Science – VIII (Answer Key)

II. Fill in the blanks.

1. Leveller 2. Rainy, October 3. Winter, April 4. Inorganic 5. Dairy
III. Write True or False. Rewrite the false statement correctly.
1. True
2. False. It is better to use organic manure than fertilisers.
3. False. The same crop should not be grown on the same piece of land year after year.
4. False. Water logging is harmful for plants.
5. False. Threshing is done only for grains.
IV. Match the agricultural implements given in Column A with their use given in Column B.
1. (iii) 2. (i) 3. (ii) 4. (iv)
B. Answers the following questions in brief.
1. The loosening and turning of a few inches of the top soil is known as ploughing.
2. Pest is an insect which attacks crops, livestock, etc.
3. The branch of agriculture that deals with the rearing of animals (livestock) is known as animal husbandry.
4. The method of separating the grains from the chaff is called winnowing.
5. It will be a Kharif crop.
6. Kharif: Maize, paddy, groundnut, cotton
Rabi: Mustard, pea, gram, wheat
7. October to March
8. The following are the agricultural practices carried out by farmers:
(a) Soil preparation (b) Selection and sowing of seeds
(c) Manuring and adding fertiliser (d) Irrigation
(e) Weeding (f) Harvesting
(g) Threshing, winnowing (h) Storage
9. Drip irrigation is a modern method of irrigation. It involves providing water drop by drop at the roots of the
plants, thus avoiding wastage of water. This system is practiced in regions where water availability is poor.
10. Sprinkler system is a modern method of irrigation. It is used in regions where the soil cannot retain water for
long or where sufficient water is not available. In this method, water is sprinkled on crops as if it is raining.
11. If seeds are grown in the same place, there will be competition between them for obtaining nutrition from
the soil. Thus, overcrowding of the seeds may result in the shortage of nutrients, air, sunlight, water, etc.
and can kill the seedlings.
12. Soil is loosened before sowing seeds so that loose soil can hold more water and air. It also helps in the
growth and movement of earthworms and microbes which make the soil rich in nutrients.
13. The seeds must be sown at a reasonable depth under the soil so that they get air, water and suitable
temperature to germinate. If they are sown too deep they may suffocate without air and if they are spread
on the soil, they may be eaten up by the birds.
14. Large scale storage of grains is done in silos and granaries to protect them from pests like rats and insects.
Grains are also stored in air-tight godowns and in proper bags for the purpose of transportation.
15. Accumulation of excess water in the crop fields results in a condition called water-logging. It reduces air
in the soil, thereby damaging the roots. Even soil organisms get killed if it persists for a long time. It also

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 Science – VIII (Answer Key)
increases the amount of salts in the soil and damages the soil fertility.
16. After ploughing, it is necessary to level the soil because of the following reasons:
(i) To break and crush the big chunks of soil.
(ii) To prevent it from being eroded by wind or water.
(iii) To bring uniformity to the field so that water and manure can be distributed evenly to all parts of the
field.
17. Seed transplanting increases the crop production. It helps the farmers select only the healthy seedlings for
the plants. It also enables the farmers to plant the seedlings at the right spacing so that the plants receive
sufficient water, nutrients and sunlight.
18. Kharif: Rice or Soybean
Rabi: Pea or (Pea/Soybean are legumes that will fix nitrogen with the help of Rhizobium)

19. (a) Seeds should be sown at a proper depth and distance from each other.
(b) Seed should be healthy, clean and free from diseases.
D. Answer the following questions in detail.
1. To maintain the fertility of the soil following natural methods are used:
(i) Field fallow: The land is left free or fallow for one or more seasons to naturally regain the nutrients. 
(ii) Mixed cropping: It is the practice of growing two or more crops simultaneously on the same piece of
field. For example, a cereal crop such as wheat is grown along with a leguminous crop such as pulse
(e.g., gram).
(iii) Crop rotation: It is the process of growing a crop in between two similar crops. For example, wheat
crops are planted during the month of November and harvested in March and April. Rice crops are
planted in June-July and harvested in October-November. Now in between these two seasons, the
land lies empty. Instead of leaving it as it is, the farmers plant a pulse crop at this time.
2. Crop rotation is used for replenishing the soil with nutrients. This can be done by growing different crops
alternately. For example, wheat crops are planted during the month of November and harvested in March
and April. Rice crops are planted in June-July and harvested in October-November. Now in between these
two seasons, instead of leaving the land empty, the farmers plant a pulse crop in this time. A pulse crop
does not take time as long as wheat or rice to grow. So, by the time the farmer has to plant the cereal
crops, the pulse is ready to be harvested. Pearl millet is often grown in rotation with groundnut, cotton and
sometimes in South India with rice.
Uses of crop rotation include: 
(a) It maintains the fertility of the soil.
(b) Gives better yield.
(c) Prevents crop diseases and pests.
3. Multiple cropping is the practice of growing two or more crops simultaneously on the same piece of land.
It is an insurance against crop failure because the crops are chosen in such a way that the products and
waste materials from one crop help in the growth of the other crop. For example, wheat is grown along
with a leguminous crop such as gram. The uptake of nitrogen from the soil by wheat is compensated by
the addition of nitrogen in the soil by the nitrogen-fixing bacteria like Rhizobium present in the legume.
4. In drip irrigation, water is dripped directly at the roots of the plants. Thus, water is saved. This system is
practiced in regions where water availability is less. However, it is very expensive. In sprinkler irrigation,
water is sprayed with the help of rotating nozzles at regular intervals. This method is used where the soil
cannot retain water for long. It is less expensive than drip irrigation.

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Science – VIII (Answer Key)
5. Besides the given tools,the other items required for raising a garden are seeds and seedling of vegetables,
plants from nursery, kitchen waste, manure, water, soil.
Steps for raising the garden:
(a) Kitchen waste will be collected and composted in a pit.
(b) A patch of land will be identified for the garden ,with adequate sunlight available.
(c) Soil will be dug up and levelled with the help of a spade.
(d) Select seeds/seedlings as per the season. Sowing of seeds/transplanting of seedlings will be done.
Seeds should be uniformly placed with adequate spacing.
(e) Water the plants regularly with a water-can.
(f) Compost will be applied.
(g) Weeds will be removed periodically with the help of khurpi.
D. Higher Order Thinking Skills (HOTS)
1. Earthworms are considered as farmer’s friends as they turn and loosen the soil. This allows the roots to
breathe properly. They turn the organic matter in the soil into humus.
2. It is recommended to wash fruits and raw vegetables before eating them to wash away harmful chemicals
such as insecticides and pesticides which were sprayed while growing them.
3. Nursery is a place where plants are grown for a short time so that they can be adapted for the climatic
conditions of the field.
4. Melons and pumpkins crack open while on the plant because of excessive accumulation of water due to
heavy rains or irrigation practices putting the fruit under a lot of pressure. In addition to water, heat can also
cause the melons and pumpkins to split open by building pressure within the fruit. This happens when it
gets too hot.
5. Soaking seeds before sowing is necessary as it allows seeds to germinate quickly and easily. Soaking the
seed will soften the outer layer of the seed and allow water and nutrients to penetrate the seed, making
germination easier and faster.
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Science – VIII (Answer Key)

Questions for Practice

A. Objective Type Questions
I. Multiple Choice Questions
Tick (3) the correct option.
1. (a) 2. (b) 3. (c) 4. (d) 5. (b) 6. (b)
II. Fill in the Blanks.
1. microorganisms 2. Virus 3. dysentery and malaria
4. increase 5. Lactobacillus 6. antibiotics
7. antibodies 8. Female Aedes 9. carriers
10. Sodium benzoate, sodium metabisulphite 11. Pasteurised
III. Write true or false. Rewrite the false statements correctly
1. True
2. False. Autotrophic bacteria synthesise their own food.
3. True
4. True
IV. Match the names of scientists given in Column A with the discovery made by them given in
Column B.
1. (iii) 2. (ii) 3. (iv) 4. (i)
V. Match the microorganisms given in Column A to the group of which they belong given in Column B.
1. (iv) 2. (iii) 3. (i) 4. (ii)
B. Answer the following questions in brief.
1. Acquired Immune Deficiency Syndrome.
2. Female Aedes mosquito is the carrier of dengue virus.
3. Algae are found in moist places such as crevices of rocks, barks of trees, ditches, lakes, ponds and stagnant
water.
4. Fungi are saprophytic in nature and some are even parasitic.
5. Pasteurisation is a preservation method in which milk is heated at 70°C for 15 seconds and is then at once
chilled and stored. This prevents the growth of microbes. 
6. Viruses are regarded as being on the borderline of living and non-living because outside a living host they
behave like non-living organisms but when they enter the body of any living organism they grow and
reproduce very fast.
7. (a) Preservatives (b) Rhizobium

(c) Carrier/vector (d) Antibiotics
8. Baking bread/manufacture of alcoholic drinks.
9. The following are the diseases caused by microorganisms in:
Plants: Citrus canker and rust of wheat.
Animals: Anthrax and foot and mouth disease.
10. (a) Algae are the main source of food for many animals.

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 Science – VIII (Answer Key)
(b) They are used as natural manures for plants.
11. The following are the different methods of food preservation: Dehydration and sun-drying, smoking,
heating, adding chemical preservatives, refrigeration, using oil and vinegar and using salt and sugar.
12. The bacterial cell found in the following different shapes:
(i) rod-shaped, which are called bacilli
(ii) spherical shaped, which are called cocci
(iii) comma-shaped, which are known as spirilla or vibrio. 
13. Fungi reproduce by budding and spore formation. Yeast reproduces by budding. The bread mould
reproduces by spore formation. The spores can remain alive during unfavourable conditions and on the
onset of favourable conditions they germinate to form new fungi.
14. Food poisoning is caused due to the consumption of food spoilt by microorganisms. At the onset of
favourable conditions, microbes start growing on the food substance and release toxic chemicals which
spoil the food. Intake of these chemicals is harmful for the body. 
15. Advantages of food preservation:
(i) Reducing food wastage.
(ii) Availability of food supply especially when out of season at every place.
(iii) Increasing the storage period of foodstuff.
(iv) Making up for dietary inadequacies.
16. (a) Cholera: By maintaining personal hygiene and good sanitation practices.
(b) Typhoid: Eating properly cooked food, drinking boiled water, getting vaccinated against the disease.
(c) Hepatitis A: Drinking boiled water and getting vaccinated against the disease.
17. The probable reason is that the chaat was contaminated by pathogenic microbes due to unhygienic
conditions near the shop or the utensil used for serving could have contaminated.
18. The 'unused kneaded flour', if left in warm conditions, gets infected by microbes which cause fermentation
and spoils the flour. The pooris would remain in relatively good condition because they were deep fried in
heated oil that kills microbes.
19. (a) Polio/Chickenpox/Influenza.
(b) Virus can reproduce only inside the cells of the host.
20. Vaccines contain dead or weakened microbes of a particular disease. When a vaccine is introduced into a
healthy body, the body fights and kills them by producing suitable antibodies. These antibodies remain in
the body and protect it when the microbe enters the body again.
21. Beans and peas are leguminous plants and have Rhizobium in their root nodules. These bacteria can fix
atmospheric nitrogen to enrich the soil with nitrogen and increase its fertility.
22. Though mosquitoes live on land, their larvae grow in water. If water stagnation is prevented the larvae
cannot survive.
C. Answer the following questions in detail .
1. (a) Microorganism like yeast is widely used in the large scale production of alcohol, wine by the process of
fermentation.
(b) In agriculture industry, they are used to increase the soil fertility by fixing atmospheric nitrogen with the
help of bacterium Rhizobium.
(c) They play an important role in the preparation of medicine by producing chemicals called as antibiotics
which kills or stops the growth of disease-causing microorganisms.

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Science – VIII (Answer Key)
(d) They are used in the baking industry and also in production of curd.
(e) They also play a significant role in cleaning environment and in biological treatment of sewage and
industrial effluents.
2. Fresh milk is boiled before consumption to kill the microorganisms in it. But packed milk is pasteurised and
does not contain any microorganisms. It can thus be consumed without boiling.
3. Raw vegetables and fruits get easily infected by microorganisms and get spoilt. They are kept in the
refrigerator as low temperature inhibits growth of microbes. Jams and pickles contain sugar and salt as
preservatives. They do not get infected by microbes easily.
D. Higher Order Thinking Skills (HOTS)
1. The yeast in the dough releases carbon dioxide by the process of fermentation. This gas causes the dough
to rise.
2. In summers the temperature is optimum for the multiplication of Lactobacillus bacteria than in winters.
Under these favorable conditions, the bacteria multiplies very fast and produces more lactic acid which
coagulates milk proteins and converts milk into curd.
3. Warm milk provides favorable condition for the growth of bacteria than hot or cold milk which hinders the
growth of bacteria required for formation of curd.
4. Nitrogen being an inert gas does not itself react with the food and thus prevents oxidation. Potato chips
when sealed with nitrogen gas can be prevented from becoming rancid that can change the taste and
smell of chips. 
5. Our hands are the carriers of many microbial infectious diseases that may spread into our body while eating.
To keep ourselves protected from these diseases we must wash our hands before eating.
6. Rainy season and stagnant water leads to the growth of larvae of mosquitoes that may cause water-borne
diseases like malaria, typhoid and cholera, so it is necessary to empty water coolers frequently during the
rainy season.

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