A. Answer these questions
1. What are agriculture?
Answer : Agriculture is the science that deals with crop production for human use
2. Name two plantation crops?
Answer : Rubber and coffee are examples of plantation crops.
3. Mention the major activities involved in growing a crop
Answer : Following activities are involved in growing a crop: (a) Ploughing (b) Levelling (c) Manuring
4. What are weeds?
Answer: Weeds are unwanted plants that grow along with the crops and compete with the crops for water, minerals and sunlight.
5. Mention three way of removing weeds from crop field.
Answer: Following ways are used to remove weeds: (a) Manually (b) By using tools like trowel, hoe or rake (c) Spraying weedicides
6. What are pets?
Answer: Pests are the organisms that attack the crops and damage them. Examples: Rodents or insects
7. Why are animal proteins are considered to be better than plant proteins?
Answer: Animal proteins are better than plant proteins because they contain certain essential amino acids that plant proteins lack. Also, animal proteins can be more easily digested by us.
8. When are kharif crops are shown?
Answer: Kharif crops are sown during the monsoon (from June to September).
9. What is animal husbandry?
Answer: Animal husbandry is the practice of rearing of animals for food and other purposes
10. What are the two things that we have to controlled in a cold storage?
Answer: Temperature and humidity are the two things that have to be controlled in a cold storage.
B. Answer these questions
1. (a) Why crop rotation is considered as good agriculture practice? (b) Why are pulses are alternated with crops like wheat or paddy?
(a) Crop rotation is a good agricultural practice because it maintains the nutrition of the soil. In this method, different crops are grown in succession in the same field.
(b) Pulses are alternated with crops like wheat or paddy because these crops consume lot of nitrogen from the soil. The roots of pulses form an association with nitrogen fixing bacteria and convert the atmospheric nitrogen into ammonia, which is used by plants. When the plants die, large amount of nitrogen fixed by them remains in the soil and becomes available for the next crop.
2. (a) What are green manure? (b) How is compost prepared?
(a) Green manure refers to the plants that are grown to produce manure. Examples of green manure include black gram, cluster bean and cowpea.
(b) Compost is formed when manure is produced in the presence of microorganisms that act on the waste matter covered in pits or in open. Waste that is decomposed by microorganisms includes crop residue, animal dung and sludge.
3. (a) What do you understands by biological control of weeds and pests? (b) In what way is biological control is better than the use of weedicides and pesticides?
Answer: (a) Biological control of weeds and pests refers to a method in which biological enemies of the weeds and pests like fungi, bacteria and insect are introduced in the field. This organism kills the weeds and pests by feeding upon or causing diseases. The other way of biological control is to develop disease resistant varieties of crops.
(b) Biological control is better than the use of weedicides and pesticides as it does not damage crops. it has no environmental impact. It is also less expensive than chemical control.
4. What are root nodules? How they are helpful?
Answer: Root nodules are the swellings that are found in the roots of leguminous plants. These nodules are formed by nitrogen fixing bacteria that live in leguminous roots.
Root nodules help in converting atmospheric nitrogen into ammonia that is used by plants to make protein. This process is known as nitrogen fixation.
5. What is surface irrigation? Mention two mode of irrigation under this catogary?
Answer: Surface irrigation refers to the different ways of irrigation in which water is allowed to run over the field.
There are two ways of surface irrigation:
(a) Furrow irrigation: Here, crop is planted on ridges and water is allowed to run through furrows between the ridges.
(b) Basin irrigation: Here, water is contained in the whole field by making bunds all around it
C. Answer these questions
1. Write briefly about the advantages and disadvantages of using chemical fertilizers?
Answer: Advantages of using chemical fertilisers:
(a) They provide specific nutrients that are not present in the soil.
(b) They are easy to store and transport as they are compact.
(c) They are water soluble; therefore, they are readily absorbed by plants.
Disadvantages of using chemical fertilisers:
(a) They make the soil more prone to erosion as they do not provide humus.
(b) They can harm soil fertility by making it more acidic or alkaline.
(c) They may cause eutrophication by mixing in water bodies.
2. What is nitrogen cycle?
Answer: Nitrogen cycle: The continuous circulation of nitrogen between plants and atmosphere is called Nitrogen cycle.
Nitrogen present in the air is converted into ammonia or other compounds of nitrogen that can be used by the plants through certain nitrogen fixing bacteria present in the soil . This is called nitrogen fixation. These compounds are used by plants to make proteins from where they pass on to the animals, who consume these plants.
When plants and animals die, the nitrogen compounds present in their bodies are converted into ammonia by microorganisms. This process is called ammonification.
The ammonia is ultimately converted into nitrites and a nitrate by bacteria is called nitrification. Nitrogen is returned to the atmosphere by the bacteria that break down nitrogen compounds to get energy and release nitrogen. This process id called de nitrification.
3. Write briefly about sources of irrigation in India?
Answer: Sources of irrigation in India:
(a) Dams: Dams are constructed across rivers. Water is carried through them by canals to different parts that are deprived of water. Permanent and inundation canals are used to carry water to different fields.
(b) Wells: They are used to tap groundwater. Electrical tube wells are now used to pump water from these wells for irrigation.
(c) Groundwater: Over 50 per cent of water used in irrigation is groundwater. In many parts of north India, groundwater is used as an additional source of irrigation.
1. The practice of growing fruit, vegetables, flowers and ornamental plants are horticulture.
2. The process of using the vapours of a chemical to disinfect a place and get rid of pests is called fumigation.
3. A buffer stock of grains is maintained to provide food during emergencies.
4. A mutually beneficial association between two organisms is called symbiosis.
5. Seeds have to be sown at the right depth and with adequate spaces in between.
6. Biological control is a method of controlling weeds or pests by using their natural enemies.
7. A fallow field is one that is left uncultivated for one or more seasons.
E. 1. (c) Winnowing 2. (d) can harvest, thresh and winnow 3. (a) 4. (b) nitrogen fixation
5. (a) drip irrigation 6. (d) between 0°C and 4°C 7. (a) Rice
F. 1. (a) pea
Roots of peas contain nodules with nitrogenfixing bacteria.
2. (d) jute
Jute is not a rabi crop
3. (a) and (c)
Jowar and bajra are millets that require very little water.
4. (b) winnowing
Winnowing is done after the crops are gathered.
5. (c) cowpea
Cowpea is an example of green manure.
For more rest of lessons visit: Basic Science for class 8