

Question 1.
A push or pull on an object is called as–
i) push-pull
ii) force
iii) pressure
iv) all of above
Answer:
ii) force

Question 2.
What is the cause of change in motion or change in the state of motion?-
i) pressure
ii) friction
iii) atmospheric pressure
iv) force
Answer:
iv) force

Question 3.
A ball rolling on the ground slows down and finally stops. It is because of –
i) force
ii) less force
iii) friction
iv) none of the above
Answer:
iii) friction

Question 4.
Pressure is defined as-
i) Area/Force on which it acts
ii) Force/Area on which it acts
iii) Volume/Force on which it acts
iv) Force/Volume on which it acts
Answer:
ii) Force/Area on which it acts

Question 5.
In a tag of war, two teams pulling a rope does not move towards any team, it implies that-
i) An equal force is being applied in the opposite direction
ii) An equal force is being applied in the same direction
iii) No force is applied in any direction
iv) Can not be explained
Answer:
i) An equal force is being applied in the opposite direction

Question 6.
When two forces, applied on an object, are equal and opposite, then the forces-
i) May move the object
ii) May stop a moving object
iii) May move the object and also cause a change
iv) Do not move the object but may cause a change in its shape
i Answer:
iv) Do not move the object but may cause a change in its shape

Question 7.
Friction produces-
i) light
ii) alpha rays
iii) heat
iv) all of the above
Answer:
iii) heat

Question 8.
A liquid exerts pressure in directions-
i) upward
ii) downward
iii) sidewards
iv) all
Answer:
iv) all

Question 9.
The air prèssure on our body is equal to-
i) Atmospheric pressure
ii) sea botton pressure
iii) space pressure
Answer:
i) Atmospheric pressure

Question 10.
The SI unit of pressure is-
i) N m³
ii) N m²
iii) kg m²
iv) pa m²
Answer:
ii) N m²

Question 11.
The standard atmospheric pressure is –
i) pressure of a mercury column of height 76 cm
ii) mercury of 10 metre
iii) pressure of 76 mm mercury column
is Answer:
i) pressure of a mercury columin of height 76 cm

Question 12.
The upward force exerted on a body by the fluid in which it is submerged is called the –
i) Immersion
ii) Buoyancy
iii) Weight
Answer:
ii) Buoyancy

Question 13.
On which of the following pressure of liquid does not depend –
i) depth of liquid
ii) upper surface area of liquid
iii) density of liquid
Answer:
ii) upper surface area of liquid

Question 14.
Density of saline water is – than purified water.
i) more
ii) less
iii) same
Answer:
i) more

Question 15.
Density of mercury is –
i) low high
iii) very high
iv) very low
Answer:
iii) very high

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

1. Presure of saline water is greater than purificd water.
2. Buoyancy is a kind of force.
3. If the weight of an object is greater than buoyancy of that object it gets immerged in water.
4. Pressure on any point of liquid is same.
5. In SI system unit of pressure is Newton/meter ²
6. Density of kersone oil is less than desnity of water.
7. Buoyancy acts towards the weight of an object.
8. The syringe works on a principle of atmospheric prussure.
9. Newton’s first law of motion is alternatively called as law of inertia,
10. Cutting and piercing tools have blunt edeges.
11. Camel can not walk on sand due to its broad feet.
12. Force of friction is greater in case of smeoth surface.
13. Fluids exert pressure.
14. When an object remains stationary on a surface, the object exerts downward force on the surface vertically
15. Pressure and force dscides the direction of flow of a liquid.
Answer:
1. true
2. false
3. true
4. false
5. true
6. true
7. false
8. true
9. true
10. false
11. false
12. false
13. true
14. true
15. fale

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

1. Force = mass of the objeet × ______.
2. SI unit of measuring forte ______.
3. When you are holling a weight of 1 kg in your hand, the force that is applied on your hand is around ______ Newton.
4. We can change the derection of a moving body by applying ______.
5. Litre is the unit of ______.
6. Frictional force works against the ______ of an object.
7. In SI system unit of density is ______.
8. Density of nercury = ______ gram/cubic centimetre.
9) Mass = Density × ______.
10. The force per unit area applied to the surface of a object is known as ______.
1Question 1. The strength of force is usually expressed by its ______.
12. Powder is sprinkled on the carom board to reduce ______.
13. Sliding friction is ______ than the static friction.
14. Friction depends upon ______ of the surface.
15. Water and other liquid exerts ______ when objects move through them.
Answer:
1. acceleration
2. Netwon
3. 9.8
4. force
5. volume
6. velocity
7. Kg m³
8. 13.6
9. volume
10. pressure
11. magnitude
12. friction
13. smaller
14. nature
15. force of friction.

Match the following : (1 mark for each question)

a) Match the column A with column B.

Column A	Column B
a) In CGS system unit of force is	i) Buoyancy
b) If density incrase presure of liquid	ii) is greater than purified water.
c) Value of acceleration due to gravity	iii) 980 cm / sec2
d) The principle of buoyancy is stated by	iv) measuring cylinder
e) Upward force exerted on a body is called	v) is called acceleration
f) Density of saline water	vi) 980 cm / sec2
g) Volume of liquid is measured by	vii) dyne
h) The rate of change of velocity with time	viii) scientist Archimedes
i) Density of water is	ix) increase

Answer:
a) In CGS system, unit of force is dyne.
b) If density increase pressure of liquied increase.
c) Value of acceleration due to the gravity 980 cm sec²
d) The principle of buoyancy is stated by scientist Archimedes.
e) Upward force exerted on a body is called buoyancy.
f) Density of saline water is greater than purified water.
g) Volume of liquid is measured by measuring cylinder,
h) The rate of change of velocity with time is called acceleration.
i) Density of water is lg cm³.

b) Match the column A with column B.

Column A	Column B
a) A liquid exerts pressure	i) law of inertia
b) Pressure decides the direction	ii) is the unit of area
c) Density of the substance	iii) to reduce friction
d) Newton’s first law of motion	iv) is less than water
e) Lubricant is used	v) of a liquid
f) Fluids	vi) exert pressure
g) Square meter	vii) in all directions
h) Density of kerosene oil	viii) mass of unit volume of any substamce

Answer:
a) A liquid exerts pressure in all directions.
b) Pressure decides the direction of a liquid.
c) Density of the substance mass of unit volume of any substamce.
d) Newton’s first law of motion law of inertia.
e) Lubricant is used to reduce friction.
f) Fluids exert pressure .
g) Square meter is the unit of area.
h) Density of kerosene oil is less than water.

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

Question 1.
What is the SI unit of force?
Answer:
Newton.

Question 2.
What is the unit of pressure?
Answer:
Pascal.

Question 3.
What is the rate of change of velocity called?
Answer:
Acceleration

Question 4.
What is unit of acceleration is CGS system?
Answer:
cm sec²

Question 5.
What is the CGS unit of pressure?
Answer:
dyne / cm².

Question 6.
What is density?
Answer:
Mass of unit volume of any substance is known as density of the substance.

Question 7.
What is the SI unit of density?
Answer:
kg m³

Question 8.
Gallon is the unit of which substance?
Answer:
A gallon is a unit of measurement of density of liquids.

Question 9.
What is pressure?
Answer:
The force per unit area applied on the surface of an object is known as pressure.

Question 10.
If same force is exerted on a substance and area increases then will the pressure increase or decrease?
Answer:
pressure will decrease.

Question 11.
Name the instrument which is used to measure liquid pressure?
Answer:
Monometer.

Question 12.
Is friction is same for sll the surfaces?
Answer:
No.

Question 13.
What is the weight of substance?
Answer:
The weight of a body is the force with which the earth attracts it.

Question 14.
Due to which acceleration a substance fall downwards?
Answer:
Acceleration due to gravity.

Question 15.
What is the SI unit of acceleration due to gravity?
Answer:
9.81 in 7 sec².

Question 16.
Force of friction is greater in case of rough surface or smooth surface?
Answer:
Rough surface.

Question 17.
Give an example to show friction produces heat.
Answer:
Rubbing of our palm produces heat.

Question 18.
Can we reduce friction to zero by using lubricants?
Answer:
No it is not possible to entirely eliminate friction.

Question 19.
Name the device used for neasuring force acting on an object.
Answer:
Spring balance.

Question 20.
Does acceleration due to gravity depend on mass?
Answer:
No.

Question 21.
When upthrust would be greater saline water or pure water?
Answer:
Saline water.

Question 22.
From, which Newton’s law we get a concept about action and recation?
Answer:
Newton’s thisd law of motion.

Question 23.
What ts the realtion between force, mass and accleration acting on an object?
Answer:
Force = mass of the object × acceleration.

Question 24.
What is the density of water in SI sytem?
Answer:
1000 kg cc.

Question 25.
Whose unit is square meter?
Answer:
Square meter is the unit of area.

Question 26.
What is acceleration?
Answer:
Acceleration is the rate of change of velocity with time.

Question 27.
What is SI unit of acceleration?
Answer:
SI unit of acceleration is m sec².

Question 28.
Why vehicles slow down when breaks are applied?
Answer:
Because of friction.

Question 29.
What is spring balance?
Answer:
Spring balance is a weighing device which is used to measuring on an object.

Question 30.
What happens when the forces ars applied on an object in the same direction?
Answer:
Forces applied on an object in the same direction add to one another.

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

Question 1.
What is force?
Answer:
A force is that physical cause which change (or tends to change) either size or shape or the state of rest or motion of the body.

Question 2.
Define friction?
Answer:
Friction is a force that resists the motion of an object that is in contact with another object or material.

Question 3.
What is frictional force?
Answer:
A force is that pliysical cause which clianges (or tends to change) eitrher size or shape or the state of rest or motion of the body, along the surface in contact. This is called the frictional force or the force or the force of frictions

Question 4.
Define static friction.
Answer:
Static friction is the friction between two or more solid objects that are not moving relative to each other. For example, static friction can prevent an object from sliding down a slopped surface:

Question 5.
Define sliding friction.
Answer:
When the object starts to move on being pulled, the frictional force which operates is known as sliding friction.

Question 6.
Write the formula of pressure per unit area in liquid.
Answer:
Pressure = depth × density of liquid × acceleration due to gravity.
∴ Pressure (p) = h d g
Where h = depth, d = density, g = gravity.

Question 7.
Same volume of water is taken in a tumbler and in a pipe-shaped vessel, which will exert more pressure?
Answer:
Pipe-shaped vessel will exert more pressure, because = depth × density of .liquid × acceicration due to gravity. Depth of pipe-shaped vessel is greater-than tumbler so it exerts more pressure than tumbler.

Question 8.
Why kerosene oil floats on water?
Answer:
Density of kersosene oil is less than water so kerosene oil floats on water. That means, mass of 1 cc of kerosene is less than same amount of water. So kerosene oil floats on water.

Question 9.
What is acceleration to gravity?
Answer:
When a body falls freely under gravity, the acceleration produced in the body due to the earth’s gravitational attraction is called the acceleration due to gravity.

Question 10.
State Pascal’s law of fluid.
Answer:
Pascal’s law states that if pressure is applied at any point on an enclosed liquid, it is transmitted equally in all direction, with undiminished force, and acts right angles to the surface of the vessel.

Question 11.
Can Pascal’s law be applied on water of a pond?
Answer:
No, Pascal’s law is not applicable on water of a pond as it not enclosed. Pascal’s law is applicable on enclosed liquid.

Question 12.
What is stądard atmosphric pressure.
Answer:
At 45° latitude the pressure exerted by a vertical column of height 76 cm is called standard atmospheric pressure.

Question 13.
With what gravitational force earth pulls towards its gravity, a 7 kg mass object?
Answer:
Gravitational pull of 7 kg mass object = 7 × 9.8 newton = 68.6 newton.

Question 14.
Will the height of mercury column be 76 cm everywhere on earth-explain.
Answer:
Atmosphheric pressure is not the same at all places. Its value is maximum at sea level and decreases as we go to higher altitudes. So the height of mercury column will not be 76 cm every where on earth.

Question 15.
Give two examples of the property of equilibrium.
Answer:
Two examples are-
i) Artesian well ii) water suppling system of city.

Question 16.
Define Buoyancy.
Answer:
When an object is immersed in a liquid, then the liquid exerts an upward force on the object. This force is known as buoyancy.

Question 17.
Give some example to support the statement that ‘friction is important for most of our day to day activities’.
Answer:
For writing with a pen or pencil, for fixing nail in the wall, for lightening of a match stick etc friction is used.

Question 18.
Why sole of shoes are grooved?
Answer:
Sole of shoes are grooved to increase friction so as to provide shoes a better grip on the floor.

Question 19.
Mention Newton’s first law of motion.
Answer:
A body at rest or uniform motion will continue to be at rest or uniform motion until and unless a net external force acts on it.’

Question 20.
‘Mention Newton’s second law of motion.
Answer:
The greater force applied on an object, the greater is the acceleration or change of velocity of the object per second.

Question 20.
Mention Newton’s third law of motion.
Answer:
When an object exerts a force on another object, the latter also exerts an equal and opposite force on the former.

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

Question 1.
Describe Archimede’s principle.
Answer:
Archimede’s principle states that if a body is partly or wholly immersed in a liquid it experiences an apparent loss in weight due to upthrust and the apparent loss is equal to the weight of the liquid displaced by the immersed part of the body.

Question 2.
How will you proof that when an object is immersed in water the object had an apparent loss of weight?
Answer:
A heavy object is hung from a spring balance. The weight of the object can be found from the recording of the spring balance. Now the object is immersed in a liquid while it hung from the spring balance. We will observe that the recording of the spring balance is lowered due to immersion of the object into the liquid. This occurs as the liquid exerts an upward force on the object.

Question 3.
What are factors that affect the upthrust?
Answer:
The upthrust due to a liquid on a body depends on the following two factors :
i) the volume of the body submerged in the liquid, and
ii) the density of the liquid, in which the body is submerged.

Question 4.
Why the walls of dams at the base are made thicker?
Answer:
We know that a liquid exerts the same pressure in all directions at a given depth. Pressure exerted by a liquid = height of liquid column × density of the liquid × acceleration due to gravity. So lateral pressure increases with the depth of liquid. On the upper portion of the dam density is less so the pressure is also less. Walls of dams at the base are made thicker in order to withstand the grater lateral pressure of water at that depth.

Question 5.
Why a piece of the thermocol flaots on water while an iron nail sinks in water?
Answer:
The piece of thermocol floats, while the iron nail sinks. The difference in behaviour of the two obviously lies in the difference in their densities. The density of thermocol is less than the

Question 6.
Define the teums thrust and pressure. What is the relation between them?
Answer:
The force acting normally on a surface is called the thrust. The thrust on unit area of the surface is called the pressure. The relation between thrust and pressure is Thrust = Pressure × Area.

Question 7.
Why ice floats on water?
Answer:
The density of ice is less than the density of water. The density of ice is 0.917³ gm and that of water is 1 g cm³ .12 cc ice melts and we get 11 cc water. When ice is submerged in water it displaces water lesser than density of water. So ice floats on water.

Question 8.
Why a piece of iron unimerges in water but floats on mercury?
Answer:
Density of iron is greater than water. So the weight of iron is greater than the buoyant force of water so iron sinks is water. Mercury has greater density than iron. So when iron is immersed in mercury weight of iron is less than the buoyant force of mercury so it floats on mercury.

Question 9.
It is easier for a man to swim in sea water than in fresh (or river) water, why?
Answer:
The reason is that due to the presence of minerals (salt etc), the density of sea water ( = 1.026 g cm³) is more than the density of fresh (or river) water ( = 1.0 g cm³). When a small portion of the body of a mark submarges in sea water, the weight of sea water displaced becomes equal to the total weight of the body. While to displace the same weight of freșh (or river)-water, a large portion of the body will have to be submerged in water. So it becomes difficult to swim in river water.

Question 10.
An iron nail sinks in while a ship-floats, why?
Answer:
If we place an iron nail on the surface of water, it sinks. This is because the density of iron is greater than of water, so the weight of the nail is more than the upthrust of water on it (or the weight of water displaced by the nail). On the other hand, ships are also made of iron, but they do not sink because the ship is hollow and the empty space in it contains_air which makes the average density of ship less than that of water. Therefore the weight of watêr displaced by the submerged part of the ship becomes equal to the total wieght of the ship and therefore the ship floats.

Question 11.
Why deep sea divers need special protective suit?
Answer:
The sea divers need special protective suit to wear because in a deep sea, the total pressure exerted on the diver’s body becomes much more than his blood pressure. To withstand it, he needs to wear a special protective suit. otherwise his body would get crushed.

Question 12.
Why there is possibility of sinking of a ship when it sails from sea water to river water?
Answer:
The density of sea water is more than the density of river water. According to the law of floatation, to balance the wieght of ship, a greater volume of water is required to be displaced. Therefore, when a ship sails from the sea of water of higher density to the river of water of lower density, possibility arises of sinking of ship.

Question 13.
Explian the property of equlilibrium of liquid.
Answer:
If water is poured in different vessels and if they are connected with each other, it will be each other, it will be observed that the level of water in each vessel will be same. This property of liquid seeking its own level is called the property of equilibrium.

Question 14.
What is Torricellian vaccum? What is there in this vacuum?
Answer:
Al m long tube is filled completely with pure and clear mercury and inverted into a through containing mercury. Some mercury from the tube flows down into the through. The mercury column now stands at a height of 76 cm above the surface of the mercury surface in the through, creating an empty space, near the closed end of the tube, this is called Torricellian vacuum. Mercury vapour fills this Torricellian vaccum.

Question 15.
What are the different types of friction?
Answer:
Friction are of two types-(i) Static Friction and (ii) Sliding friction.
i) Static Friction : When a object remains static on a surface, even through it has been pulled with a force, then the frictional force which operates is known as Static Friction.
ii) Sliding Friction : When the object starts to move on being pulled, the frictional force which operates is known as Sliding Friction.

Mathematical Problems ; (3 marks for each question)

Question 1.
Mass of an object is 5 gram and pressure of 10 dyne is exerted upon it. What amount of acclaration will be created?
Answer:
Force = mass of the object × acceleration
Acceleration = \(\frac{mass} {force} = \frac{10}{5}\) cm sec² = 2 cm sec².

Question 2.
Mass of an object is 2 kg. What would be its weight?
Answer:
Weight = Mass × Acceleration due to gravity
Acceleration due to gravity = 9.8 m sec²
∴ Weight = 2 × 9.8 newton = 19.6 newton.

Question 3.
Find out the amount of pressure at the base of a 10 m deep clear water lake. Atmospher’e pressre = 76 cm presure of mercury column and density of mercury = 13.6 gm cm³
Answer:
Pressure of base of lake = Atmospheric pressure + pressure of 10 m death water. = 76 × 13.6 × 980 + 10 × 100 × 1 × 980
= 980(76 × 13.6+10000) dyne cm²
= 980 × 2033.6 dyne cm² = 1.993 × 10⁶ dyne cm²

Question 4.
If density of mercury is 13.6 gm cm³, then find the mass of 1 lit mercury?
Answer:
Density of mercury is 13.6 gm cm³
∴ Mass of 1 cm³ mercury = 13.6 gm
Now I lit = 1000 cm³
∴ Mass of 1000 cm³ or 1 lit mercury is
1000 × 13.6 gm = 13600 gm = 13.6 kg

Question 5.
Find out the pressure of 10 cm deep water column.
Answer:
pressure of water column (p) = h d g
when h = depth = 10 cm
d = density of water = 1 g cm
g = 980 cm sec²
∴ p = 10 × 2 × 980 dyne = 9800 dyne cm²

Question 6.
Find the value of standard and atmospheric pressure or 76 cm. mercury column in SI unit.
Answer:
We know that pressure (p) = h d g here h = 76 cm
d = density of mercury = 13.6 g cm
g = acceleration due to gravity = 980 cm sec²
∴ p = 76 × 13.6 × 980 dyne cm² = 1012928 dyne cm²
Newton / m² = 10129280 Newton / m² = 1.012928 × 10⁷ pascal.

Question 7.
If water is kept instead of mercury in barometer then find out the height of water.
Answer:
Of mercury barometer, height h₁ and density d₁
then p = h₁ d₁ g (g = acceleration due to gravity)
Again of water baremeter height is h₂ and density is d₂
then p = H₂ d₂ g
∴ h₁ d₁ g = h₂ d₂ g
Now height of mercury barometer is (h₁) = 76 cm
density of mercury = 13.6 g/cc
again density of water = 1 g/cc
76 × 13.6 × g = h₂ × 1 × g
∴ h₂ = 76 × 13.6 = 1033.6 cm = 10.34 m

Question 8.
A square plate of side 10 m is place horizontally 1 m bleow the surface of water. The atmospheric pressure 1.013 × 10⁵ N m². Calculate the total thrust on the plate.
(Density of water d = 10³ kg m³ g = 9.8 m s² )
Answer:
Pressure due to 1 m cloumn of water = 1 dg
= 1 × 10³ × 9.8 = 0.098 × 10⁵ N m²
∴ Total pressure at a point lm below the surface of water = atmospheric pressure ( = Question 1.013 .× 10⁵ N M²)+ pressure due to the column of water of height 1 m.
= 1.013 × 10⁵+0.098 × 10⁵
= 1.111 × 10⁵ N m²
Area of the plate = 10 × 10 = 10² m²
∴ Total thrust on the plate = Pressure × Area = (1.111 × 10⁵) × 10²
= 1.111 × 10⁷ N.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 7 World of Microbes offer valuable context and analysis.

WBBSE Class 8 Science Chapter 7 Question Answer – World of Microbes

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

Question 1.
Microbes have survived in the earth over —
i) 5.8 billion years
ii) 2.8 billion years
iii) 8.8 billion years
iv) 3.5 billion years
Answer:
iv) 3.5 billion years

Question 2.
Microbes grow better in —
i) darker place
ii) direct sunlight
iii) water
Answer:
i) darker place.

Question 3.
A protozal disease —
i) tuberculosis
ii) hydrophobia
iii) malaria
iv) mumps
Answer:
iii) malaria

Question 4.
Microbes are of —
i) three types
ii) four types
iii) two types
iv) five types
Answer:
ii) four types

Question 5.
Vaccine of hydrophobia was discovered by —
i) Robart Koch
ii) Louis Pasteur
iii) Ehrenberg
Answer:
ii) Louis Pasteur

Question 6.
Through sneezing spreads —
i) Ringworm
ii) Malaria
iii) Allergy
iv) Tuberculosis
Answer:
iv) Tuberculosis

Question 7.
A fungal disease —
i) Ring worm
ii) Cholera
iii) Pneumonia
iv) Kaja azar
Answer:
i) Ringworm.

Question 8.
Microbes are found in —
i) water
ii) air
iii) soil
iv) everywhere
Answer:
iv) everywhere

Question 9.
If by mistake some one consumes colourful fungi, lie or she will suffer from —
i) Typhoid
ii) Polio
iii) enteric disease
iv) malaria
Answer:
iii) enteric disease

Question 10.
Baoteria, Virus P, Fungus P can convert the alcohol to vinegar.
Answer:
Bacteria.

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

1) Virus possess DNA or RNA surrounded by protein coat.
2) Tuberculosis is a water-borne disease.
3) Microbes cannot survive in direct sunlight.
4) Microbes can take food from hot foodstuff.
5) Virus is a microbe.
6) The microbes can grow better at 70° – 80°C temperature.
7) Algae can synthesise their own food.
8) Ringworm is a protozoal disease.
9) Some colourful fungi are poisonous.
10) Chlamydomonas is multicellular.
11) Dry places are ideal for growth and survival of the microbes,
2) All viruses are parasites and disease-causing agents.
Answer:
1) true
2) false
3) true
4) false
5) true
6) false
7) true
8) false
9) true
10) false
11) false
12) true

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

1) The living organisms that cannot be seen with naked eyes are called ……………
2) Microbes have survived over ……………years in the earth.
3) The total mass of microbes is …………… of the mass of all living organisms.
4) NearIy…………… of oxygen inhaled by us come into the atmosphere from the microbes.
5) Microbes cannot survive in direct ……………
6) Microbes collect their food from ………….. and ………….. organic substances.
7) The organisms that can produce their own food are ……………
8) The …………..bacteria can grow at 100°C.
9) …………… are structurally very simple and smallest among all living organisms.
10) In Bacteria ………….. is present instead of true nucleus.
11) The description of bacteria was given for the first time by ………….. in 1683.
12) The term bacteria was first used by ………….. in 1828.
13) Presently, bacteria are placed in kingdom ……………
14) Name of a colonial algae is …………..
15) From the research of ………….. we come to know the possible existence of a virus that causes small pox.
16) ………….. are acellular.
17) ………….. bacteria live in the intestine of humans for their food and shelter.
18) The interrelationship between host and microbes are called …………..
19) ………….. is prepared from sugar or starch by using yeast.
20) When a sample of warm milk at a temperature of ………….. is mixed with ………….. present in curds, vigorous growth of bacteria takes place.
Answer:
1) microbes
2) 3.5 billion
3) 60%
4) 50%
5) sunlight
6) dead, decaying
7) algae
8) thermophilic
9) bacteria
10) spiral DNA.
11) Antonyh von Leauwen hock,
12) Ehrenberg
13) Monera
14) Volvox
15) Edward Jenner
16) virus
17) E. coli
18) parasitism
19) Alcohol
20) 37°C, Lactobacillus.

Match the following : (1 mark for each question)

a) Match the column A with column B.

A	B
1) Malaria 2) Thermophilic bacteria 3) Louis Pasteur 4) Ehrenberg 5) Lactic acid 6) The term ‘virus’ means 7) Multicellur 8) Bacteria is placed in	a) grow and survive at 100°C. b) first used the term bacteria. c) mosquito-borne disease d) discovered vaccine of hydrophobia e) poison f) present in curd g) kingdom of Monera h) Spirogyra.

Answer:
1) Malaria, mosquito borne disease.
2) Thermophilic bacteria grow and survive at 100°C.
3) Louis Pasteur discovered vaccine of hydrophobia.
4) Ehrenberg first used the term bacteria.
5) Lactic acid present in curd.
6) The term virus means poison.
7) Multicelluar — Spirogyra.
8) Bacteria is placed in Kingdom of Monera.

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

Question 1.
What are microbes?
Answer:
Besides plants and animals, many other living organisms remain scattered around us which are not seen with naked eyes, these are called microbes.

Question 2.
For how many years microbes are there in the earth?
Answer:
Microbes have survived over 3.5 billion years in the earth.

Question 3.
How many microbes are there in the soil under our feet?
Answer:
Near about 10 lakhs of microbes are there in the soil under our feet.

Question 4.
How many microbes are there in 1g of soil?
Answer:
It is speculated that about 100 crore microbes are present in 1g of soil.

Question 5.
What type of place is ideal for the growth of microbes?
Answer:
Damp and swampy places are ideal for the growth of microbes.

Question 6.
Name some microbes who find shelter in other organisms?
Answer:
Microbes who find shelter in other organisms are virus, bacteria (Monera), fungi and protozoa etc.

Question 7.
Where can we find the thermophilic bacteria?
Answer:
The thermophilic bacteria are found in hot springs and hydrothermal vent.

Question 8.
What is the shape of Bacteria?
Answer:
Bacteria have various shapes — like a eamma, rod, spiral and rounded.

Question 9.
What is present in bacteria instead of true nucleus?
Answer:
Spiral DNA (nucleoid) is present instead of true nucleus.

Question 10.
Who gave description of bacteria first time?
Answer:
Anatomy von Leeuwen hock.

Question 11.
Who discovered vaccine of hydrophobia?
Answer:
Louis Pastur, a French scientist discovered vaccine of hydrophobia.

Question 12.
Who discovered two human pathogens Cholera and Tuberculosis?
Answer:
German Scientist Robert Koch.

Question 13.
Who first used the term bacteria?
Answer:
The term bacteria was first used by Ehrenberg in 1828.

Question 14.
How many cells are there in Protozoa?
Answer:
Protozoa are unicelluar.

Question 15.
Name the locomotary organs of protozoa.
Answer:
Their locomotary organs are pseundopodia, whiplash flagella or hair-like cillia.

Question 16.
What is hyphnae?
Answer:
The small filamentous part of a fungi is called hyphae.

Question 17.
When a mycelium is formed?
Answer:
The large number of hyphae together form a mycelium.

Question 18.
Where Algae are found?
Answer:
Algae are acquatic, they are found in marine and fresh water.

Question 19.
Why Algae can synthesist their own food?
Answer:
Various types of chloroplasts are present in algae so they can synthesise their own food.

Question 20.
What the term ‘Virus’ means?
Answer:
The term ‘ Virus’ is actually a Latin word which means poison.

Question 21.
Name a unicellular and a multicellular algae.
Answer:
Chlamydomones is a unicellular algae and Sprigyra is a multicellular algae.

Question 22.
Who discovered the vaccine of small pox?
Answer:
Edward Jenner.

Question 23.
Write name of three Bacterial disease.
Answer:
Tuberculosis, Whooping Cough, Cholera.

Question 24.
Write name of three virul diseases.
Answer:
Influenza, Mumps, Pox.

Question  25.
Write name of three Protozoal diseases.
Answer:
Amoebiasis, Malaria, Giardiasis.

Question 26.
Write name of three Fungal diseases.
Answer:
Ringworm, Allergy, diseases of nose throat and lung.

Question 27.
Which crops increase nitrogen in soil?
Answer:
Leguminous crops like pulses, pea etc increase nitrogen in soil.

Question 28.
Which vitamin helps to synthesise haemoglobin in RBC?
Answer:
Vitamin B₁₂.

Question 29.
Which bacteria live in the nodule of the leguminous plant?
Answer:
Symbiotic bacteria like Rhizobium live in the root nodules of the leguminous plants.

Question 30.
What is symbiosis?
Answer:
Sometimes organisms live together for sharing their nutrition, this association is known as symbiosis.

Question 31.
How majority of the plants take nitrogen?
Answer:
Majority of the plants take nitrogen in the form of NO₃ or NH₄.

Question 32.
Name some organisms which fix atmospheric nitrogen directly.
Answer:
Clostridium, Azotobacter and a few cyanobacteria fix atmospheric nitrogen directly.

Question 33.
What is ammonification?
Answer:
After the death of plants and animals, the protein components are broken down into ammonia, this process is called ammonification.

Question 34.
What is Nitrification?
Answer:
Ammonia is converted into nitrate and nitrite by nitrifying bacteria, namely Nitrosomonas orNitrobacter, this process is called Nitrification.

Question 35.
How jute fibre can be separated?
Answer:
The jute fibre can be separated easily by decomposing pectin which is present in the cell wall of jute.

Question 36.
Which bacteria is present in curd?
Answer:
Lactobacillus bacteria.

Question 37.
Who first discovered an antibiotics?
Answer:
Alexander Flemming first discovered an antibiotic in the year 1928.

Question 38.
Name some antibiotics?
Answer:
Penicillin, Streptomycin, Chloromycetin. Ampicillin etc.

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

Question 1.
What is Staining?
Answer:
Sometimes to identify microbes under microscope we use various coloured substances for their identification, these coloured substances are known as stain and the process is called Staining.

Question 2.
What are parasitism?
Answer:
Some of the microbes that enter our body through various agents finally reach inside the cell. This interrelationship between host and microbes are called parasitism.

Question 3.
What are antigens?
Answer:
When any microbe (virus, bacteria) enters our body, many harmful compounds eminateu from their whole body or body surface and mix with our body fluids, they are called antigens.

Question 4.
What are antibody?
Answer:
A type of compound gets synthesised in our body in order to destroy the antigens. The compounds are protein in nature and are referred to as antibody.

Question 5.
What is Immunity?
Answer:
The power of resistance of any organism against infection is called Immunity.

Question 6.
What are antibioties?
Answer:
Some organic compounds produced by some bacteria and fungi under the process of grotli of other bacteria or even kill them. Many life saving drugs manufactured through different processes of purification and chemical changes of these compounds, these life-saving drugs are called antibiotics.

Question 7.
What is symbiosis, define?
Answer:
Sometimes organisms live together for sharing their nutrition. In the association of nodule-forming bacteria and root of leguminous plant in the association of E.ccoli and humans, both the bacteria never harm the host both are mutually benefited. This type of association is known as symbiosis

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

Question 1.
Write four characteristics of microbes.
Answer:

• Microbes are found almost everywhere.
• Damp and swampy places are ideal for their growth and survival.
• They collect their food from dead and decaying organic substances, from different organs, tissues or cells of animals in which they take shelter. Some are able to synthesise their own food.
• Generally, the microbes can grow better at 25tvC to 38°C.

Question 2.
Write some characteristics of Bacteria.
Answer:

• Bacteria are structurally very simple and smallest among all living organisms.
• They have various shapes – like a comma, rod, spiral and rounded.
• Spiral DNA (nucleoid) is present instead of true nucleus.
• Membraneless ceil organelle like ribosome is present.

Question 3.
Write some characteristics of Protozoa.
Answer:

• Protozoa are unicellular and placed under protista having one or more nucleus.
• They are variously shaped
• They live freely as a single entity or in a colony, some live in the host body and cause disease.
• Their locomotory organs are pseudopodia, whiplash flagella or hair-like cilia.

Question 4.
Write some characteristics of Fungi.
Answer:

• Body of Fungi is not differentiated into root, stem and leaves.
• They are unicellular or multicellular filamentous.
• They have cell wall, nucleus and other organelles but are devoid of chloroplast. Hence, they cannot synthesise their food.
• Cell wall is not similar to the cell wall of higher plants.
• They can survive in water, land either in presence or in absence of sunlight.

Question 5.
Write some characteristics of Algae.
Answer:

• Body of Algae is not differentiated into root, stem and leaves.
• They are unicellular or multicellular.
• Their cell contains cell wall, nucleus, other organelles and chloropiasts, so they can synthesise their own food.
• They requere sunlight for their growth.
• All are acquatic (marine and fresh water).

Question 6.
Write some characteristic features of virus.
Answer:

• Viruses are acellular.
• They have no boundary wall, cytoplasm or nucleus instead they possess a nucleic acid (DNA or RNA) surrounded by protein coat.
• All are parasites and disease-causing agents. They behave as inert particles, only when they enter the body of the host they behave like living being.

Question 7.
What is parasitism, define?
Answer:
Some of the microbes that enter our body through various agents finally reach inside the cell. They cannot survive alone, they depend on the host, organ or cell for their food and shelter. When they grow inside the host cell, they inhibit the normal function of the cell and hamper the physiological process of the host. It may cause death of the host. This interrelationship between host and microbes are called parasitism.

Question 8.
What is saprophytism?
Answer:
Many microbes grow’ on dead animals and help in the decay of organic matter. They decompose the organic mater into simpler compounds with the help of secreted enzymes. This helps plants consume these as nutrients. Numerous bacteria and fungi secrete digestive juices on the substratum, on which they grow end obtain their food. This process is known as saprophytism.

Question 9.
Suggest five ways in which we can preserve food?
Answer:

• By keeping food products in airtight containers (Canning).
• By mixing salt with fish, meat and fruits (salting).
• Pieces of mango, lemon onion etc can be preserved by adding vinegar (Pickling)
• Food can be preserved by storing at low temperature (Refrigeration)
• Milk can be preserved by pasteurization.

Question 10.
What is vaccination or Innnunitsation? Name some diseases which can be prevented by Vaccinations.
Answer:
Dead or weak but live microbe or weakly toxic substances released from the body of microbes are administred in a human being in a definite dose.

The defence mechanism become; activated in the individual against any particular infectious disease, in advance. This process is called Vaccination or Immunisation, it has been possible to control spreading of many diseases like typhoid, Tetanus, Polio and Diphtheria by the use Vaccines.

Question 11.
Explain some ways, of treatment of waste.
Answer:

• Any untreated waste like human faeces or untie always bear some risk for human health. Some bacteria Living in less oxygenated atmospheres are able to break down these wastes to nitrate and phosphate. They reduce the chance of infection and also increase soil fertility.
• in countries like India and China, Methanogenic bacteria degrade human or animal faces, vegetable peels and produce methane gas. They act as substitutes for coal or Kerosene.
• Some algee are being used in space shuttles to clean the air.

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.

WBBSE Class 8 Science Chapter 4 Question Answer – Occurrence of Carbon and its Compounds in Nature

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:

1. Graphite is an opaque solid, grey-black in colour.
2. It is a soft and slippery material.
3. Its density is 2.2 g / cm³.
4. It remains stable at high temperatures and possesses a high melting point of 3700° C.
5. It is a good conductor of heat and electricity.

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:

1. Carbon dioxide is heavier than air. It can be poured from one jar to another like a liquid.
2. It is colourless, has a faint smell and an acidic taste.
3. It turns moist blue litmus into red. Hence, it is acidic in nature.
4. It is fairly soluble in water. Its solubility increases with pressure forms carbonic acid in water.
5. It does not support combustion and is not a combustible gas.
6. It can be solidified at -80° C. Solid carbondioxide is called dry ice.

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 7 Science Book Solutions Chapter 4 Role of Substances in Environment offer valuable context and analysis.

WBBSE Class 7 Science Chapter 4 Question Answer – Role of Substances in Environment

(Page no. 101)

Write the names of two metallic and four non-metallic elements in the blank space.
Answer:
Metallic elements Iron, Copper.
Non ntetallic elements Graphite, Hydrogen, Sulpher, Phosphorus.

Write the names of three non-metals that are more abundant in human body than in earth curst.
Answer:
(1) Oxygen, (2) Carbon, (3) Nitrogen

We can see from the table that about 97% of the total mass of human hody can be attributed to the combined mass of four elements. Can you identify them?
Answer:

1. Oxygen
2. Carbon
3. Nirtrogen
4. Hydrogen.

(Page no. 105)

mention the different parts of plants that we take as food.
Answer:

Parts of a plant body	Name of the plant
Underground root	Beat root, carrot, radish
Underground or normal stem	Potato, sweet potato.
Flower	Cauliflower, Pumkin flower.
Fruit	Mango, Apple

We take different fruits of different plants. Do they have the same taste? Share your previous experience with your friends and complete the following table :
Answer:

Name of familiar fruits	Their taste
Lemon	Sour
Ripe Mango	Sweet
Pine Apple	Sweet
Orange	Sour and Sweet
Apple	Sweet

With the help of your teacher prepare a sugar solution, salt solution and vinegar solution.Try to recognise them by taking their taste.
Answer:

Taste of the sample solution	Sample seems to be
Sweet	Sugar solution
Salty	Salt solution
Sour	Vinegar solution

(Page no. 107)

We use acids for various purposes. Do you know any such use of acid? Discuss among yourselves and write.
Answer:

Which substance	Used in which field
Juice of lemon (citric acid)	To turn milk into posset.
Muriatic acid	To clean toilets.
Vinegar	To store fish and meat.

Now notice whether any change occurs or not :
Answer:

Prepare a solution of baking soda with drinking water in a glass with the help of your teacher.

Now taste this solution along with previously prepared vinegar solution (or filtered lemon juice) and a little of lime water. Note down your observation.
Answer:

Which solution	How does it taste
Vinegar solution	Sour
Baking soda solution	Bitter and soapy feel.
Lime water	Bitter and soapy feel.

(Page no. 108)

If you know about any other uses of lime or any other base then write down after discussion with your friends.
Answer:

Name of the substance	Its use
Sodium Hydroxide	Manufacture of soap
Magnesium Hydroxide	As an antacid. [neutralizes acidity]

(Page no. 109)

Take hibiscus petal juice into seperate glasses. Add vinegar in one glass and lime water in another glass. Note down the observations.
Answer:

Vinegar is an acid. It changes the colour of hibiscus petal juice from pink to green. Again lime water is a basic substance. It changes the colour of hibiscus petal juice from pink to red. Here Hibiscus petal juice serves as an indicator.

(Page no. 111)

Take some indicators like litmus, phenolphthalein or methyl orange. Note the change in their colourwhen they are added to various solutions, Write down your observation in the following table :
Answer:

If you know about any example of such type of neutralization reaction in your daily life around your house, share it among yourselves and write it down.
Answer:

(Page no. 114)

Test the following solutions with a pH paper and see whether they have a pH equal to greater than or less than 7.
Answer:

(Page no. 117)

You need a few pieces red and blue litmus papers and some samples to identity. Then like the previous experiments, test the samples with red and blue litmus papers and fill up the following table :
Answer:

(Page no. 118)

For proper functioning of our body, the right balance of acidity and basicity must be maintained. Different fluids of our body have different extents of acidic and basic nature (pH). Can you tell anything about the nature of those fluids mentioned below?
Answer:

(Page no. 120)

Carefully observe the two pictures of the two principal sources of our food.
1. Plant source and 2. Animal source
Make a small chart about the food you generally take from these two origins.
Answer:

In how many ways we eat these foods?
Answer:
1. raw
2. roasted
3. boiled
4. eat after cooking.

(Page no. 122)

Almost 47 compounds have been reported to be present with the sea salt among which 7 compounds are important. These are –
Answer:

(Page no. 129)

How can salt be used in following cases ?
Answer:

Problem	Use of common salt
In your toothache	You must rub gum with salt
One day when you suffered suddenly from vomiting and diarrhoea	You must take a small amount of solution made from a little salt and sugar at rugular intervals
In your throat pain	You must gargfe with mild hot water mixed with salt
A leech bites in your leg	You must use salt on the biting spot to stop bleeding
Preservation of ripe tamarind	You must add salt with tamarind
If a symptom like low blood prseeure is found in someone	He must take salty food to increase blood pressure

(Page no. 129)

Discuss with your friends and prepare a list of the things you use from morning to night. Mention whether these materials some from natural, synthetic or manmade sources.
Answer:

(Page no. 131)

Sometimes sit-and-draw competitions are held in your locality or in your school. The equipments required for this purpose are shown below. Write their names and then write after discussion whether they are natural, processed or synthetics.
Answer:

(Page no. 132)

What other things can be made from these synthetic materials.
Answer:

Name of the synthetic material	Its use cups, boxes, bottles, containers, helmets, electronic goods
Plastic	pipes, rain coat, shoes, automobile and health care goods
PVC	water pipe and tank, bottles, drums, iceboxes, toys, ropes
Polyethylene	fancy bags, seatcover, shoes, cushions etc.
Rexin	Its use cups, boxes, bottles, containers, helmets, electronic goods

(Page no. 135)

Write the names of the synthetic materials used as a body soap, washing soap or for other activities mentioned below.
Answer:

Use	Materials
Bathing and washing	bathing soap
Clesning hair	shampoo
Washing and cleaning utensils	bar soap or liquid soap

(Page no. 137)

The picture of some of your familiar things below. Can you identify them. Write their uses.
Answer:

Name of the substance	Uses
a. Vaseline	mosturises body, heal minor skin scratches and burns
b. Shampoo	used to clesnse hair
c. Lipstick	used by women to cslour lips
d. Toothpaste	used to clean and maintain nealth of the teeth
e. Body spray	They make you smell ‘extra nice’.
f. Powder	makes skin smooth, used to set makeup
g. Nail polish	to colour nails
h. Tips	used by women for beautification of face

(Page no. 137)

Make a list of colourful objects, both organic and inorganic, around you and try to know about the source of their colours with the help of your teacher.
Answer:

Objects	Source of colour
Carrot	Organic
Turmeric	Organic
Petals of rose or marigold	Organic
Coloured plastic tumbler	Inorganic

Class 7 Science Chapter 4 Question Answer West Bengal Board – Role of Substances in Environment

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

Question 1.
The most abundant element found in human body is–
i) Aluminium
ii) Silicon
iii) Oxygen
iv) Carbon
Answer:
iii) Oxygen

Question 2.
The water content in human body is near about–
i) 60 %
ii) 70 %
iii) 90 %
iv) 80 %
Answer:
i) 60 %

Question 3.
If there is increased quantity of fat in a body then water content is-
i) less
ii) exceeds
iii) remain the same
Answer:
i) less

Question 4.
Next to oxygen, the most important requirement for our survival is
i) air
ii) light
iii) water
Answer:
iii) water

Question 5.
Iron is an essential component of-
i) bones
ii) red blood cells
iii) nerve
iv) skin
Answer:
ii) red blood cells

Question 6.
The major constituent of bone is a phosphate of-
i) iron
ii) sodium
iii) magnesium
iv) calcium
Answer:
iv) calcium

Question 7.
Energy required for germination of the seed comes from-
i) protein
ii) water
iii) carbohydratrates
Answer:
iii) carbohydrates

Question 8.
Breakdown of lipids in a cell gives-
i) strength
ii) energy
iii) stimulation
Answer:
ii) energy

Question 9.
The fluid secreted from the body of an ant is-
i) acid
ii) base
iii) salt
Answer:
i) acid

Question 10.
Water in nature is-
i) acidic
ii) basic
iii) neutral
Answer:
iii) neutral

Question 11.
When acids are dissolved in water, they release-
i) oxygen ions
ii) hydrogen ions
iii) nitrogen ions
Answer:
ii) hydrogen ions.

Question 12.
The ion which is present in common salt is-
i) Sodium
ii) Potassium
ii) Berium
Answer:
i) Sodium

Question 13.
Iodine deficiency cause-
i) high blood pressure
ii) low blood pressure
iii) goitre
iv) heart disease
Answer:
iii) goitre

Question 14.
A polymer called polythene is prepared by joining molecules of-
i) Methane
ii) Chlorine
iii) Ethylene (C₂ H₄)
Answer:
iii) Ethylene (C₂ H₄).

Question 15.
The acid present in tamarind-
i) malic acid
ii) lactic acid
iii) acetic acid
iv) tartaric acid
Answer:
iv) tartaric acid

Question 16.
In general taste of alkali is-
i) acidic
ii) bitter
iii) basic
iv) tasteless
Answer:
ii) bitter

Question 17.
A crystaline subject-
i) chalk
ii) lime
iii) sand
iv) sugar
Answer:
iv) sugar

Question 18.
If the pressure of blood increases what may happen in our body-
i) veins can rupture
ii) heart valves may be damaged
iii) blood clots may be formed in the brain
iv) all are true
Answer:
iv) all are true

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

1. Most of the things of the earth are made from a reserve of about ________ elements.
Answer:
92.

2. Human body is mainiy formed of the combined mass of __________ elements.
Answer:
four.

3. We get _______ from inorganic compounds.
Answer:
minerals.

4. Using the energy of _____, plants produce glucose.
Answer:
Sunlight.

5. – is an important constituent of the body of organisms.
Answer:
Water.

6. Water constitutes about _____ of the total mass of human body.
Ans:
60 %.

7. An increased quantity of _____ correlates with a decreased _____ content.
Answer:
fat, water.

8. Next to oxygen, ______ is the most important requirement for our survival.
Answer:
water.

9. The major constituent of bone is a phosphate of ______.
Answer:
calcium.

10. Without ferrous ion (Fe²⁺) ________ of blood’s red blood cell cannot function.
Answer:
haemoglobin.

11. Energy required for germination of the seed comes from ______ stored in it.
Answer:
carbohydrates.

12. The protein called haemoglobin transports _______ to different parts of our body.
Answer:
oxygen

13. Bases soluble in water are known as _______
Answer:
alkalis

14. All _______ are bases but all bases are not alkalis.
Answer:
alkalis

15. Lemon juice causes stain on _______ floor.
Answer:
cement

16. The concentrated alkali solution is extremely harmful for skin and _______.
Answer:
eyes

17. _______ is mixed with pond water to decrease its ______ during culture of fish in pond.
Answer:
Lime, acidity.

18. Our body also contains acid in the ______.
Answer:
stomach.

19. ______ of Calcium in our body is in our bones.
Answer:
99 %.

20. _______ is necessary for deposition of Calcium in the bones.
Answer:
Vitamin D.

21. One important constituent of our blood is _______.
Answer:
White Blood Corpuscles (WBC).

22. To meet the demand of salt in reserve forests there are ______ for animals.
Answer:
salt licks.

23. ______ helps in maturation of brain, so it is essential for children.
Answer:
lodine.

24. Generally iodine deficiency problems are more in _______ regions than in plains.
Answer:
hilly.

25. The fibres in the plant body are made of different types of _______ polymers.
Answer:
carbohydrate.

26. The muscles, tendons, ligaments etc of animal bodies are made up of _______, which also are polymers.
Answer:
Proteins.

27. _______ is the sodium or potassium salt of some organic acids which are prepared from the reaction of coustic soda or caustic potash with _______ or oils.
Answer:
Soap, fat.

28. The ______ used for writing or printing is mixture of pigments.
Answer:
ink.

29. _______ is a mixture of oxides and Silicate compounds of many metals like Calcium, Aluminium, Iron etc.
Answer:
Cement.

30. Some of the widely consumed soft drinks in our country are found to contain ______ in alarming quantities.
Answer:
pesticides

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

1. Carbonic acid is present in vinigar.
Answer:
false

2. Apple contains malic acid.
Answer:
true

3. Lactic acid is present in curd.
Answer:
true

4. Our body contais acid in the stomach.
Answer:
true

5. Alkali turns moict red litmus white.
Answer:
false

6. The taste of blood is sour.
Answer:
false

7. Water does not change the colour of litmus paper.
Answer:
true

8. If our kidneys get affected due to some reason, then urea, uric acid and creatinine levels in the blood decrease.
Answer:
false

9. Common salt is a white, crystalline mixture.
Answer:
true

10. Some salt enters our body through the water we drink.
Answer:
true

11. Pure sodium chloride absorbs water from air.
Answer:
false

12. The main constituent of human blood is water.
Answer:
true

13. Milk, curd, bones of small fishes sre the main sources of iron.
Answer:
false

14. Cactas, Acacia, Palm grow in hot and dry areas.
Answer:
true

15. Iodine helps in maturation of brain.
Answer:
true

16. Many small molecules join together to form a molecule of a polymer.
Answer:
true

Match the column A with column B.

Column A	Column B
a) PET is used for	i) are present in tomato
b) Many countries has banned	ii) grow in mangrove forest
c) The substances decomposed through	iii) preparing bottle and food boxes
d) Malic, oxalic and sitric acids	iv) high temperature
c) Carbonic acid is present	v) haemoglobin cannot be formed
f) Animals that hunt at night	vi) DDT as pesticide
g) Cactus can tolerate	vii) natural process are known biodegradables
h) Without ferrous ion	viii) red litmus blue
i) Sundari trees	ix) can see in the dark
j) Alkali turns	x) in sodawater

Answer:
a) PET is used for preparing bottle and food boxes.
b) Many countries has banned DDT as pesticide.
c) The substances decomposed through natural process are known biodegradables.
d) Malic, oxalic and citric acids are present in tomato.
e) Carbonic acid is present in sodawater.
f) Animals that hunt at night can see in the dark.
g) Cactus can tolerate high temperature.
h) Without ferrous ion haemoglobin cannot be formed.
i) Sundari trees grow in mangrove forest.
j) Alkali turns red litmus blue.

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

Question 1.
What are the main constituents of common salt?
Answer:
Sodium Chloride, Magnesium Chloride, Calcium Sulphate and Potassium Bromide.

Question 2.
What is the symbol of Sodium Chloride?
Answer:
NaCl arrow Sodium ion (Na⁺) + Chloride ion (Cl-).

Question 3.
What are the two functions of Calcium?
Answer:
a) Helps in formation of bones and teeth. b) Controls the function of heart muscle.

Question 4.
What are four elements prevalent in human, bacterial, fungal, plant and animal bodies?
Answer:
Carbon (C). Hydrogen (H), Oxygen (O) and Nitrogen (N).

Question 5.
How plant produce glucose?
Answer:
Utilising carbon dioxide from air, taking up water and some minerals from soil and using the energy of sunlight, plants produce glucose.

Question 6.
How the harmful compounds of our body are excreted?
Answer:
It occurs through sweat and urine most of which is water.

Question 7.
What are the two different components of paints?
Answer:
i) Solvent part (generally colourless or light-coloured liquids)
ii) pigment part (particles of coloured compounds)

Question 8.
What is the reason for wide use of cement?
Answer:
This is because cement is easily available, can adapt itself with weather and structures made of cement have a high longevity.

Question 9.
What will happen of you prepare ball of cement, sand and water and keep it overnight?
Answer:
The entire ball will get hardened.

Question 10.
Write the name of theree non-metallic element.
Answer:
i) Oxygen ii) Carbon iii) Hydrogen

Question 11.
What link a fuel to our body?
Answer:
Regarding production of energy in the body of an organism, carbohydrates may be likened to a fuel.

Question 12.
What is protein?
Answer:
Protein is a class of compound without which life cannot be imagined.

Question 13.
Where protein is found in our body?
Answer:
Proteins are found in skin, muscle, nail, hair and blood.

Question 14.
What speed up numerous chemical reactions that occur in our body?
Answer:
Various enzymes.

Question 15.
On what the external appearance of the progeny of an organism depends. is
Answer:
The external appearence of the progeny of an organism depends on their nuclic acid.

Question 16.
What partly determines the behavioural pattern of an animal?
Answer:
The behavioural pattern of an animal is determined partly by its genetic make up.

Question 17.
Name the four metals that are essential for our survival.
Answer:
These metals are Sodium, Potassium, Catcium and Iron.

Question 18.
When you eat fried fish, you ingest very small pieces of bone along with the fish, what it contains?
Answer:
It contains a phosphate compound of Calcium.

Question 19.
What is there in the Calcium tablets prescribed by doctor?
Answer:
It contain Calcium Carbonate (CaCO₃), along with some organic substances.

Question 20.
What is there in anima! liver?
Answer:
It contains specific organic compounds of iron.

Question 21.
What is required for the proper functioning of nervous system?
Answer:
It requires the right balance of Sodium and Potassium ions (Na⁺.and .K⁺)in our body.

Question 22.
Name four organic compounds which play a vital role when life first came into being?
Answer:
i) (‘arbohydratc. ii) Protein, iii) lipid, iv) nucleic acid.

Question 23.
With what tie iatu exiernal shell of snails, conches and the like is made of?
Answer:
Calcium Carbonate.

Question 24.
How many elements are present in living organisms in form of various compounds?
Answer:
16 elements.

Question 25.
How is lipid important?
Answer:
Breakdown of lipids in a cell given energy. Moreover the layer of lipid below the skin of an animal protects it from cold.

Question 26.
Name some substances other than fruit which tastes sour?
Answer:
Sour milk, vinegar, curd.

Question 27.
What is acid?
Answer:
An acid is a substance which produces hydrogen ions (H^–)when dissolved in water.

Question 28.
From where the word acid come from?
Answer:
The word acid came from the Latin word Acidus, which means ‘sour’.

Question 29.
Name an acid which produced in our stomach, how is it useful?
Answer:
Hydrochlcric acid, it helps in the digestion process.

Question 30.
What we take to reduce acidity in stomach?
Answer:
An antacid, which is a base, is taken.

Question 31.
What is neutralisation reaction?
Answer:
The reaction of an acid with a base to form salt and water is called neutralisation reaction.

Question 32.
Which acid is present in ant bite?
Answer:
Formic acid ( HCOOH).

Question 33.
What is base?
Answer:
A base is a ompound that produces hydroxyl ions when dissolved in water.

Question 34.
What is alkali?
Answer:
A base that is soluble in water is called an alkali.

Question 35.
Write the dissociation reaction of HCl in aqueous solution?
Answer:
HCl + H₂O → H₃ ^– + Cl

Question 36.
How can you write the dissociation of slaked lime in lime water?
Answer:
Ca(OH)₂ arrow Ca⁺² + 2 OH^–

Question 37.
What is p H scale?
Answer:
The strength of acidity or basicity of a solution is measured by pH scale.

Question 38.
How much of our daily food should be acidic and basic?
Answer:
Our daily food should be 20% acidic and 80% basic.

Question 39.
Name the foods which are basic in nature.
Answer:
Foods coming from plant origin are mainly basic in nature e.g. fruits, nuts, legumes and vegetables.

Question 40.
Name the foods which are acidic in nature.
Answer:
Foods coming from animal origin like fish, meat,egg are acidic.

Question 41.
How many types of salt do we use now a days as food?
Answer:
They are mainly of three types –
(i) Sea salt
(ii) Rock salt
(iii) Table satt.

Question 42.
What is the medium of communication in our body?
Answer:
It is our nervous system, which is continuous from our nails of feet to head.

Question 43.
What assists the nerve in the activity of communication?
Answer:
To exchange impulse between brain, spine and different parts of the body the main helper of nerve is the sodium ion (Na⁺)present in the colımon salt.

Question 44.
What will happen if the level of salt in our body suddenly decreases due to some reason?
Answer:
For this sparm will occur in different parts of the body, talking will become inconsistent.

Question 45.
Where from the word ‘polymer’ is derived?
Answer:
The word ‘polymer’ is derived from two Greek words ‘poly’ and ‘meros’. ‘Poly’ means many and ‘meros’ means parts.

Question 46.
Name some fertilisers.
Answer:
Urea, Ammonium Sulphate, Ammonium Phosphate.

Question 47.
Name some pesticides.
Answer:
Methyl parathion, Aldrin, Carboryl.

Question 48.
What are the adverse effects of Lead and Mercury?
Answer:
Lead causes – loss of appetite. nausea, headache.
Mercury causes – Loss of sense in facial and tongue muscles, kidney damage.

Question 49.
What has been found in some of the widely consumed soft drinks in our country?
Answer:
Some of the widely consumed soft drinks in our country contains pesticides in alarming quantities.

Question 50.
What herbal medicine was used earlier for small cuts or bruises?
Answer:
Extract of marigold plant or grass .

Question 51.
In early days what was used for dying of clothes?
Answer:
Indigo.

Question 52.
Whose body contains more water male or female?
Answer:
male

Question 53.
Whose body contains more water child or adult?
Answer:
child.

Question 54.
Whose body contains more water a thin person or a fat man?
Answer:
thin person.

Question 55.
Whirh acid is present in vinigar?
Answer:
Acetic acid.

Question 56.
Which acid is present in orange?
Answer:
Citric acid and ascorbic acid.

Question 57.
Which acid is present in lemon?
Answer:
Citric acid and ascorbic acid.

Question 58.
Where the maximum amount of Calcium lies in our body?
Answer:
99% of Calcium in our body is in our bones.

Question 59.
What is organic Sea-salt?
Answer:
A special type of salt is produced from pollution-free ocean source, known as organic Sea-salt.

Question 60.
What is the effect of reduced activity of thyroid glands on females?
Answer:
The reduced activity of thyroid gland: may lead to infertility in females.

Question 61.
Which acid is present in apple?
Answer:
Malic acid.

Question 62.
Which acid is present in tomato?
Answer:
Malic acid, oxalic acid and citric acid.

Question 63.
Which acid is present in sodawater?
Answer:
Carbonic acid.

Question 64.
Which acid is present in tamarind?
Answer:
Tartaric acid.

Question 65.
Which acid is present in curd?
Answer:
Lactic acid.

Question 66.
What is the role of vitamin D in our body?
Answer:
Regulates the absorption of calcium and phosphorous in the intestine, mineral deposition in bones and teeth.

Question 67.
What are the function of different enzymes present in our body?
Answer:
To initiate and speed up the bio-chemical reaction.

Question 68.
How does glucose produce energy in our body?
Answer:
Glucose is broken down by enzymes during digestion to produce energy in our body.

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

Question 1.
Why is iodized salt necessary for our body?
Answer:
lodine helps in maturation of brain, so it is essential for children. Moreover, deficieicy of iodine may lead to physical and mental depression and Goitre.

Question 2.
What is pH scale? How is it important?
Answer:
The strength of acidity or basicity of a solution is measured by pH scale.
At 25° C the pH of a neutral solution (e.g. water) is 7 . The solution having a pH less than 7 (upto zero) is acidic in nature. The solution having a pH greater than 7 (upto 14) is basic or alkaline.

Question 3.
What is thyroid gland?
Answer:
If you touch the sides of your vocal chord with fingers, you will find the presence of two small glands. These are thyroid glands.

Question 4.
What is Goitre?
Answer:
In case of iodine deficiency the thyroid glands get enlarged in trying to function normally. The throat get abnormallly swollen and this is known as Goitre.

Question 5.
What is soap?
Answer:
Soap is the Sodium or Potassium salt of some organic acids which are prepared from the reactions of Caustic Soda or Caustic Potash with fat or oils.
Fats or Oils + Caustic alkali → Soap + glycerine.

Question 6.
What is polymer?
Answer:
A polymer is a chemical compound with large molecules made of many smaller molecules of the same kind. Some polymers exist naturaly and other are produced in laboratories and factories.

Question 7.
What harm nylon net are causing in the environment?
Answer:
Offsprings of Hilsa fishes and baby turtles are dying in the nylon net with smaller gaps. Thus the biodiversities are being destroyed.

Question 8.
Why centent and sand-based construction need watering?
Answer:
In prisence of water the Calcium hyroxide water also adds to different silicate compounds of cement. As heat is liberated in these reactions, cement may be cracked. So concrete casting needs watering.

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

Question 1.
How is water helpful in human body?
Answer:
Water is the most important requirement for our survival. After several days without water lruman beings may die. Water helps us to transport the simple compounds generated by digestion of carbohydrates. lipids and proteins to different parts of our body. Harmful compounds formed in our body are excreted through urine, that is basically a watery fluid.

Question 2.
What are the two factors on which the acid-base balance of human body depends? Why it is necessary to maintain a fixed acid-base balance in human body?
Answer:
The acid-base balance of human body depends mainly on two factors –
a) Amount of carbon dioxide released by respirartion.
b) Different changes by chemical reactions occuring in our body.
It is necessary to maintain a fixed acid-base balance in human body because different parts of the body enamel of teeth. bone joint are affected and aging process may become faster.

Question 3.
What is the sources of Calcium that is essential for body?
Answer:
Food from animal origin e.g. – milk, curd, bones of small fishes etc.

Question 4.
Which organization established factories of iodized salt in different parts of the country? In which year the production of iodized salt became sufficient?
Answer:
Factories for the production of iodized salt in different parts of the country were established under the collaboration of WHO and UNICEF. In 1983 the production of iodized salt became sufficient for Indian population.

Question 5.
In most cases, mango or other fruit or vegetable slices are coated with common salt and dried in the sun, why?
Answer:
This is done due to two reasons.
(i) So that mango slices lose most of the water.
(ii) So that those pickles are protected from aerial germs for a long time.

Question 6.
Why salt is used to preserve food since antiquity?
Answer:
The germs when come in contact with sait, they lose cell fluid by osmosis. As a result the germs are killed, this helps topreserve food.

Question 7.
Give example of some natural polymer.
Answer:
The fibres in the plant body are madc up of different types of carbohydrate polymers. On the other hand, the muscles, tendons, ligaments etc of animal bodies are made up of proteins. which also are polymers.

Question 8.
How many types of plastics are there?
Answer:
Plastics can be classified into two types –
i) Thermo plastics : This type of plastic is soft and can be melted and remoulded repeatedly. Examples include polyethylene, polystarene and PVC.
ii) Thermosetting plastic: This type of plastic is hard and they can be melted and moulded only once. They cannot be melted and remoulded again. Examples include bakelite, melamine, teflon.

Question 9.
What are detergents?
Answer:
Detergents are water soluble compund of organic acids prepared by the reaction of hydrocarbon compounds from petroleum or other sources, and concentrated Sulphuric acid.The commercially available detergents are mixture of different compounds.

Question 10.
What are the harmful effects of DDT and other pesticides?
Answer:
It has been found that a breakdown product of DDT makes the eggshell of birds and tortoises thin and brittle. The egg breaks into pieces as the birds sit on them during into incubation. The pesticides have adverse effects on honeybees. silkworm and different types of birds. When consume with food, the pesticide also create different types of discases in human body.

Question 11.
What does glass consists of? What mixed compound is used to prepare yellow, blue and greeen coloured glass?
Answer:
Glass is a mixture that is prepared mainly from limestone, soda ash and sand.
Metallic oxides used to prepare coloured glasses are – Iron oxide is used for yellow glass, Cobalt oxide used for blue glass and Chromium oxide is used for green glass.

Question 12.
Define biodegradable and non-biodegradable wastes.
Answer:
The subtances that degrade or decompose through natural processes are known as biodegradable. Those that are not degraded like that are known as non-biodegradable.

The two types of wastes are – Entirely different in their structures and properties like water retaining ability etc. Animal bodies are completely biodegradable but manmade synthetic products are mostly non-biodegradable.

Question 13.
What are the general properties of common salt?
Answer:

1. The colour of edible (common) salt is generally white.
2. In-normal condition it is a hard substanee.
3. Common salt is soluble in water.
4. It is a crystalline solid.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 1.4 Light offer valuable context and analysis.

WBBSE Class 8 Science Chapter 1.4 Question Answer – Light

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

Question 1.
Reflection of an object occurs due to-
i) refraction
ii) regular reflection
iii) irregular reflection
iv) all of above
Answer:
ii) regular reflection

Question 2.
If ray of light reflects perpendicular on a mirror incident angle becomes
i) 90°
ii) 0°
iii) 180°
iv) 80°
Answer:
i) 90°

Question 3.
If ray of light falls on a mirror at 30^\theta angle the reflected angle becomes-
i) 30°
ii) 90°
iii) 0°
iv) 60°
Answer:
iv) 60°

Question 4.
Virtual image –
i) ean be seen by eyes and reflected on screen ,
ii) can not be seen and can not be reflected on screen
iii) can be seen but can not be reflected on screen
Answer:
iii) can be seen but can not be reflected on screen

Question 5.
Shape of reflection created on plane mirror-
i) is of smaller size than the actual object
ii) is of larger size than the actual object
iii) is same as the object
Answer:
iii) is same as the object

Question 6.
If incident ray and reflected ray falls perpendicular on each other then refelected angle becomes-
i) 90°
ii) 45°
iii) 60°
iv) 180°
Answer:
ii) 45°

Question 7.
White light is mixer of how many colours-
i) 7
ii) 2
iii) 4
iv) 10
Answer:
i) 7

Question 8.
Which of the following series does not have lateral inversion-
i) A, B, C
ii) M, N, O
iii) X, A, O
Answer:
iii) X, A, O

Question 9.
If two plane mirrors are placed at a right angle then reflection number of that object weuld be-
i) 2
ii) 3
iii) 4
iv) 5
Answer:
ii) 3

Question 10.
What are the two marginal colours of a spectrum?
i) red and violet
ii) red and blue
iii) violet and blue
Answer:
i) red and violet

Question 11.
Spectrum occurs due to-
i) reflection
ii) refraction
iii) dispersion
Answer:
iii) dispersion

Question 12.
Distance between an object and mirror is 15 cm. If the object is brought 2 cm nearer the mirror then what will be distance between reflection and object-
i) 13 cm
ii) 4 cm
iii) 26 cm
iv) 36 cm
Answer:
i) 13 cm

Question 13.
We can see sun before sunrise and after sunset in atmosphere because-
i) refraction occurs
ii) reflection occurs
iii) dispersion occurs
Answer:
i) refraction occurs

Question 14.
In internal full reflection-
i) incident angle > reflected angle
ii) incident angle < reflected angle
iii) incident angle = reflected angle
Answer:
iii) incident angle = reflected angle

Question 15.
The optical illusion in desert is called-
i) mirage
ii) halucination
iii) imagination
Answer:
i) mirage

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

1) A real source of light is sun.
2) Virtual image can be seen by eyes and reflected on screen.
3) Refrective index of diamond with respect to air is very low.
4) The image formed in a mirror is a virtual image.
5) Periscopes are used in submarine.
6) Mirrage formed in a desert can be obtained on screen.
7) In total internal reflection the image is much brighter.
8) Shape of reflaction created on plane mirror is of smaller size than the actual size .
9) Spectrum occurs due to dispersion.
10) If the ray of light falls on a mirror at 30° angle the reflected angle becomes 90⁶.
11) Convex lens is used in magnifying glass.
12) An unreal source of light is moon.
13) Two marginal colours of the spectrum are red and blue,
14) The angle of refraction becomes greater than the angle of incidence.
15) Critical angle of diamond with respect to air is very high.
Answer:
1) true
2) false
3) false
4) true
5) true
6) false
7) true
8) false
9) true
10) false
11) true
12) true
13) false
14) true
15) fale

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

1. In reflection angle of incidence and angle of reflection is always ______.
2. Irregular reflection follows the two rules of ______.
3. ______ reflection does not form any image.
4. Plane mirror forms ______ image.
5. On a screen of cinema _______ images are formed.
6. An object is 15 cm away from mirror. The reflection formed will be _____ distant from mirror:
7. If an object is kept between two parallel mirrors ______ images are formet’.
8. If an object is kept between two mirrors which are inclined at right angle _______ images are fomed.
9. To form image on cinema screen ______ is used.
10. Virtual inage formed by convex lens is always ______ in respect of the object.
11. ______ object does not have any hateral invesion.
12. In splitting of white light, ______ light deviates the least.
13. Prism does not create any _______, only separates the band of colours present in white light.
14. A _____ is formed by the dispersion of sunlight by tiny drops of water present in the air:
15. To create virtual image by convex lens the object should be kept _____ the focus length.
16. Convex lens is used in ____.
17. Dispersion of white light is done by _______.
18. When a ray of light travels from denser medium to a rerer medium, the angle of regration is _____ than the angle of incidence.
19. When a ray of light strikes at the surface of seperation of the two media at right angle, the angle If refraction is ______.
20. Velocity of light in water _______.
Answer:
1) same
2) reflection
3) irregular
4) virtual
5) numerous
6) 15 cm
7) numerous
8) three
9) convex
10) inverted
11) Symmetrical
12) red
13) colour
14) rainbow
15) outside
16) magnifying glass
17) prism
18) more
19) zero
20) 3 × 10⁸ m / s.

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

Qustion 1.
What is light?
Answer:
Light is a kind of energy, which after rearhing our eyes creates a sensation to view things.

Qustion 2.
How much time it takes light to reach from sun to earth?
Answer:
It takes 8.3 minutes to reach light from sun to earth.

Qustion 3.
Name a real and unreal source of light.
Answer:
A real source of light is sun and an unreal source of light is moon.

Qustion 4.
Name an instrument which is made using the principal of reflection of light.
Answer:
By using the principal of reflection of light periscope instrument is made.

Qustion 5.
In a plane mirror if a ray of light reflects at 35° angle then what will be the value of reflected angle?
Answer:
The value of reflected angle would be 35°.

Qustion 6.
If a ray of light strikes a mirror perpendicularly what will be the value of reflected angle?
Answer:
The value of reflected angle would be 0°.

Qustion 7.
Which property of light is proved in a pin-bole camera?
Answer:
The property that light travels in a straight line is proved in a pin-hole camera.

Qustion 8.
In what kind of surface regular reflection occurs?
Answer:
Regular reflection occurs in smooth and polished surface.

Qustion 9.
In what kind of surface irregular reflection occurs?
Answer:
Irregular reflection occurs in rough surface.

Qustion 10.
What will be the critical angle of diamond with respect to air?
Answer:
The critical angle of diamond with respect to air is 24.5°.

Qustion 11.
In internal reflection light reflects from which medium to which medium?
Answer:
In internal reflection light reflects from denser medium to rarer medium.

Qustion 12.
Name a natural phenomena which is created due to internal reflection?
Answer:
‘Mirage’ is a natural phenomena which is created due to internal reflection.

Qustion 13.
What is absolute refractive index?
Answer:
The absolute refractive index of a medium is difined as the ratio of the speed of light in vacuum (or air) to the speed of light in that medium.

Qustion 14.
Is Mirage a virtual reflection or a real reflection?
Answer:
Mirage is a virtual reflection.

Qustion 15.
When light enters a denser medium from a rarer medium how it changes its direction?
Answer:
Light moves to wards the normal.

Qustion 16.
When light enters a rarer medium from a denser medium how it changes its direction?
Answer:
Light moves aways from the normal.

Qustion 17.
What type of image is created in a plane mirror?
Answer:
Virtual image is created in a plane mirror.

Qustion 18.
What type of reflection occurs on the page of a book?
Answer:
Irregular reflection occurs on a page of a book.

Qustion 19.
In what kind of reflection image is formed?
Answer:
In regular reflection image is formed.

Qustion 20.
What type of reflection can not be taken on a screen?
Answer:
Virtual reflection can not be taken on a screen.

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

Qustion 1.
What are the essential conditions for the total internal reflection?
Answer:
There are two necessary conditions for the total internal reflection :
i) The light must travel from a denser to a rarer medium.
ii) The angle of incidence must be greater than the critical angle for the pair of media.

Qustion 2.
What is meant when it is said that the critical angle of water with respect to air is 49° ?
Answer:
The critical angle of water with respect to air is 49° then value of refracted angle would be 90° or one right angle.

Qustion 3.
What is meant when it is said that the critical angle of diamond with respect to air is 24.4° ?
Answer:
The critical angle of diamond with respect to air is 24.4° means when ray of light travels from diamond to air then if value of incident angle is 24.4° then value of refracted angle would be 90° or one right angle.

Qustion 4.
What is critical angle?
Answer:
Critical angle is the angle of incidence in the denser medium corresponding to which the angle of refraction in the rarer medium is 90°.

Qustion 5.
On what factors the value of critical angle depends?
Answer:
The value of critical angle depends on two following factors:-
i) nature of the two media that means the refractive index of the media
ii) the colour of light.

Qustion 6.
What is the refraction of light?
Answer:
The change in direction of the path of light, when it passes from one transparent medium to another transparent medium, is called refraction. The refraction of light is essentially a surface phenomenon.

Qustion 7.
What is real image?
Answer:
The images that can be cast on screen are said to be real image. Rays of light coming from a certain point after reflection or refraction if meet at a point, then the second point is known as the real image of the first one.

Qustion 8.
What is virtual image?
Answer:
The images that can not be cast on screen are virtual images. Rays of light coming from a certain point after reflection or refraction if it seems to come from another point, then the second point is said to be the virtual image of the first point.

Qustion 9.
Write down the laws of reflection.
Answer:
i) The angle of incidence is equal to the angle of reflection.
ii) The incident ray, the reflected ray and the normal at the point of incidence. lie in the same plane.

Qustion 10.
Write down the laws of refraction.
Answer:
i) The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.
ii) For refraction of an obliquely ray of incidence of light of any given colour in a given pair of optical media irrespective of the magnitude of angle of incidence and angle of refraction, the refractive index is a constant.

Qustion 11.
What is total internal reflection of light?
Answer:
When a ray of light travels obliquely from a denser medium to a rarer medium, if the angle of incidence becomes greater than the critical angle of the media, the ray of light returns to the first media getting reflected to the surface of separation of the two media. The incident is known as total internal reflection of light.

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

Qustion 1.
Write the properties of real image?
Answer:
i) Real image is inverted with respect to the object.
ii) A photograph of a real image can be taken.

Qustion 2.
Write the properties of virtual image.
Answer:

1. A virtual image is seen with eyes but can not be obtained on a screen.
2. A virtual image is erect with respect to the object.
3. Virtual image formed on a plane mirror had lateral inversion.

Qustion 3.
Why do water on an aurum leaf appear glittering?
Answer:
From air light enters into the drop of water that moves on the aurum leaf. When rays of light try to come out again in air, it appears on the surface of separation of water and air with angle of incidence, more than the critical angle of the two media. As a result, total internal reflection takes place there. The emergent rays then reach the viewer’s eyes and the viewer finds the area glittering.

Qustion 4.
Why does diar ond look shiny?
Answer:
Refractive index of diamond with respect to air is very high. So, eritical angle of diamond with respect to air is very low only 24.5°. Diamond is cut in such a way that when a ray of light attempts to emerge for diamond, the angle of incidence exceeds the magnitude of eritical angle of diamond in air. As a result, total internal reflection occurs and diamond look shiny.

Qustion 5.
Why stars twinkle?
Answer:
Stars are very far away from earth. So the light which emits from star passes through different layers of air. Continuous change in density and refractive index of the air take place due to continuous change of temperature. As a result, the direction of light changes every moment while passing through the succesive air layers. As a result the star seems twinkling to the eye of viewer.

Qustion 6.
Distinguish between real image and virtual image.
Answer:

Real image	Virtual image
1) A real image is formed due to actual intersection of the reflected rays.	1) A virtual image is formed when the reflected rays meet if they are produced back wards.
2) A real image can be obtained on a screen.	2) A virtual image can not be obtained on a screen.
3) A real image is inverted with respect to the object.	3) A virtual image is erect with respect to the object.

Qustion 7.
Which of the following reflections are real image or virtual image, Give reasons.
i) Image on cinema screen,
ii) Image formed on still water of pond.
iii) Image formed on photography plate.
iv) Image formed by concave lens.
Answer:
i) Image on cinema screen is real image as it is obtained on screen.
ii) Image formed on still water of pond is virtual as it cannot be obtained on screen.
iii) Image formed on photographic plate is real as it can be seen as photograph.
iv) Image formed by concave lens is virtual as it cannot be obtained on screen.

Qustion 8.
Distinguish between the total internal reflection and reflection from a plane mirror.
Answer:

Total internal reflection	Reflection from a plane mirror
1) It takes place only when light passes from a denser medium to a rearer medium at an angle of incidence greater then the critical angle for that pair of media.	1) It takes place when light is incident on a plane mirror from any medium at any angle of medium.
2)The entirfe light is reflected.	2) Only a part of light is reflected while rest is refracted and absorbed.
3) There is no loss of energy. The energy of reflected ray is same as that of incident ray.	3) There is a loss of energy. The energy of reflected ray is less than that of the incident ray.
4)The image is much brighter.	4) The image is less bright and the bright ness as the silvering on miror becomes old and rough.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 3 Know About Some Common Gases offer valuable context and analysis.

WBBSE Class 8 Science Chapter 3 Question Answer – Know About Some Common Gases

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

Class 8 Science Chapter 3 Question Answer West Bengal Board – Know About Some Common Gases

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 (H_{2 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-

1. It is colourless, tasteless, odourless gas at ordinary temperature.
2. It is slightly heavier then air : Its denisty at normal temperature and pressure is 1.428 gram per litre.
3. It is slightly soluble in water: Solubility of oxygen at 0° C and 1 atm pressure is 14.8 mg per litre.
4. Freezing point of liquid oxygen is -218° C and boiling point is -183° C.
5. Oxygen has three isotopes, namely, , and though the natural abundance of the last two is very low.

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.

WBBSE Class 8 Science Chapter 5 Question Answer – Analysis of Natural Phenomena

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

Class 8 Science Chapter 5 Question Answer West Bengal Board – Analysis of Natural Phenomena

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 —

• We should try to take shelter inside a building, or even in a car or a truck. We should avoid taking shelter in sheds with metal roofing.
• Do not stand under a tree. As lighting tends to strike tall objects, the true has a possibility of getting struck by lightning.
• Do not run across an open field. Also, do not stand on high ground. Squat down on the low-lying ground if safe place cannot he found.

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 —

• Epidemic front common source : This types of epidemic is caused by any disease creating germ but not always (like poisoning of water, air, food or soil. Typical examples are Bhopal Gas Tragedy or Japanis Minamata disease).
• Epidemic from infection : Epidemic of this type is directly transmitted by one person to the other or through the medium of a living carrier of by infection front the body of living being (Measles, Small Pox, Influenza, Malaria)
• Slowly Infectious epidemic : Lung Cancer, Coronary heart Disease.

Detailed explanations in West Bengal Board Class 7 Science Book Solutions Chapter 5 Human Food offer valuable context and analysis.

WBBSE Class 7 Science Chapter 5 Question Answer – Human Food

(Page no. 145)

Let’s make a list of our daily work from the following pictures.
Answer:

(Page no. 147)

So, what kinds of food (plant/animal) do we eat? Which food component is less or excess in these food items? Discuss with your teachers and fill up the following chart from the discussions later on.

(Page no. 148)

Let’s make a chart showing food components present in different common foods. Take help from your teacher to fill up the following chart.

Food Source	Main Food elements
1. Rice, roti, milk, fruit, potato, sweet potato, honey, sugar, jaggery	Carbohydrate
2. Fish, meat, egg, milk, pulses, cheese, soyabean	Protein
3. Butter, ghee, coconut, groundnut, oil, animal fat. milk, fish	Lipid
4. Drinking water, fruits, vegetables, tea, milk, cooked food	Water
5. Tomato, amla, whole wheat grain, carrot, green vegetables, fruits	Vitamin
6. milk, salt, rice, molasseo, meat, leafy vegetables, milk, fish, pulses	Mineral
7. Mango, apple, oat, papaya, leafy vegetables, whole grains, pulses	Food fibre
8. Tea, ripe mango, ripe papaya, beet, pomegranate, watermelon	Phytochemical.

Page no. 150

Apart from the food items mentioned on the previous page some more are mentioned in the table below. Ask your teacher to know whether these contain carbohydrates or not.

Food	Present/Absent
1. Pumpkin	Present: 7gr./100gr.
2. Raisin             .	Present : 79gr./100gr.
3. Custard-apple	Present: 24gr./100gr.
4. Berry	Present: 14gr./100gr.
5- Egg	Present: 1.1 gr./100gr.
6. Cumin	Present: 44gr./100gr.
7. Curd	Present: 3.4gr./100gr.
8. Cake	Present: 59gr./100gr.
9. Ghee	Absent: 0gr./100gr.
10. Flattened rice	Present: 40gr./100gr.

(Page no. 152)

Apart from the food items mentioned above, some more mentioned in the table below. Ask your teacher to know whether these contain protein or not.

Food	Present/Absent
1. Rice/wheat	Present: 2.7gr./100gr, 12.61 gr./ 100gr.
2. Ghee	Absent: 0.3 8gr./100gr.
3. Groundnut	Present: 26gr./100gr.
4. Sesame	Present: 18gr./100gr.
5. Banana	Present: 1.1 gr./100gr.
6. Mushroom	Present: 3.1 gr./100gr.
7. Suji	Present: 13gr./100gr.
8. Ant eggs	Present: 8.2gr./100gr.

(Page no. 153)

Try to find out if lipid is present in the food mentioned in the table below.

Food / Drink	Present/Absent
1. Fruits and vegetables	Absent
2. Cereals	Absent
3. Tonnedmilk	Absent
4. Popcorn	Absent
5. Potato	Absent
6. Sugarcane juice	Absent
7. Lemon	Absent
8. Wheat, mazie, rice	Absent
9. Mushroom	Present
10. Chicken	Present
11. Dates	Absent

(Page no. 161)

Put the name of food components and their sources in the following table.

Food component	Food
1. Sugar	Rice, wheat, Bazra, potato, beat, carrot, sugar.
2. Protein	Fish, meat. egg. milk, pulse, soyabean, peas.
3. Lipid	Nut. coconut, ghee, butter, oil, fish, fat of meat.
4. Vitamin	Capsicum, tomato, green vegetables, gram, milk
5. Minerals	Green vegetables, food grain, soyabean, fish, meat, egg.
6. Water	All types of rinking water, fruit juice, coconut water
7. Fibre	Cereal, apple, oat, papaya, broccoli, figs, berries.
8. Plant chemical	Tea, cabbage, carrot, tomato, ripe mango

(Page no. 161)

Some physiological problems are mentioned. Which foods are required to prevent these health problems?

Problems	Which food should you have	Which food component will you get
Swollen gums with bleeding	Sour fruits, amla, lemon, guava	Vitamin C
Anaemic condition	Egg. milk, banana, guava	Vitamin B-complex
Weak and curved bones	Egg, milk, butter, cod liver oil	Vitamin-D
Constipation	Vegetables, cabbage, guava	Fibre
Short sight at night	Vegetables, milk, carrot, tomato	Vitamin-A
Ulcer in mouty and tongue	Egg, milk, spinach.	Vitamin B-complex
Wrinkled skin	Carrot, letus. egg, milk, raddish	Vitamin-A
Sudden rise in blood pressure	Small fish, vegetables, fruits	Sodium

(Page no. 162)

There are a few names of food. Try to find out which food components can you get from them. Take help from your teacher, if necessary.

• Ripe mango : Food fibre, sugar, vitamin
• Milk: Protein, vitamin, lipid, minerals
• Nuts : Lipid, vitamin, carbohidrate
• Egg : Protein, vitamin, lipid, minerals
• Guava : Vitamin, minerals, sugar
• Gurd : Vitamin, minerals, sugar
• Tomato : Vitamin, plant chemicals
• Rice : Carbohidrate, vitamin
• Spinach : Vitamin, minerals, foodfibre
• Amla : Vitamin, minerals

(Page no. 166)

Following symptoms develop due to defficiency of different food components. Write down the names of food items that can prevent these diseases.

Symptoms	Defficiencyof food component	Somponents are found in
Bent limbs	Vitamin D	Milk, egg, butter, fish
White spot in iris	Vitamin A	Carrot, egg, milk, curd, letus
Can’t read blackboard	Vitamin A	Carrot, egg, milk, curd, letus
Ulcer on tongue, nouth	Vitamin B Complex	Vegetable, cabbage, milk, green chilli
Swollen face	Protein	Milk, fish, meat, panir, soyabean
Broken nails	Calcium	Milk, amla, lemon, guava
Rough skin	Vitamin A	Carrot, egg, milk, curd, letus

(Page no. 166)

Weight and height of some children and adults are mentioned below. Calculate BMI from it.

Weight (kg)	Height (m)	BMI (weight/height2)	Obese yes/no	Synptoms
62	1.57	25.15	no	normal
66	1.50	29.33	yes	high blood pressure, asthma
72	1.59	28.47	yes	(respiratory problem, diabetes
64	1.62	24.38	no	normal
75	1.60	29.29	yes	high blood pressure, asthma
71	1.58	28.44	yes	knee pain, asthma
72	1.67	25.81	no	normal

Class 7 Science Chapter 5 Question Answer West Bengal Board – Human Food

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

Question 1.
Which is known as instant source of energy ……………………….
i) starch
ii) vitamins
iii) minerals
iv) glucose
Answer:
iv) glucose

Question 2.
Dificiency of iron in our diet casues ……………………….
i) scurvy
ii) anaemia
iii) goitre
iv) blindness
Answer:
ii) anaemia

Question 3.
Plants manufacture food in the form of ……………………….
i) starch
ii) fructose
iii) glucose
Answer:
iii) gluuose

Question 4.
What helps in removing wastes from the body ……………………….
i) water
ii) protein
iii) glucose
iv) phytochemical
Answer:
i) water

Question 5.
Starch is a complex ……………………….
i) mineral
ii) lipid
iii) glucose
iv) carbohydrate
Answer:
iv) carbohydrate

Question 6.
Daily requirement of carbohydrate by an adult is ……………………….
i) 500 gram
ii) 300 gram
iii) 600 gram
iv) 100 gram
Answer:
i) 500 gram

Question 7.
Marasmus is due to the deficiency of ……………………….
i) vitamin C
ii) carbohydrate
iii) fat
iv) protein
Answer:
iv) protein

Question 8.
To get sufficient carbohydrate one should take ……………………….
i) meat
ii) rice
iii) carrot
iv) ground nut
Answer:
ii) rice

Question 9.
What one of the following is the best source of vitamin-A?
i) egg
ii) honey
iii) carrot
iv) pea nut
Answer:
iii) carrot

Question 10.
Fat soluble vitamins are ……………………….
i) A D E and K
ii) B C and D
iii) D B and E
iv) A B and C
Answer:
i) A D E and K.

Question 11.
Vitamin essential for blood clotting is ……………………….
i) A
ii) E
iii) C
iv) K .
Answer:
iv) K

Question 12.
Which one is body-building material?
i) mineral
ii) Protein
ii) fat
iv) sugar
Answer:
ii) Protein

Question 13.
Scurvy disease causes in deficiency of vitamin ……………………….
i) C
ii) B
iii) K
iv) A
Answer:
i) C

Question 14.
Artificial chemical Ajinamoto is used to make ……………………….
i) chocolate
ii) popcorn
iii) momo
iv) tea
Answer:
iii) momo

Question 15.
Trans-fat is present in ……………………….
i) pastry
ii) potato chips
iii) cotton
iv) coffee
Answer:
ii) potato chips

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

1. ………….. provides us energy for all life activites.
Answer:
Food

2. Food keeps us healthy and enables us to fight against …………..
Answer:
diseases.

3. In the process of digestion starch a ………….. is broken down into the smallest unit (Glucose).
Answer:
complex carbohydrate.

4. Energy is produced in the cells of the healthy body by break down of …………..
Answer:
glucose.

5. ………….. is caused due to the lack of food fibre in our diet.
Answer:
Constipation

6. The protein that is present in hair and nail is ……………
Answer:
keratin.

7. The protein present in blood is …………..
Answer:
Haemoglobin.

8. ………….. has important role in providing immunity.
Answer:
Protein.

9. ………….. help in coagulation of blood oozing out continuously from any wounded region.
Answer:
Plasma proteins.

10. ………….. reduces heat emission from human body.
Answer:
Lipid.

11. Vitamins A D E and K are …………..
Answer:
Fat-soluble.

12. B-complex and C vitamins are ………….. vitamins.
Answer:
water-soluble.

13. Vitamin ………….. helps to maintain the structure of eye skin bones and teeth.
Answer:
A

14. Vitamin …………… maintains the structure of bones and joints.
Answer:
D

15. Deficeincy of iron causes ……………
Answer:
Anaemia.

16. …………… controls mental abilities and mental growth.
Answer:
Iodine.

17. Deficiency of …………… causes increase in blood sugar level.
Answer:
zinc.

18. The …………… part of food comes out of the body as stool.
Answer:
undigested.

19. Excessive water loss from the body causes ……………
Answer:
dehydration.

20. Deficiency of proteins lipids and carbohydrates in the diet casues …………..
Answer:
Marasmus.

21. Protein malnutrition results in a disease called …………..
Answer:
Kwashiorkar.

22. The kitchen of plant is …………..
Answer:
leaf.

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

1. High blood pressure is related with iodine.
Answer:
false

2. Iodine controls mental abilities and mental growth.
Answer:
true

3. Sodium maintains water level in body.
Answer:
true

4. Source of iodine is vegetables.
Answer:
false

5. Iron helps in transporting oxygen in tissues.
Answer:
true

6. Plant source of lipid is fish oil..
Answer:
false

7. Keratin is present in hair and nail.
Answer:
true

8. Collagen is present in tendon and ligament.
Answer:
true

9. Protein is the main food component of ground nut butter coconut.
Answer:
false

10. Deficiency of vitamin causes ulcer at the corner of lips.
Answer:
true

11. Due tr deficiency of iodine symptom of high blood pressure is seen.
Answer:
false

12. For deficiency of vitamin A.one can not read blackboard from the last bench.
Answer:
true

13. Processed foods are richest in nutritional value.
Answer:
false

14. The foods obtained directly from mature are called natural foods.
Answer:
true

15. About 75% of earth’s surface is covered by water.
Answer:
true

Match the column A with column B

Column A	Column B
a) Aquatic plants absorb water	i) 60% water by mass
b) High fever occurs in	ii) is the cause of blindness
c) Human body has	iii) which can not be digested
d) Natural foods are richest	iv) from plants or animals or from water
e) Deficiency of Vitamin A	v) with their whole body
f) We get phytochemicals	vi) Malaria or Pneumonia
g) Stool has fibres	vii)root and other parts
h) Plant absorb water through	viii) in nutritional value
i) Deficiency of iodine	ix) from tomato                        ‘
j) Animals get minerals              .	x) causes goitre

Answer:
a) Aquatic plants absorb water with their whole body.
b) High fever occurs in Malaria or Pneumonia.
c) Human body has 60% water by mass.
d) Natural foods are richest in nutritional value.
e) Deficiency of Vitamin A is the cause of blindness.
f) We get phytochemicals from tomato.
g) Stool has fibres which can not be digested.
h) Plant absorb water through root and other parts.
i) Deficiency of iodine causes goitre.
j) Animals get minerals from plants or animals or from water.

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

Question 1.
What is needed to do daily work?
Answer:
Energy is needed to do daily work.

Question 2.
What is the source of energy in our body?
Answer:
Healthy and balanced diet is the source of energy in our body.

Question 3.
Which is ‘energy giving food’?
Answer:
Carbohydrates are energy giving food.

Question 4.
Which is ‘body building food’?
Answer:
Protein is body building food’.

Question 5.
What are protective foods?
Answer:
Vitamins and minerals are protective foods.

Question 6.
Name some plant sources which supply carbohydrate.
Answer:
Rice, wheat, potato, beet, pulses etc. are some sources which supply carbohydrate

Question 7.
Name some animal sources which supply carbohydrate?
Answer:
Honey, milk, meat, liver etc. are some animal sources which supply carbohydrate.

Question 8.
Which disease occurs due to unavailability of glucose in cells?
Answer:
Diabetes Mellitus occurs due to unavailability of glucose in cells.

Question 9.
What are the functions of muscles of our hands?
Answer:
Muscles of hand help to lift, push, pull things.

Question 10.
What are the functions of muscles of our legs?
Answer:
Muscles of leg help in walking, running, climbing jumping etc.

Question 11.
What is the function of Heart?
Answer:
Circulation of blood in our body.

Question 12.
What is the function of Lungs?
Answer:
It helps in respiration.

Question 13.
What is the function of Intestine?
Answer:
Digestion of food is the function of Intestine.

Question 14.
Name the protein present in hair and nail?
Answer:
Keratin is present in hair and nail.

Question 15.
Name the proteins present in muscle?
Answer:
Actin, Myosin.

Question 16.
Name the protein present in Red Blood Corpuscle?
Answer:
Haemoglobin.

Question 17.
Which proteins are in blood plasma?
Answer:
Globulin. Fibrinogen.

Question 18.
Collagen protein is present in which body parts?
Answer:
Bone. Tendon, Ligament.

Question 19.
Nans some plant sources which supply protein.
Answer:
Pea, kindney bean, seeds of jackfruit, millet, corn, garlic, clove, turmeric etc.

Question 20.
Name some animal sources which supply protein.
Answer:
Ghana, Paneer, Crab, milk, meat, fish, eggs etc.

Question 21.
Name some plant sources of lipid.
Answer:
Coconut, jackfruit, vegetable cooking oil, whole wheat grain etc.

Question 22.
Name some animal sources of lipid.
Answer:
Fish oil, milk, curd, meat, ghee, butter, egg yolk, meat, cheese etc.

Question 23.
Beri-Beri causes due to lack of which vitamin?
Answer:
Vitamin B.

Question 24.
Which vitamin deficiency disease was common in Europe nearly 500 years ago?
Answer:
Scurvy.

Question 25.
Which vitamin deficiency casues scurvy?
Answer:
Vitamin C.

Question 26.
Which vitamin helps in blood clotting?
Answer:
Vitamin K.

Question 27.
Which plant sources supply vitamins?
Answer:
Ripe mango, pumpkin, fig, tomato, spinach, cabbage and other green leafy vegetables.

Question 28.
Which animal sources supply vitamins?
Answer:
Meat, ghee, eggs, milk, fish, etc.

Question 29.
Name some sources of vitamin B complex.
Answer:
Cereals, cabbage, leaves of raddish, small fishes, chili, milk etc,

Question 30.
Name some essential minerals which our body requires.
Answer:
Iron, Calcium, Magnesium, Sodium, Iodine, Zinc etc.

Question 31.
Which parts of the plant produce food?
Answer:
Food is produced in leaves and other green parts.

Question 32.
What is the right amount of water that one drink daily?
Answer:
A healthy adult shout eat 50 ml/kg body weight to meet the daily requirement.

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

Question 1.
What is food? Why is food essential?
Answer:
The source of our energy and disease resistant component is food.
All living beings need energy to remain alive and active. The food we eat provides us with energy as well as those things that our body needs to stay alive and healthy.

Question 2.
What are the main components of food?
Answer:
The main components of food are –

• Carbohydrate
• Protein
• Lipid
• Vitamin
• Water
• Mineral
• Food fibre
• Phytochemical.

Question 3.
Define macronutrients and micronutrients.
Answer:
Carbohydrates, fats and proteins make up to bulk of our food. They are called macronutrients.
Vitamins and minerals though crucial for health, are needed in small quantities. They are called micronutrients.

Question 4.
Why Food fibres and water are also important components of our food?
Answer:
Food fibres from the roughage part of our food. They help in the movement of bowel in the intestine. Water helps our body to absorb nutrients from the food. It also helps in removing wastes from the body.

Question 5.
Mianly how many types of carbohydrate are there in our food?
Answer:
Carbohydrate which we get from our food to keep us strong is mainly of two types— glucose and starch.

Question 6.
How is energy produced in our body?
Answer:
Energy is produced in the cells of the healthy body by breakdown of glucose. That energy is required for different works.

Question 7.
‘Sometimes intake of milk causes problem’, — What is the reason behind it?
Answer:
Some children or aged persons suffer from different problem after intake of milk or milk products. Indigestion of leactose, a milk carbohydrates, leads to this type of problem.

Question 8.
What leads to obesity? In which body parts lipid is stored in huge amount in an obese person?
Answer:
Eating more of energy-rich food than required by the body causes I ipid deposition in the body and leads to abesity. Lipid containing body parts are neek, upper arm, chest, abdomen and thigh, in an obese person.

Question 9.
How is lipid important? What problem will arise if lipid is stored more than necessary?
Answer:
Lipid acts as sources of energy in the human body and protects the body from external injury. It also reduces heat emission from human body. If more than necessary lipid is stored, the condition can create different problems in heart, blood vessel and liver.

Question 10.
How many types of vitamins are there?
Answer:
Vitamins are of two types—

• Fat-soluble vitamin—A, D, E and K.
• Water-soluble vitamin—B complex and C.

Question 11.
Name some natural pigments which are present in food from plant sources. How are they helpful to us?
Answer: Some coloured pigments present in plant sources are caroteinoids, flavonoids. They stop fast ageing of human body, keeps healthy functioning of heart, strengthen bones. They also check cancer.

Question 12.
What is balanced diet?
Answer:
The diet which contains all the essential nutrients in just the right proportion is called a balanced diet. It varies from person to person depending upon sex. age, group of profession.

Question 13.
What are the symptoms of malnutrition in the child?
Answer:

• Decay of bone in body.
• Muscle is distinct from outside.
• Skin is wrinkled here and there.
• Hands and legs are thin.

Question 14.
Below write the names of different dificiency diseases.
1. Iron dificiency = —
2. Iodine deficiency = —
3. Vitamin D deficiency = —
4. Vitamin B complex deficiency = —
5. Vitamin A dificiency = —
6. Deficiency of protein and energy = —
Answer:
1. Anaemia
2. Goitre, mental retardation, squint
3. Ricket
4. Beriberi
5. Blindness
6. Marusmus, Kwashiorkar.

Question 15.
Why artificial food should not be taken in huge quentity?
Answer:
Artificial food is highly priced by the nutrient level in near by nil. Over consumption of these foods leads to problem of heart, liver, kidney, bones or brain.

Question 16.
What are the symptoms of low blood pressure?
Answer:
Hyponatremia ossures when sodium levels in the blood are too low. Symptoms include lethargy, confusion, and fatigue.

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

Question 1.
Why the diseases Mamasmus and Kwashiorkar occur?
Answer:
The disease caused by malnutrition is called Marusmus. Deficiency of protein and energy in diet lead to this disease. This is predominant in children below one year. Kwashiorkar disease develops in children of 1-4 years old due to deficiency of protein. Children . suffering from Kwashiorkar show stunted growth, large potlike belly, mental retardation swollen face and dark skin.

Question 2.
What can be the reason of obesity? What are the effects of obesity?
Answer:
Obesity occurs due to excessive intake of junk food like pizzas, potato wafers, noodles, icecream and soft drinks which contain excessive lipid. Viewing of TV instead of playing outdoor games, is another cause of obesity. Obese persons are prone to heart disease and high blood pressure (hypertension), ft leads to arthritis, diabetes and anaemia. Obesity also causes discomfort and breathlessness.

Question 3.
When malnutrition occurs?
Answer:
The chance of malnutrition increases if deficiency of energy producing food components are found in diet. Energy producing food components are carbohydrate, protein and lipid. Deficiencv of other food components (vitamin and mineral) also lead to many problems. Worms can be a reason for malnutrition.

Question 4.
Discuss role of water and light in production of food in plants.
Answer:
Plant absorbs water through root and other parts, sends the absorbed water to leaves. Plant absorbs a small amount of light energy from sunlight. Plants begin the process Photosynthesis with the help of light energy and green pigment chlorophyll. Food is produced in leaves and other green parts by water, sunlight and carbon dioxide absorbed from air.

Question 5.
Describe the importance of water in our body.
Answer:
Water is needed for the following functions :

• It maintains our body temperature.
• It is needed in the excretion of wastes.
• It acts as a medium for biochemical reactions in our body.
• It helps in the transportation of nutrients within the body.
• It is an essential part of digestive juices and blood.

Question 6.
What is fibre? How is food fibre helpful?
Answer:
Fibre is a type of Carbohydrate of the nature of cellulose or protein. These may or may not be dissolved in water. The food fibres are formed of cellulose. Since we cannot digest cellulose, human body cannot yield energy from food fibres, it also does not provide us any nutrients.

They simply add bulk to our food and help to get rid of undigested food. Therefore, food fibre help in proper digestion of food as well as in easy and regular movement of bowel. This prevents constipation, colon cancer, obesity high blood pressure and reduces acidity in the stomach.

Question 7.
What will happen if glucose does not enter into cell from blood?
Answer:
Glucose then circulates through blood till it excretes out from the body through kidney. Different organs (heart, kidney, eye, leg) malfunction due to unavailability of glucose in cells. This condition is termed as Diabetes Mellitus. This disease is very common in India. Proper diet and regular exercise can help to prevent this disease.

Question 8.
Why are minerals necessary? Mention some of its function.
Answer:
Minerals are necessary for proper growth of body and to maintain good health, like vitamins, minerals does not supply energy to our body. Some functions are —

• Calcium — maintains muscle contraction, helps in blood coagulation.
• Sodium — maintains water level in body.
• Iron — helps in transport of oxygen, needed for the formation of red blood cells.
• Iodine — controls mental abilities and mental growth.
• Zinc — maintains brain functioning and blood sugar level.
• Calcium, Phosphorus, Magnesium — develop bones and teeth.

Question 9.
Name some minerals necessary for our body. How do plants and animals obtain these minerals?
Answer:
Some minerals necessary for our body are — Iron, Calcium, Magnesium, Sodium, Potassium, Zinc etc.
The minerals are obtained from living organisms as well as non-living compounds.

• Plants collect minerals from soil or ground water under soil.
• Animals get minerals from plant foods, animal foods or water.

Question 10.
What would happen if body looses excessive water? What precautions should be taken then?
Answer:
Excessive water loss from the body causes dehydration. Due to dehydration blood becomes thicker, causing severe pain and cramps. In order to make up the loss of water and minerals from the body, we should drink a solution prepared by adding one teaspoonful of sugar and a pinch of salt to 200 ml of water. This solution is called Oral Rehydration Solution (ORS).

Question 11.
What is starch? How is glucose important to our body?
Answer:
Starch is a complex carbohydrate. In the process of digestion, starch, is broken down into the smallest units (Glucose). This glucose is transported to peripheral regions through blood. Here the absorbed oxygen helps in production of energy from glucose in body. This energy helps in different performances.

Question 12.
Describe the importance of protein in our body. What will happen if there is excess protein in our body?
Answer:
Different kinds of proteins play important roles in producing energy, formation of tissue or parts of body, healing wounds, transport of respiratory gases, contraction of muscles. Protein has important role in providing immunity. Plasma proteins help in coagulation of blood oozing out continuously from any wounded region. Excess protein in body can lead to arthritis, renal stone and other problems.

Question 13.
Which vitamins (A, D, E, K) are needed in the following cases?
Answer:

Problems	Vitamin
1. Short sight at night	A
2. Curved bones and curved vertebral column	D
3. blood doesn’t easily coagulate in wounded areas	K
4. Damage of red blood cells, heart, brain activity hampered	E

Question 14.
Symptoms are given write down the names of water-soluble vitamin necessary.
Answer:

Symptoms	Vitamin
1. Cracked lips	B-complex
2. Nails and lower part of eye becomes pale	B-complex
3. Loosening and falling of tooth	C
4. Nervous disorder	B-complex
5. Loose motion, Demensia	B-complex

 

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 11 Plant Kingdom and the Environment Around Us offer valuable context and analysis.

WBBSE Class 8 Science Chapter 11 Question Answer – Plant Kingdom and the Environment Around Us

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

Question 1.
Every year each water hyacinth produces seeds —
i) less than five hundred
ii) less than thousand
iii) more than thousand
iv) less than hundred
Answer:
iii) more than thousand

Question 2.
Now-a-days bamboo fabrics are used for making —
i) clothes
ii) papers
iii) ropes
iv) medicines
Answer:
i) clothes

Question 3.
Resin derived from sal tree are used for making —
i) shoe polish
ii) gum
iii) chocolates
iv) spirit
Answer:
iv) spirit

Question 4.
Now laws are framed to protect —
i) Sal plant CL
ii) Sundari plant
iii) Bamboo plant
iv) water Hyacinth
Answer:
ii) Sundari plant

Question 5.
We get cinnamon from —
i) bark of tree
ii) fruits of tree
iii) flower of tree
iv) seeds of tree
Answer:
i) bark of tree

Question 6.
Black peeper is used in —
i) nausea
ii) diarrhoea
iii) cold
iv) liver diseases
Answer:
iii) cold

Question 7.
Curcumin is found in —
i) Cinnamon
ii) ginger
iii) garlic
iv) turmeric
Answer:
iv) turmeric

Question 8.
Ginger is useful in —
i) gum problem
ii) stomach upset
iii) anemia
iv) pain in gum
Answer:
ii) stomach upset

Question 9.
A compound called Alicin is rerived from —
i) ginger
ii) cardamom
iii) garlic
iv) turmeric
Answer:
iii) garlic

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

1. Bamboo is one of the lowest growing tree of the world.
2. Different bamboo-made utensils are used for the purpose of cooking.
3. Water hyacinth is a good source of biogas as it contains high amount of oxygen.
4. Sal is a type of coniferous tree.
5. The fruit of Sundri plant is egg-like but is slightly elongated.
6. Spices were used to preserve meat.
7. Ginger and Turmeric are fruits of plant.
8. Saffron is floral part of plant.
9. Cinnamon is prepared by drying leaf of the cinnamon tree.
10. Turmeric is also used to dye different foods and medicines.
Answer:
1) false
2) true
3) false
4) false
5) true
6) true
7) false
8) true
9) false
10) true.

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

1. Plants are sources of ………….. as well as ………….. for animals also.
2. ………….. is one of the fastest growing tree of the world.
3. The major food of Gorillas of Africa is …………..
4. ………….. an importanit medicine is derived from inter mode of bamboo species namely
5. ………….. mosquitoes propagate in the densely grown water hyacinth plants.
6. ………….. derived from bank of Sal are used in leather industry.
7. Sundri trees grow in sweet water of saline areas of ……………
8. Apart from enhancing the taste of food spices are also used as ………….
9. Clove contains a chemical substance called ………….. which has anti-bacterial properties.
10. In different countries of the world almost …………. types of spices are cultivated.
11. Black pepper is a perenuial …………..
12. ………….. is responsible for the hot taste of black pepper.
13. Cinnamon is prepared by drying the ………….. of the cinnamon tree.
14. ………….. is a peremial herb.
15. A compound, called ………….. is found in turmeric.
16. Seeds of greater cardamom alleviates …………..
17. Each bulb of garle is termed as ………….. of garlic.
18. Garlic contains a compound called ……………
19. At present around species of medicinal plants are found in our country.
20. Juice of neem leaves is very useful for……………
21. Bael fruit contains ………….. and ………….., which is a panacea for constipation.
22. Emblica fruit contains huge amount of ……………
23. ………….. leaves are useful in bleeding haemorrhoids and wasp sting.
24. Mint sherbat is a useful digestive for ………….. troubles.
25. Extract of aloevera leaves is used to reduce ………….. and …………..
Answer:
1) shelter, food
2) Bamboo.
3) bamboo
4) Tabashir. Bambusa arundinacea.
5) Aedes
6) Tannin
7) Sunderban
8) preservative
9) Eugenol.
10) eighty
11) vine
12) Piperine
13) inner, bark
14) Turmeric
15) curcumin
16) nausea
17) grates
18) Alicin
19) 3500
20) diabetes
21) mucilage, pectin
22) Vitamin C
23) Cantharanthus
24) stomach
25) mental stress, tension.

Match the column A with column B.

Column A	Column B
a)  Neem oil is used for b)  Unripe bael increases c) Catharanthus leaf is a good nedicine d)  Extract of aloevera leaves is used e) Garlic is effective in f) Cardamom is used in preparing g) Turmeric has the ability h) Cinnamon has its own	i) for diabetes ii) various problem of heart iii) different sweet dishes iv) to kill bacteria v) sweet aroma and taste vi) pain in ear vii) appetite and digestive power viii) in constipation

a) Neem oil is used for pain in ear.
b) Unripe bael increases appetite and digestive power.
c) Catharanthus leaf is a good nedicine fordiabetes.
d) Extract of aloevera leaves is used in constipation.
e) Garlic is effective in various problem of heart.
f) Cardamom is used in preparing different sweet dishes.
g) Turmeric has the ability to kill bacteria.
h) Cinnamon has its own sweet aroma and taste.

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

Question 1.
Name one of the fastest growing tree of the world.
Answer:
Bamboo

Question 2.
How is the stem of bamboo?
Answer:
Stem are long pipe-like and with less branches.

Question 3.
What is the rate of growth in some species of bamboo plant?
Answer:
100 cm in each 24 hour.

Question 4.
Name some endangered animals whose cheif food is different part of bamboo.
Answer:
Giant panda of china, Red panda of Nepal and India and Lemur of Madagascar.

Question 5.
How hollow stems of bamboo are used in different places of South Africa.
Answer:
For warming soups and as pot for cooking rice.

Question 6.
For how many years water hyacinth live?
Answer:
For 24 years.

Question 7.
Name some countries where the stems of water hyacinth arc used for the purpose of embroidery and garment industries.
Answer:
Philippines. Thailand and Vietnam.

Question 8.
How many years Sal take to mature.
Answer:
25 to 30 years.

Question 9.
Name a plant in which stilt root is present.
Answer:
Sundri

Question 10.
How the fruit of Sundri plant look like?
Answer:
The fruit of Sundri plant is egg like but is slightly elongated.

Question 11.
What is the colour of Sundri plant fruit?
Answer:
Brownish.

Question 12.
Name a centre for rearing and conserving Sundri plant.
Answer:
Jharkhali.

Question 13.
Name some places where Indian spices, perfumes and fine clothing materials travelled in past?
Answer:
Mesopotemia, Arabia and Egypt.

Question 14.
What chemical substance present in clove has anti-bacterial properties?
Answer:
Clove contains a chemical substance Eugenol, which has anti-bacterial properties.

Question 15.
Name some spices which arc seeds of plant.
Answer:
Ajowan, Fennel, Coriander, Mustard, Poppy seeds. Aniseed.

Question 16.
Name a plant whose seed is used as spies.
Answer:
Clove.

Question 17.
Name some rhizomes used as spices.
Answer:
Ginger, Turmeric.

Question 18.
Which part of plant is Asafoctida spice?
Answer:
Exudates.

Question 19.
Name some leaves used as spices.
Answer:
Cassia leaf (Tejpata), Mint.

Question 20.
Name some fruits of plant used as spices.
Answer:
Black pepper, Cardamom, Chillies.

Question 21.
Name a kernel of plant used as spices.
Answer:
Nutmeg.

Question 22.
What is the colour of Black pepper when it is unripe and after ripening?
Answer:
Unripe fruits of Black pepper are green and become reddish in colour after ripening.

Question 23.
When Black pepper turns black?
Answer:
The ripe fruit becomes black when they are dry.

Question 24.
What is the taste of Black pepper?
Answer:
The taste of Black pepper is hot.

Question 25.
What is responsible for the hot taste of Black pepper?
Answer:
Piperine is responsible for the hot taste of Black pepper.

Question 26.
How is cinnamon prepared?
Answer:
Cinnamon is prepared by drying the inner bark of the cinnamon tree.

Question 27.
How many types of Cinnamon are there?
Answer:
Two types – thick bark and thin bark.

Question 28.
What compound is found in turmeric?
Answer:
Curcumin compound.

Question 29.
How the presence of Curcumin compound in turmeric is helpful?
Answer:
Due to its presence, turmeric has the ability to kill bacteria, viruses and fungi.

Question 30.
Why is Turmeric effective in anemia?
Answer:
Turmeric is effective in anemia due to the presence of good amount of iron in turmeric.

Question .
How many types of Cardamom arc there?
Answer:
Two types -greater cardamom and lesser cardamom.

Question 32.
What is the colour of dried greater cardamom and lesser cardamom?
Answer:
Dry Greater cardamom is coppery in colour and dry lesser cardamom is light brown in colour.

Question 33.
Why fully ripe fruits of cardamom not selected for artificial drying?
Answer:
Suice ripe fruits may burst while being dried.

Question 34.
Generally how Garam Masala is prepared?
Answer:
Garam Masala is prepared by mixing clove, cardamom, cinnamon, black pepper, mace and nutmeg.

Question 35.
What arc grates of garlic?
Answer:
A bulle of garlic consists of 6-30 small bulb-like parts. These are termed as grates of garlic.

Question 36.
Name the compound present in Garlic?
Answer:
Alicin compound is present is Garlic.

Question 37.
Which veda describes the medicinal properties of different plants?
Answer:
Atharva Veda.

Question 38.
According to WHO what percent of population depend on traditional medicines for primary treatment?
Answer:
80% population.

Question 39.
How many species of medicinal plant is found only in Asia?
Answer:
8,500 species.

Question 40.
At present how many types of medicinal plant is present in our country?
Answer:
3,500 species.

Question 41.
How is Bael fruit helpful for constipation?
Answer:
Bael fruit contains mucilage and pectin, which is a pancea for constipation.

Question 42.
What is Triphala?
Answer:
Triphala is kind of ayurvedic medicine.

Question 43.
How many fruits are present in Triphala?
Answer:
Three fruits – Emblica, Chebulic myrobalan (Haritaki) and Belleric myrobalan (Bahera) (without seed).

Question 44.
Name the alkaloid present in the root of Catharanthus (Nayantara) helpful in removing obstacles in blood circulation in brain?
Answer:
Raubasine.

Question 45.
Name two alkaloids present in Catharanthus helpful in treatment of Cancer?
Answer:
Vincristine mid Vinblastine.

Question 46.
What aioevera leaves contain?
Answer:
Aioevera leaves contains vitamins, minerals, amino acid and fatty acid.

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

Question 1.
In middle ages what was the utility of spices?
Answer:

• There was no refrigerator in that age. So spices were used to preserve meat,
• Spices enhanced the taste of food.

Question 2.
Mention two medicinal properties of Bael fruit.
Answer:

• Bael fruit contains mucilage and pectin, which is a panacea for constipation,
• Juice of bael fruit takes care of intestine of diarrhoea patients.

Question 3.
How do we get spices?
Answer:
We get spices from different parts of plants. Such as — cinnamon from bark of tree, clove from buds, black peeper, cardamom from fruits, tejpata mint from leaves, ajowan aniseed fennel from seeds, nutmeg from kernel.

Question 4.
Write two medicinal value of ginger.
Answer:
Ginger is useful in stomach upset, heartburn or problems related to gas, cough and asthma. Taking pieces of ginger with salt before eating specially in monsoon or winter season, increases appetite.

Question 5.
How black peeper looks like?
Answer:
Its unripe fruits are green and become reddish in colour after ripening. The ripe fruit becomes black when they are dry.

Question 6.
What is the medicinal value of bamboo?
Answer:
Tabashir, an important medicine for asthma, cold and cough and many infestious disease <s made from silicon dioxide and silicic acid. These are derived from intermode of bamboo spscies namely Bambusa arundinacea.

Question 7.
Can water hyacinth be used in industries?
Answer:
The items of witter hyacinth are used for the purpose of embroidery and as a source of fibres for garnish dustries in many countries of the world. Fibres of it are being used in paper manufacturing.

Question 8.
Mention two uses of emblica.
Answer:

• Emblica works well in nausea and constipstion.
• Emblica is effective in prevention of anemia and cancer.

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

Question 1.
How are plants useful to us?
Answer:

• Animals utilise oxygen, exhaated by plants, for their respiration.
• Plants serve as a source of shelter as well as food for animals.
• Plants reduce the extent of pollution by absorbing pollutants.
• Plants impart different roles for controlling temperature, rainfall, wind velocity.
• Different parts of plants are being used as raw materials for different industries.
• Parts of some plants or even the whole plant body are used as manure.

Question 2.
Mention any four uses of bamboo plant?
Answer:

• The young stem, basal part of stem and leaves of bamboo plants are chief foods of many critically endangered animals of world.
• Different delicious dishes are being prepared at different countries of Asia using soft young stems coming out from the base of bamboo.
• In India bamboo is used for manufacturing paper, baskets, handle of umbrella, flower vase, tray, flutes, different types of toys and for interior decoration of rooms.
• Tabashir, an important medicine for asthma, cold and cough and many infectious diseases is made from silicon dioxide and silisic acid derived from internode of bamboo species namely Bambusa arundinacea.

Question 3.
Write three uses of water Hyacinth.
Answer:

• Water hyacinth is a good source of biogas as it contains high amount of nitrogen.
• Abater hyacinth is a tolerant species of plant. It can purify polluted dirty water by absorbing
  heavy metals like Cadmium, Chromium, Cobalt, Nickel, Lead and Mercury. As a result water become pollutant free and become suitable for us for different purposes.
• The demand for water hyacinth as fodder is increasing day by day as it contains high amount of protein or nitrogen.

Question 4.
Write three different uses of Sal plant.
Answer:

• Sal tree are of greater use in making poles, furniture, frame of doors and windows, floor of boats, jetty of the ship and foot bridge over rivers.
• From the gum of Sal tree red resius with fragrance are derived. These resins are used for

Question 5.
For what purposes we use spices?
Answer:

• To bring taste to bland food items.
• Use it as preservative (in pickles, Chutneys etc).
• Helps in digestion by increasing salivation.
• Helps keeping the mouth-cavity germ-free.

Question 6.
Write two uses of Black pepper and Cinnamon.
Answer:
Uses of Black pepper —

• Black pepper is used in cough, toothache, bleeding from the gum pain in gum and indigestion.
• Black pepper is used as preservative for meat and other perishable food items.

Uses of Cinnamon —

• Cinnamon is used in small pieces or in powdered form in cooking.
• In diarrhoea, nausea, vomitting and for cold, cinnamon is useful.

Question 7.
Write three medicinal uses of turmeric.
Answer:

• Turmeric helps in keeping the liver health
• Turmeric is effective in anemia due to the presence of good amount of iron in turmeric.
• Due to the presence of Curewntn compound in turmeric, it has the ability to kill bacteria, viruses fungi.

Question 8.
How is Cardamom useful to us?
Answer:

• Cardamom has its use in stomach related problems.
• Cardamom is taken with bital leaf and also as a mouth freshner.
• Greater cardamom strengthens gum.
• Seeds of greater cardamom alleviates nausea.

Question 9.
Mention some uses of Garlic.
Answer:

• Alicin compound in Garlic has anitmicrobial properties.
• Garlic helps to alleviate gas related problem.
• Garlic helps in food digestion, by stimulating the stomach.
• it is effective in various problems of heart and blood vessels.

Question 10.
How the different parts of neein tree like — Steam, leaves, root etc are important to us?
Answer:

• Juice of neem leaves is very useful for diabetes,
• Neem seed has its use in viral epidemic and arthritis.
• Neem oil extracted from leaves and stem is used for pain in ear, as well as gum and toothache. It is also used to maintain the health of hair, to increase the working capacity of the liver and as a blood cleanser.
• The bitter tonic prepard from the bark of root and stem is useful in breaking the periodic sequence of fevers (like malaria). It has its use also in skin diseases.

Question 11.
Write medicinal properties of Embiica fruit.
Answer:
Embiica fruit contains huge amount of Vitamin C. Embiica fruit is useful in the swelling of gum. Dry empirical fruit is capable to stop stomach upset, hemorrhage and dysentery. Embiica works well in nausea and constipation. It is effective in prevention of anemia and cancer.

Question 12.
What is Triphala? How is it useful?
Answer:
Triphala is a kind of ayurvedic medicine. Triphala contains three fruits Embiica (Amtaki), Chebulic myrobalan (Haritaki) and Belleric myrobalan (Bahera) (without seed). Powdered triphala is used as purgative which helps to clean the alimentary canei. Triphala is used as a blood-cleanser. Triphala contains Vitamin C. for this reason triphala is used as supplementary food.

Question 13.
How are alkaloids present in Catharanthus useful?
Answer:
An alkaloid called Raubasine is present is the root of this plant and it helps to remove obstacles in blood circulation in the brain. Vineristine and Vinblastine two alkaloids present in Catharanthus are presently used to treat blood cancer and certain other types of cancer. These two aikoioids are also effective in restraining tumour growth.

Question 14.
Write two medicinal properties of Mint (Pudina) and Aloevera.
Answer:
Mint (Pudina) —

• Mint is useful in flatulence, indigestion, loose stool of infants and bad breath.
• Mint is useful in cough, loss of appetite and inflammation of stomach.

Aloevera —

• Extract of aloevera leaves is used to reduce excess of acidity, tendency of blood to become thick, stress due to pollution and inflammation of bone joints.
• Extract of aloevera is used in fever to reduce temperature as it contains an anti-pyretic component.

Detailed explanations in West Bengal Board Class 8 Science Book Solutions Chapter 2.4 Chemical Effects of Electricity Reaction offer valuable context and analysis.

WBBSE Class 8 Science Chapter 2.4 Question Answer – Chemical Effects of Electricity

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.