CBSE NCERT | Class VII (7th) | Science | Chapter 9 : Soil | Exercises

CBSE NCERT | Class VII (7th) | Science | Chapter 9 : Soil | Exercises

Tick the most suitable answer in questions 1 and 2.
1. Question : 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
Answer : (iii) minerals, organic matter, air and water

2. Question : The water holding capacity is the highest in
(i) sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam
Answer : (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
Answer:

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.

Answer :How Soil is formed : weathering of rocks produces small particles of various materials. These include sand and clay. The relative amount of sand and clay depends upon the rock from which the particles were formed,and the local terrain. The mixture of rock particles, sand, clay and humus is called the soil. In addition to these, living organisms, such as bacteria, plant roots and earthworm are also important parts of any soil.

5. Question : How is clayey soil useful for crops?
Answer : Clayey soil is  useful for growing certain kind of crops  of cereals like wheat and grams, which requires excess of water. Clayey soil is good for retaining water. For the same reason clayey soil  with organic matters are good for Paddy.

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

Answer :                             Differences between clayey soil and sandy soil

Clayey Soil

Sandy Soil

1. The proportion of fine particles is relatively higher. 2. The clayey soil is less aerated as clay particles, being much smaller, pack tightly together, leaving little space for air 3. The clayey soil is heavy less air and more water content 4. It can retain good amount of water in the tiny gaps between the particles of clay 5. It is suitable for crops like Paddy, wheat and grams

1. The proportion of big particles is relatively higher 2. The sand is well aerated as due to large particle size, they can not fit tightly to gether and have large spaces filled with air in between the particles. 3. The sand is light in weight 4. The sand is almost dry as it can not retain water due to large particle size. 5. Sandy soil is suitable for pee nuts and sandy-loam is for cotton crops.

7. Sketch the cross section of soil and label the various layers.

==========    <----A-horizon - rich in humus and minerals, This layer is generally soft, porous and can retain more water.   <----B-horizon - lesser amount of humus but more of minerals, generally harder and more compact      <----C-horizon - made up of small lumps of rocks with cracks and crevices.   <----Bedrock - hard and difficult to dig with a spade  ==========

Sectional View of Soil Layers (Soil Profile)

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.

Answer :
As we know percolation rate of water is different in different types of soil. It is highest in the sandy soil and least in the clayey soil. The rate of Water percolation is given by the following formula :-

                                                amount of water (mL)             200 ml
Percolation rate (mL/min) = __________________    =     ______     =    5 ml / minute


                                                percolation time (min)            40 min

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

Soil Pollution : 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.

Soil Erosion : The removal of land surface by water, wind or ice is known as erosion. Plant roots firmly bind the soil. In the absence of plants, soil becomes loose. So it can be moved by wind and flowing water. Erosion of soil is more severe in areas of little or no surface vegetation, such as desert or bare lands. So, cutting of trees and deforestation should be prevented and effort should be made to increase the green areas.


10. Solve the following crossword puzzle with the clues given:

1
		2
		4		5								3
							6
				7

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.
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Extended Learning — Activities and Projects
1. Boojho would like to know the difference between raw and baked soil?
Investigate how the soil from which matkas are made is different from the soil used to make statues.

2. Paheli is worried. She could see a brick kiln from her house. Bricks were being made there. There was so much smoke coming out of the kiln. She was told that the best quality of clay is required for making
pottery, statues and bricks. She has seen truck loads of bricks being taken away for construction of buildings. At this rate, she fears, no soil will be left. Are her fears justified? Discuss this problem with your parents, teachers and other experts of your area and prepare a report.

3. Try to find out the moisture content of a soil sample. One method is given here.
Activity: Take 100g soil. (Take help from any shopkeepers to weigh the soil.) Place it on a newspaper in the sun and allow it to dry for two hours. This activity is best done in the afternoon. Take care that the
soil does not spill outside the newspaper. After drying it, weigh the soil again. The difference in the weight of the soil before and after drying gives you the amount of moisture contained in 100 g of soil. This is called the percentage moisture content.
Suppose your sample of soil loses 10 g on drying. Then
In this example
Per cent of moisture in
Per cent of moisture in soil = wt. of moisture (g)/Original wt. of soil sample (g)
 In this example

Per cent of moisture in soil =  10 X 100/ 100 = 10 %
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Did you know?

Rivers of north India, which flow from Himalayas, bring a variety of materials including silt, clay, sand and gravel. They deposit their materials called alluvial soil, in the planes of north India. This soil is very fertile and supports nearby half the population of India.