Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8

Class 8: Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8

The document Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8 is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8

Ques 1: Choose the correct option:
(i) Identify the statement which is true for cells:

(A) Cells can be easily seen with naked eyes.
(B) Insect?s egg is not a cell.
(C) A single cell can perform all the functions in a unicellular organism.
(D) The size and shape of cells is uniform in multicellular organism.
Ans: C

Ques 2: Choose the correct option:
(ii) In human beings, after fertilization; the structure which gets embedded in the wall of uterus is-

(A) ovum
(B) embryo
(C) fetus
(D) zygote
Ans: B

Ques 3: Choose the correct option:
(iii) Reproductive age in women starts when

(A) menstruation starts
(B) breasts start developing
(C) body weight increase      
(D) all of these
Ans: A

Ques 4: Choose the correct option:
(iv) During dry weather while combing hair, sometimes we experience hair flying apart. The force responsible for this is:
(A) force of gravity
(B) electrostatic force
(C) force of friction
(D) magnetic force.
Ans: B

Ques 5: Choose the correct option:
(v) A toy car released with the same initial speed will travel farthest on

(A) muddy surface
(B) polished marble surface
(C) cemented surface
(D) glass block
Ans: B

Ques 6: Choose the correct option:
(vi) Loudness of sound is measured in units of:

(A) decibel (dB)  
(B) hertz (Hz)
(C) metre (m)
(D) metre/second (m/s)
Ans: A

Ques 7: Choose the correct option:
(vii) The movement of the earth?s plates causes

(A) cyclones
(B) lightning
(C) earthquakes
(D) thunderstorms
Ans: C

Ques 8: Choose the correct option:
(viii) We can see a non-luminous object, when light is

(A) emitted by the object falls on the eye.
(B) reflected from the object towards our eye
(C) completely passes through the object
(D) gets completely absorbed by the object
Ans: B

Ques 9: Choose the correct option:
(ix) Morning star is the name given to:

(A) Pole Star
(B) Star Sirius
(C) Planet Jupiter
(D) Planet Venus
Ans: D

Ques 10: Choose the correct option:
(x) The phenomenon of marble cancer is due to

(A) soot particles
(B) CFCs
(C) fog
(D) acid rain
Ans: D

Ques 11: (i) In what situation does the net force become zero? 
Ans: (i) When two equal forces act in opposite directions, the net force becomes zero.

Ques 12: (ii) What is a tester?
Ans: (ii) The device which is used to check current is called tester.  

Ques 13: (iii) Who discovered the static electricity or lightning in clouds? 
Ans: (iii) Benjamin Franklin in 1752.

Ques 14: (iv) How many kinds of nerve cells are there in retina?  
Ans: (iv) There are two kinds of cells:
Cones: Sensitive to bright light.
Rods: Sensitive to dim light.

Ques 15: (v) Name the brightest planet in the night sky.  
Ans: (v) Venus

Ques 16: (vi) What are multiple images? 
Ans: (vi) Images formed by mirrors placed at an angle to one another are called multiple images.

Ques 17: (i) Name the practice followed for large scale rearing of farm animals. 

(ii) What facilities are provided to farm animals?
Ans: (i) The practice of rearing of farm animals on a large scale is called animal husbandry.
(ii) In animal husbandry, animals are provided with proper food, shelter and care.

Ques 18: What do you mean by symbiotic relationship?
Ans: The relationship between two organisms in which both the organisms are benefited is called symbiotic relationship.

Ques 19: What is 4R principle?
Ans: The 4R principle means Reduce, Reuse, Recycle and Recover. One should develop these habits, which are environment friendly.  

Ques 20: Sodium metal is kept in kerosene but not in water. Why?
Ans: Sodium metal is highly reactive metal, when exposed in air, it starts to burn to form oxide. In the same way, it forms hydroxide with water. It does not react with kerosene. So, to prevent it, it is kept in kerosene, not in water.

Ques 21: Which zone of a flame does a goldsmith use for melting gold and silver and why? 
Ans: The blue, non-luminous zone (outer zone) because this point of the flame has the highest temperature, so it is used for melting gold and silver.

Ques 22: Crackers on ignition produce sound. Why?
Ans: When a cracker is ignited, a sudden reaction takes place with the evolution of heat, light, sound and a large amount of gas is liberated. Such a reaction is called explosion. So, cracker on ignition produces sound because of sudden formation of large amount of gas due to chemical reaction.

Ques 23: Explain why chloroplasts are found only in plant cells?
Ans: Green coloured plastids are called chloroplasts. They provide green colour to the leaves and chlorophyll in the chloroplasts of leaves is essential for photosynthesis. In human cell, it is not required. So, chloroplasts are found only in plant cells.

Ques 24: Mitochondria are important organelles of cell, often called 'powerhouse' of the cell. Give reason.
Ans: Mitochondria are called the ?powerhouse? of the cell because they provide energy for all the activities of the cell by oxidizing food in the form of ATP (Adenosine triphosphate).

Ques 25: Write difference between internal fertilization and external fertilization.
Ans: Difference between Internal fertilization and External fertilization:

Internal fertilization
External fertilization
Fertilization in which the fusion of the male and female gametes takes place inside the female body is called internal fertilization. e.g., Human, Cats, Dogs,
Fertilization in which the fusion of a male and a female gamete takes place outside the body of the female is called external fertilization. e.g., fish, star fish etc.

Ques 26: Write a short note on-
Adam’s apple
Ans: Adam's Apple: At puberty, the voice box or the larynx begins to grow. Boys develop larger voice boxes. The growing voice box in boys can be seen as a protruding part of the throat called Adam's apple.

Ques 27: What do you mean by vacuum? What happens to the loudness of sound in vacuum?
Ans: When air is removed completely from a vessel, it is said that there is a vacuum. The decreasing amount of air decreases loudness of sound. If all air is sucked from the vessel, the sound would stop completely. The sound cannot travel through a vacuum.

Ques 28: It is safer to use a wireless telephone rather than using a landline telephone during lightning. Explain the statement with the help of a reason. 
Ans: Since, lightning is an electrical discharge, so, during lightning, atmospheric electric charge may discharge through landline telephone wires which can become more dangerous. Thus, it is safer to use a wireless telephone rather than using a landline telephone during lightning.  

Ques 29: The bulb glows when the electric current passes through it. Explain why? 
Ans: Due to the heating effect of current, the filament of the bulb gets heated to high temperature and it starts glowing. However, if the current through a circuit is weak, the filament does not get heated sufficiently and even does not glow.

Ques 30: Differentiate between Fertilizer and Manure.
Ans: Differences between Fertilizer and Manure:

S. No.
A fertilizer is an inorganic salt.
Manure is a natural substance obtained by the decomposition of cattle dung, human waste and plant residues.
A fertilizer is prepared in factories.
Manure can be prepared in the fields.
A fertilizer does not provide any humus to the soil.
Manure provides a lot of humus to the soil.
Fertilizers are very rich in plant nutrients such as nitrogen, phosphorus and potassium.
Manure is relatively less rich in plant nutrients.

Ques 31: Complete the flowchart:
Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8
Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8

Ques 32: Friction is called a necessary evil. Why?
Ans: Friction is called a necessary evil because we cannot do anything without friction and it also shows effects. No movement would come to an end without friction. Nobody would rest without friction. We cannot write with pen or pencil if there is no friction. If an object starts moving, it would never stop if there was no friction. It is also necessary for grip and bringing movements to rest.

Ques 33: Why is it very difficult to control forest fire?
Ans: During extreme heat in the hot summer days, at some places dry grass catches fire. It is because the heat is sufficient to attain ignition temperature of grass. From grass, it spreads to trees and very soon the whole forest is on fire. It is called forest fire, it is very difficult to control forest fire. As fire spreads at a very high speed and in a very large area, it is very difficult to control it.

Ques 34: Discuss the various ways to reduce the friction.
Ans: Friction may be reduced in the following ways:
(i) Polishing the surface: We polish the rubbing surfaces to reduce their unevenness and make them smooth.
(ii) Lubricating the surface: To reduce friction in order to increase efficiency, when oil, grease or graphite is applied between the moving parts of a machine, a thin layer is formed there and moving surfaces do not directly rub against each other. These substances are lubricants which reduce the friction.
(iii) Using wheels and ball bearings: By using wheels and ball bearing, we convert sliding friction into rolling friction. This reduces friction between the two contact surfaces and helps us to save energy, effort and time.
(iv) Streamlining: Objects are given special shapes, such as streamlined body to aeroplanes. Their bodies? shapes make them lose less energy in overcoming friction. Hence, all vehicles are designed to have shapes that reduce fluid friction.

Ques 35: An alarm bell is kept inside a vessel as shown in Fig. A person standing close to it can distinctly hear the sound of alarm. Now if the air inside the vessel is removed completely how will the loudness of alarm get affected for the same person?
Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8
Ans: Initially, the person is able to hear the sound coming from air and from water distinctly. But after sometime, when the air is completely removed from the bottle, the sound will pass through the water and then the glass and finally reach to the man. So, the man will not hear the sound which was coming through the air initially.

Ques 36: How is CO2 added to the atmosphere in excess?
Ans: CO2 is continuously being released because of human activities and on the other hand, forest area is decreasing. Plants utilize CO2 from the atmosphere for photosynthesis, thereby decreasing the excess of CO2 in the air. Deforestation leads to an increase in the amount of CO2 in the air, because the number of trees which consume CO2 becomes lesser. Human activity thus contributes to the accumulation of CO2 in the atmosphere.

Ques 37: Discuss various systems of irrigation. 
Ans: The supply of water to crops at different intervals is called irrigation.
Various systems of irrigation are:
(i) Traditional methods: The water available in wells, lakes and canals is lifted up by:
(a) Moat (Pulley system)
(b) Chain pump
(c) Dhekli and;
(d) Rehat (Lever system)
Pumps are commonly used for lifting water.
(ii) Modern methods:
(a) Sprinkler system: This system is more useful on uneven land and with sandy soil. The perpendicular pipes, having rotating nozzles on top, are jointed to the main pipeline at regular intervals. When water flows through main pipes, it gets sprinkled on the crop as if it is raining.
(b) Drip system: In this system, water falls drop by drop just at the position of the roots. It is the best technique for watering fruit plants, garden and trees.  

The document Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8 is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8

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Class 8 Science Sample Paper - 3 Notes | Study Science Class 8 - Class 8