NCERT Class 7 Science Ninth Chapter Soil Exercise Solutions

Inside Questions with Answers:

Why it is needed to ban the polythene bags and plastics?

Ans. Polythene bags and plastics pollute 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.

What is called humus?

Ans. The rotting dead matter in the soil is called humus.

What is called weathering?

Ans. soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering.

Define soil profile.

Ans. A vertical section through different layers of the soil is called the soil profile.

Define topsoil or the A-horizon.

Ans. Soil fertile and provides nutrients to growing plants. This layer is generally soft, porous and can retain more water. It is called the topsoil or the A-horizon.

What is called soil?

Ans. The mixture of rock particles and humus is called the soil.

Define sandy soil.

Ans. The soil is classified on the basis of the proportion of particles of various sizes. If soil contains greater proportion of big particles it is called sandy soil.

Define clayey soil.

Ans. If the proportion of fine particles is relatively higher, then it is called clayey soil.

What is called Loamy soil?

Ans. Loamy soil is a mixture of sand, clay and another type of soil particle known as silt.

**Percolation rate (mL/min) = amount of water (mL) / percolation time (min)

What is called erosion?

Ans. The removal of land surface by water, wind or ice is known as erosion.

Exercise Questions with Answers:

Tick the most suitable answer in questions 1 and 2.

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

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

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.

Column I	Column II
(i) A home for living organisms	(b) All kinds of soil
(ii) Upper layer of the soil	(c) Dark in colour
(iii) Sandy soil	(a) Large particles
(iv) Middle layer of the soil	(e) Lesser amount of humus
(v) Clayey soil	(d) Small particles and packed tight

4. Explain how soil is formed.

Ans. soil is formed by the breaking down of rocks by the action of wind, water and climate. The nature of any soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it.

5. How is clayey soil useful for crops?

Ans. Crops such as wheat are grown in the fine clayey soils, because they are rich in humus and are very fertile.

6. List the differences between clayey soil and sandy soil.

Ans. I.  The proportion of particles of various sizes. If soil contains greater proportion of big particles it is called sandy soil. Whereas,

If the proportion of fine particles is relatively higher, then it is called clayey soil.

1. Sand particles are quite large whereas Clay particles, being much smaller.

III. Water can drain quickly through the spaces between the sand particles.

Whereas,

water can be held in the tiny gaps between the particles of clay.

7. Sketch the cross section of soil and label the various layers.
   
8. Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.

Ans. We know, Percolation rate = amount of water (mL) / percolation time (min)

Here, amount of water = 200 mL.

percolation time = 40 min.

Therefore, Percolation rate = 200 mL / 40 min

= 5 mL/min.

9. Explain how soil pollution and soil erosion could be prevented.

Ans.

How Soil Pollution can be prevented:

Polythene bags and plastics pollute 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 a 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.

How soil erosion can be prevented:

Cutting of trees and deforestation should be prevented and effort should be made to increase the green areas.