NCERT Solutions for Class 7 Science Chapter 9 Soil

NCERT Solutions for Class 7 Science Chapter 9 Soil are part of NCERT Solutions for Class 7 Science. Here we have given NCERT Solutions for Class 7 Science Chapter 9 Soil.

Board	CBSE
Textbook	NCERT
Class	Class 7
Subject	Science
Chapter	Chapter 9
Chapter Name	Soil
Number of Questions Solved	10
Category	NCERT Solutions

NCERT Solutions for Class 7 Science Chapter 9 Soil

Tick the most suitable answer in questions 1 and 2.
Question 1.
In addition to the rock particles, the soil contains

1. air and water
2. water and plants
3. minerals, organic matter, air and water
4. water, air and plants

Solution:
3. minerals, organic matter, air and water

Question 2.
The water holding capacity is highest in

1. sandy soil
2. clayey soil
3. loamy soil
4. a mixture of sand and loam

Solution:
2. clayey soil

Question 3.
Match the items in Column I with those in Column II:
Column I
(i) A home for living organisms
(ii) Upper layer of the soil
(iii) Sandy soil
(iv) Middle layer of the soil
(v) Clayey soil

Column II
(a) Large particles
(b) All kinds of soil
(c) Dark in colour
(d) Small particles and packed tight
(e) Lesser amount of humus

Solution:
(i)-(b)
(ii)-(c)
(iii)-(a)
(iv)-(e)
(v)-(d).

Question 4.
Explain how soil is formed.
Solution:
There are a number of natural processes involved in the formation of soil. Some of them are as follows :
(i) Earthquakes or volcanic eruptions: There is a hard layer of rocks just below the earth. Due to natural calamities like earthquakes or volcanic eruptions, these big and heavy rocks are broken into smaller pieces and come on the surface of the earth.

(ii) Weathering of rocks: Due to fast-blowing winds, snowfall, moving glaciers and running water from rains, fine particles from the surface of rocks are carried to different places. This process is very slow and takes thousands of years. This is called physical weathering.

(iii) Corrosion or decomposition: The smaller particles of rocks obtained due to weathering, get further decomposed when exposed to air and moisture for long. These processes range from oxidation, reduction, hydration, hydrolysis or carbonization. Lichens and other plants also help in this process. For example, rocks of minerals like felspar and mica combine with water through the process of hydration and become soft and easily disintegrable. Silicate rocks on hydrolysis produce silicate clays. These are also slow processes. These are also called chemical weathering.

(iv) Addition of humus: Finally, the decomposed parts of dead plants and animals get mixed up with the soil formed due to the processes mentioned above. This gives the soil enough energy in the form of organic matter.

Question 5.
How is clayey soil useful for crops?
Solution:
Clayey soil has the following features:

• It has a good water-retaining capacity.
• Rich in humus.
• Fertile in nature.

This is the reason why this soil is useful for growing crops like wheat and rice.

Question 6.
List the differences between clayey soil and sandy soil.
Solution:

S. No.	Sandy soil	Clayey soil
(i)	High percolation rate	Low percolation rate
(ii)	Low water retention capacity	High water retention capacity

Question 7.
Sketch the cross-section of soil and label the various layers.
Solution:

Question 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.
Solution:
It is given that,
Amount of percolated water = 200 ml
and time is taken for percolation = 40 min
We know that,
Rate of percolation (ml/min) = \(\frac { Amount\quad of\quad percolated\quad water\quad }{ Percolation\quad time } \)
= \(\frac { 200\quad mL }{ 40\quad min } \) = 5 mL/min.
Rate of percolation will be 5 ml/min.

Question 9.
Explain how soil pollution and soil erosion could be prevented.
Solution:
Prevention of soil pollution: Polythene bags that are made up of plastics, pollute the soil. Other substances which pollute the soil are a number of waste products, like chemicals and pesticides. So to prevent soil pollution:

1. There should be a ban on polythene bags and plastics.
2. Waste products and chemicals should be treated before they are released into the soil.
3. The use of pesticides should be minimized.

Prevention of soil erosion: Soil erosion can be prevented by:

1. planting of trees
2. protecting of forests
3. holding suitable minerals or organic matter in proper amounts.
4. maintaining the porous structure of the soil.
5. Control and reclamation of ravines and adopting shifting cultivation.

Question 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.
Solution:

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