Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev

Science Class 8

Class 8 : Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev

The document Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev is a part of the Class 8 Course Science Class 8.
All you need of Class 8 at this link: Class 8

Class - VIII
Science Theory
TIME: 3 Hrs.
M.M: 80

General Instructions:
1. Attempt all the questions and follow the instructions given in each question.
2. Q.No. 1 is MCQs type; choose the correct option.
3. Q.No. 2 are Very Short Answer Type Questions, carry one mark each.
4. Q.No. 3 to Q.No. 9 are Short Answer Type Questions-I, carry 2 marks each.
5. Q.No. 10 to Q.No 19 are also Short Answer Type Questions-II, carry 3 marks each.
6. Q.No. 20 to Q.No 23 are Long Answer Type Questions, carry 5 marks each.

Q.1. Choose the correct options :
(i) Sulphurous acid turns blue litmus paper into :

(a) Blue
(b) Red
(c) Neutral
(d) No reaction
Ans:

(ii) Petroleum was formed from organisms :
(a) Living on the land
(b) Living in the sea
(c) Living on the plants
(d) Living on the rocks
Ans: b

(iii) In villages, people use wood as fuel because
(a)
it is considered to be an ideal fuel.
(b) of its easy availability and low cost.
(c) it is environment friendly.
(d) it catches fire easily.
Ans:  b

(iv) What do blackbuck, elephant, python, and golden cat together represent in a forest?
(a)
fauna
(b) ecosystem
(c) flora
(d) species
Ans:  a

(v) Which one of the following terms is not a part of the nucleus?
(a)
ribosomes
(b) chromosomes
(c) nucleolus
(d) cytoplasm
Ans: a

(vi) Reproduction by budding takes place in
(a)
hydra
(b) amoeba
(c) paramecium
(d) bacteria
Ans:  a

(vii) For the metamorphosis of tadpoles, which of the following elements must be available in water?
(a)
Chlorine
(b) Carbon
(c) Sulphur
(d) Iodine
Ans:  d

(viii) Which one of the following forces is a contact force?
(a) 
force of gravity
(b) force of friction
(c) magnetic force
(d) electrostatic force
Ans:  b

(ix) To sharpen the blade of a knife by rubbing it against a surface, which of the following will be most suitable?
(a)
Stone
(b) Plastic block
(c) Wooden block
(d) Glass block
Ans:  c

(x) An electric current can produce
(a)
heating effect only
(b) chemical effect only
(c) magnetic effect
(d) chemical, heating and magnetic effect
Ans: d

Q.2. (i) What is Teflon?
Ans:
Teflon is a special plastic on which oil and water do not stick. It is used for non-stick coating in cooking wares.
(ii) Why is phosphorus stored in the water?
Ans:
Phosphorus is a very reactive non-metal. It catches fire if exposed to air. So, it is stored in water to prevent it from in contact with atmospheric oxygen.
(iii) Name the slow process, which involves converting dead vegetation into coal.
Ans: 
Carbonization
(iv) How can we say that fish exhibits external fertilisation?
Ans: 
Female fish lay eggs in the water while male fish release their sperms in water. Sperms swim and reach the egg of fish randomly due to water currents, and thus external fertilisation occurs.
(v) What are the interactions of poles of two magnets?
Ans: 
(a) Like poles repel each other.
(b) Unlike poles attract each other.
(vi) Astronauts in outer space have to use radios to communicate with one another. Why?
Ans: There
 are no gases to help transmit sound in outer space. To communicate with one other, astronauts use electromagnetic waves such as radio waves, which can travel through a vacuum.

Q.3. What are petrochemicals?
Ans:
All synthetic fibres are prepared by several processes using raw materials of petroleum origin, called petrochemicals.

Q.4. Give reason :
Iron nails are placed in a copper sulphate solution. Write the word equation of the reaction involved.
Ans: When iron nails are placed in copper sulphate solution, displacement reaction occurs in which iron displaces copper as iron is more reactive than copper.
Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev

Q.5. It is difficult to burn a heap of green leaves, but dry leaves catch fire easily. Explain.
Ans:
As dry leaves have low ignition temperature than heap green leaves, green leaves have water and other elements. To ignite the green leaves, we have to heat them to their constituents' ignition temperature, which is comparatively high. So, it is easier to ignite dry leaves than green leaves.

Q.6. What do you understand by fuel efficiency?
Ans: Its calorific value determines fuel efficiency
: the amount of heat energy produced on 1 kg of fuel's complete combustion. The calorific value of a fuel is expressed in kJ/kg.

Q.7. What is an ecosystem?
Ans:
An ecosystem constitutes the plants, animals and micro-organisms in an area along with non-living components such as climate, soil, river deltas etc.

Q.8. What do you understand by Endemic species? Name two endemic flora and fauna.
Ans:
Endemic species are those species of plants and animals found exclusively in a particular area. A particular type of animal or plant may be endemic to a zone, a state or a country, e.g., Sal and wild mango are endemic flora, Bison and the Indian giant squirrel are endemic fauna of the Pachmarhi Biosphere Reserve.

Q.9. An astronaut travels from the earth to the moon. How do its weight and mass change?
Ans:
Mass of an object remains constant at all places, so the astronaut's mass will not change. The weight of an object depends upon gravity, and on the moon, gravity is lesser than the earth, so the weight of an astronaut will decrease.

Q.10. What is IVF?
Ans:
IVF or In-vitro fertilisation. In such cases, the doctor collects freshly released egg and sperms and keep them together for a few hours for fertilisation. When fertilisation occurs, the zygote is formed and allowed to develop for about a week and then it is placed in the mother’s uterus. Babies produced by this technique is called test-tube babies.

Q.11. Define Tissue.
Ans:
A tissue is a group of similar cells performing a specific function. Tissues together make an organ.

Q.12. When the cutting edge of a knife is put against a fast rotating stone to sharpen it, sparks are seen to fly. Explain the reason.
Ans:
Due to the friction between knife and stone, the knife's temperature and hence stone increases, and it increases to such a level that the sparks are produced which can be seen while sharpening it.

Q.13. Give reason :
Water is not used to control the fire involving electrical appliances or equipment.
Ans: In case of fire produced by an electric short circuit or electric equipment, water is not used because water is a good conductor of electricity and may result in electrocution or electric shock.

Q.14. What is the importance of using manure and fertilizers as an agricultural practice?
Ans: 
Using manure and fertilizers as an agriculture practice is important as crops' continuous growth makes the soil poorer in certain nutrients. These both are added to the soil in the form of nutrients for plants' healthy growth. Manure replenishes the soil with nutrients and also improves water retaining capacity, whereas fertilizers make the soil rich in a particular nutrient. They also help farmers to get a better yield of crops.

Q.15. Mention three examples that show that friction produces heat.
Ans:
Following examples show that friction produces heat :
(i) Warming of our palms when we rub them.
(ii) Rubbing sticks together to produce fire.
(iii) Warming of a machine's parts when it is operated.

Q.16. How does housefly make us sick?
Ans:
Housefly is a carrier of disease-causing microbes. The flies sit in the garbage and animal excreta. Pathogens stick to their bodies. When these flies sit on uncovered food, they may transfer these pathogens; whoever eats this contaminated food is likely to get sick.

Q.17. What are three main factors essential to maintain reproductive health? Explain their importance.
Ans:
Three main factors essential to maintain reproductive health are : (i) Balanced Diet: The diet which contains the correct amount of each constituent (such as carbohydrates, fats, proteins, vitamins, minerals) sufficient for normal growth and development of a body.
(ii) Personal hygiene: Adolescent boys and girls should take a bath regularly because the increased activity of sweat and oil glands can cause bacterial infection if not washed and cleaned every day.
(iii) Physical exercise for adolescence: Adolescent girls and boys should regularly exercise as they improve mental health, protect the person from any disease or fatigue, and increase the person's efficiency.

Q.18. Write three important uses of non-metals.
Ans:
Important uses of non-metals :
(i) Non-metals are essential for our lives as all living beings inhale oxygen and breathe out carbon dioxide during breathing.
(ii) They are used in fertilizers to enhance plants' growth.
(iii) Non-metal is used in the purple coloured solution that is applied to wounds as an antiseptic.
(iv) Non-metals are used in crackers.

Q.19. What are the chemical effects of electric current? Explain with the help of an example.
Ans:
 The following experiment can explain the chemical effects of electric current:
(i) Take two carbon rods with metal caps. Clean their metal caps.
(ii) Wrap copper wires around the carbon rods' metal caps and join them to a battery.
(iii) Pour a full cup of water into a glass bowl and add a salt teaspoon.
(iv) Immerse the electrodes in solution, but metal caps should be out of the water.
(v) Wait for 5 min.
(vi) Observe the electrodes.
(vii) The passage of electric current through a conducting solution causes a chemical reaction. As a result, bubbles of gas are formed near the electrodes. Deposits of metal may be seen on electrodes. Change of colour of the solution may occur. These are some of the chemical effects of the electric current.
Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev
Passing current through water

Q.20. How does air get polluted? Explain.
Ans:
 Air gets polluted for many reasons. A few of them are as follows :
(i) Vehicles produce high level of pollutants like carbon monoxide, carbon dioxide, nitrogen oxide, smoke etc. These are very poisonous gases. The burning of fuel from vehicles also produces pollution.
(ii) Many industries are also responsible for causing air pollution. Petroleum refineries release polluted gases such as sulphur dioxide, nitrogen dioxide etc. They cause respiratory problems, including lung damage.
(iii) Other kinds of pollutants are CFCs used in refrigerators, air conditioners and aerosol sprays, which deplete the ozone layer. It protects us from the ultraviolet rays of the Sun.
(iv) Some human activities like a forest fire, burning of firewood, cow dung cakes, burning of chaff etc., cause air pollution.
(v) Some natural phenomenon like fast dust storms, volcanic eruption produces smoke and dust particles. 

Q.21. What are food preservatives? Explain some common food preservatives.
Ans:
The chemical substances used to check or stop the growth of harmful micro-organisms in food are called food preservatives. These food preservatives keep the edible food materials protected from the invasion of micro-organisms, spoiling the food.
Some common food preservatives are :
(i) Salt: Common salt is used to preserve meat, fish, amla, raw mangoes, tamarind, etc.
(ii) Sugar: Jams, jellies and squashes are preserved by sugar. Sugar reduces the moisture content, which inhibits bacteria's growth, which can spoil food.
(iii) Oil: Edible oils are used as preservatives in vegetables and pickles. Oil does not allow moisture to surface, thus preventing harmful bacteria's growth.
(iv) Vinegar: It is used to preserve fruits, vegetables, fish, meat and pickles.

Q.22. What are the contact and non-contact forces? Explain briefly with suitable examples.
Ans:
Forces can be of two types :
(i) Contact forces.
(ii) Non-contact forces.
(i) Contact forces: The forces that come into play when two objects contact each other.
(a) Muscular force: The force exerted due to muscles' action is known as the muscular force. e.g., running, bending, walking etc.
(b) Frictional force: The force responsible for changing the state of motion of an object. Equal and opposite forces are being exerted on an object when its surface comes in contact with another surface. e.g., a car or scooter comes to rest.
(ii) Non-contact forces: The forces exerted from a distance without establishing contact are called the non-contact forces.
(a) Magnetic force: Force exerted by a magnet on another magnet or magnetic substances like iron is called magnetic force. e.g., Car sticking to an electromagnet.
(b) Electrostatic force: Force exerted by a charged body on another charged body or uncharged body is called electrostatic force. e.g., If we rub a comb with hair and bring it near some small bits of paper, it attracts the bits of paper towards itself. This is an electrostatic force.
(c) Force of gravity: The earth pulls every object towards its centre. The force exerted by the earth is called the force of gravity.

Q.23. Observe the figure and answer the following questions :
Sample Question Paper (2020-21)- 3 Class 8 Notes | EduRev
(i) Name the micro-organism and the group to which it belongs.
(ii) Name the food items on which the organism grows.
(iii) Does it grow well in dry or in moist conditions?
(iv) Is it safe to eat infected bread?

Ans: (i) Micro-organism is bread mould (Rhizopus), and the group is Fungi.
(ii) Organism grows on moist and stale bread.
(iii) It grows well in moist conditions.
(iv) No, the fungus spoils the bread by producing poisonous substances (toxins).

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