ncert scince 8 class answer 1 chapter
Answers
Answer:
1. Select the correct word from the following list and fill in the blanks.
float, water, crop, nutrients, preparation
(a) The same kind of plants grown and cultivated on a large scale at a place is called _____________.
(b) The first step before growing crops is _____________ of the soil.
(c) Damaged seeds would _____________ on top of water.
(d) For growing a crop, sufficient sunlight and _____________ and _____________ from the soil are essential.
Soln:
(a) The same kind of plants grown and cultivated on a large scale at a place is called the crop.
(b) The first step before growing crops is the preparation of the soil.
(c) Damaged seeds would float on top of the water.
(d) For growing a crop, sufficient sunlight and water and nutrients from the soil are essential.
2. Match items in column A with those in column B.
A B
(i) Kharif crops (a) Food for cattle
(ii) Rabi crops (b) Urea and superphosphate
(iii) Chemical fertilisers (c) Animal excreta, cow dung urine and plant wastes
(iv) Organic manure (d) Wheat, gram, pea
(e) Paddy and maize
sol:-
(i) Kharif crops. (e) Paddy and maize.
(ii) Rabi crops. (d) Wheat, gram, pea.
(iii) Chemical fertilisers. (b) Urea and superphosphate.
(iv) Organic manure. (c) Animal excreta, cow dung urine and plant wastes.
3. Give two examples of each.
(a) Kharif crop
(b) Rabi crop
Soln:
Kharif crops- Paddy and maize
Rabi crops- Wheat and Pea
4. Write a paragraph in your own words on each of the following.
(a) Preparation of soil
(b) Sowing
(c) Weeding
(d) Threshing
Soln:
a) Preparation of the soil is the first step in agriculture. Preparation of the soil is done to loosen the soil, which is essential for the root penetration into the soil. This allows the roots to breathe easily. Loosening of the soil allows the growth of earthworms and microorganisms, which will help to keep the soil fertile by adding humus to the soil. Loosening of soil also brings nutrient-rich soil to the top layer, which is essential for the growth of plants.
b) Sowing is an important process in crop production. First, healthy seeds are selected before sowing. After selecting healthy seeds sowing is done by either traditional methods or by using equipment’s seed drill.
c) Removal of unnecessary plants from the field is called weeding. Weeds compete with crop plants for nutrients and water. This will reduce the yield of the desired crops. Weeds also interfere while harvesting and gets mixed with crops. Some weeds are poisonous to animals and humans. Tilling is a common method which helps removal of weeds before sowing crops, manual methods like physical removal of plants are used to remove weeds. Weedicides are sprayed to get rid of weeds, but this method may affect the health of farmers because of chemicals used as weedicides.
d) Process of separating the chaff from the crop is known as threshing. Threshing is carried by a machine called ‘combine’ which is a harvester as well as a thresher. Threshing is also done by winnowing where to blow of wind is used to separate the chaff from crops.
5. Explain how fertilisers are different from manure.
Soln:
Fertilizers Manure
Fertilizer is an inorganic substance. Manure is an organic substance.
Fertilizers are prepared artificially. Manure is obtained by decomposition of animal, plant and human waste.
Prepared in factories. Prepared in fields.
Does not provide Humus to the soil. Provide humus to the soil.
Rich in plant nutrients. Relatively less plant nutrients.
Long term usage has adverse effects on soil. Long term usage improves soil fertility.