NCERT CLASS 7 SCIENCE CHAPTER 9 SOIL
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NCERT CLASS 7 SCIENCE CHAPTER 9 SOIL
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NCERT CLASS 7 SCIENCE CHAPTER 9 SOIL
Question Answers
NCERT IN – TEXT QUESTIONS OF BOOJHO AND PAHELI
Q.1 I wonder why I found some pieces of plastic articles and polythene bags in the soil sample collected from the roadside and the garden. (page 97)
Ans. It is because throw used plastic things and polythene bags in the soil.
Q.2 I want to know whether the soil from a field can be used to make toys. (page 97)
Ans. Yes
Q.3 I want to know what kind of soil should be used for making matkas and surahis? (page 99)
Ans. Clayey soil.
Q.4 Boojho wondered why there was a difference in the absorption of water in the two squares? (Page 100)
Ans. Because different soils are used to make the two squares.
Q.5 What is the difference between rate of percolation and the amount of water retained ? (Page 104)
Ans. Rate of percolation is the amount of water percolated per unit Time through soil whereas the amount of water retained is the amount of water absorbed by the soil. Thus, rate of percolation and water retention are opposite attributes.
NCERT TEXTBOOK EXERCISE. (Pages 105-106)
Tick the most suitable answer in the questions 1 and 2.
Q.1 In addition to the rock particles, the soil contains :
(i) air and water
(ii) water and plants
(iii) minerals, organic matter , air and water
(iv) water , air and plants.
Ans.(iii) minerals, organic matter, air and water.
Q.2 The water holding capacity is the highest in :
(i) Sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam.
Ans. (ii) clayey soil.
Q.3 Match the items in Column I with those in Column II
| Column I | Column II |
| (i) A home for living organisms | (a) Large particles |
| (ii) Upper layer of the soil | (b) All kinds of soil |
| (iii) Sandy soil | (c) Dark in colour |
| (iv) Middle layer of the soil | (d) Small particles and packed tight |
| (v) clayey soil | (e) Lesser amount of humus. |
Ans. (i)(b); (ii)(c); (iii)(a); (iv)(e); (v)(d);
Q.4 Explain how soil is formed.
Ans. The soil is the matter which cover the top most layer of the earth in most of area it is one of the most important natural resources.
Long ago earth was a very hot sphere and then converted into a very hard and rocky land. These rocks were broken into smaller pieces by violent earthquakes. Volcanic eruptions also made the rocks and lava into smaller pieces. in cold temperatures the ice in the crevices of rocks expanded to break in it into smaller pieces and thus gradually the soil was formed. the nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.
Q.5 How is clayey soil useful for crops?
Ans. Clayey soil is good in retaining water. They are rich in humus and are very fertile. They also hold sufficient water due to the presence of smaller particles and certain enough air due to the presence of some large particles.
Q.6 List the differences between clayey soil and sandy soil.
Ans.
| Clayey Soil | Sandy soil |
| (i) They contains more than 50% of clay particles. | (i) They contains about 60% of sand particles. |
| (ii) Water holding capacity is very high. | (ii) Water holding capacity is very low. |
| (iii) Suitable for plant growth. | (iii) Not suitable for plant growth. |
| (iv) Low percolation rate. | (iv) High percolation rate. |
Q.7 Sketch the cross section of soil and label the various layers.
Ans.
Fig. A soil profile
Q.8 Razia conducted an experiment in the field related to the rate of percolation. She observe that it took 40 minute for 200 ml of water to calculate through the soil sample. Calculate the rate of percolation
Ans. We know that:
Rate of percolation = Amount of water(mL)/ Percolation time (min)
= 200/40
= 5 mL/min.
Thus, the rate of percolation is 5 mL/min.
Q.9 Explain how soil pollution and soil erosion could be prevented.
Ans. Polythene bags are plastics polluted the soil. They also kill the organisms living in the soil. That is why there is a demand to Ban the polythene bags and plastics.Other substances which pollute the soil are number of waste products, chemicals and pesticides. Waste products and chemicals should be treated before they are released into the soil. The use of pesticides should be minimised.
Soil erosion can be slowed down the soil can be conserved by regulating the factors responsible for it. Some method of prevent or slow down the soil erosion are:
(i)To stop the unnecessary cutting of forests and trees.
(ii)To stop the excessive use of grass land due to overgrazing by cattle.
(iii) Growing vegetation along the boundary of the fields and open grounds.
(iv) Making use of proper and scientific methods for cultivation such as crops rotation. This maintains the natural fertility of the soil and at the same time soil also maintains its capacity to hold water. Soil remains wet and cannot be easily carried away by water and blown up by wind.
(v) Making use of scientific methods for irrigation and water drainage.
(vi)Cutting the hill slopes into steps or terraces and adopting terrace cultivation on hills slopes.
Q.10 Solve the following crossword puzzle with the clues given :
Across :-
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organism in the soil.
Down :-
1. In desert soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Ans. Do yourself.
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