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Question 1:

Large rocks break into smaller particles due to changes in temperature because
(a) they expand when heated and contract when cooled.
(b) hot water will dissolve things better than cold water.
(c) they absorb all the sun's energy.
(d) water contracts when it freezes.

Answer:

(a) they expand when heated and contract when cooled
    
  Large rocks expand during day when sunlight falls on them and contract when cooled at night.
Therefore, repeated expansion and contraction due to change in temperature leads to their breakage.

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Question 2:

Small particles of rock are changed into soil when they are
(a) made into fine powder
(b) mixed with humus
(c) mixed with water
(d) all of the same size

Answer:

(c) mixed with water

When small particles of rock are mixed with water, they change into soil through physical and chemical weathering processes.

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Question 3:

The roots of plants cannot get the oxygen they need when
(a) the soil is filled with water.
(b) there is humus in the soil.
(c) they grow too long.
(d) the soil is ploughed.

Answer:

(a) the soil is filled with water
When soil pores are filled with water, the roots of the plants cannot get the oxygen they need because the soil is said to be waterlogged.

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Question 4:

Soil bacteria are important because
(a) they use up the carbon dioxide in the soil.
(b) they hold water in the soil.
(c) they break down organic matter.
(d) they destroy harmful insects.

Answer:

(c) they break down organic matter
Soil bacteria are the decomposers that break down plant and animal remains.

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Question 5:

Loamy soil
(a) holds all the water that enters it.
(b) permits only a certain amount of water to enter it.
(c) allows water to trickle through it at a moderate pace.
(d) allows water to pass through it rapidly.

Answer:

(c) allows water to trickle through it at a moderate pace
Loamy soil consists of equal amount of fine and large particles that allow water to pass through at a moderate rate.

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Question 6:

When soil contains a good amount of clay
(a) water will pass through it easily.
(b) it will hold on to most of the water poured onto it.
(c) it will have many air spaces in it.
(d) it is ideal for growing rice.

Answer:

(d) it is ideal for growing rice

When soil contains a good amount of clay, it absorbs most of the poured water that is ideal for growing rice.

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Question 7:

Growing trees along the roadside will
(a) hold soil on the sides of the road.
(b) make travel along the roads safer.
(c) keep the temperature along the roads much higher.
(d) keep wildlife away from the roads.

Answer:

(a) hold soil on the sides of the road

Growing trees along the roadside will hold soil on the sides of the road.

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Question 8:

The substance in the form that makes it fertile and provides nutrients to the soil is _____________.
(a) Water
(b) air
(c) humus
(d) clay

Answer:

(c) humus

Humus comprises various organic matter or nutrients that are essential for plants to grow. Hence, it makes soil fertile and provides nutrients to the soil.

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Question 9:

On which of the following basis is soil classified?
(a) Shape of the particles present in the soil
(b) Size of the particles present in the soil
(c) The amount of water that soil can hold
(d) Amount of humus present in the soil

Answer:

(b) Size of the particles present in the soil.

Soil is classified by the size of its particles.

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Question 10:

How is soil formed?

Answer:

Soil is formed by a natural process known as weathering of rocks, where large pieces of rocks are broken down into smaller pieces.
Weathering occurs by following three means:
(i) Physical weathering: It occurs because of change in climatic factors such as temperature, wind, rain water, ice and snow.
(ii) Chemical weathering: It occurs through chemical processes such as hydrolysis, hydration, oxidation and reduction. The primary end products of chemical weathering are silica, clay, inorganic salts and hydrated oxides.
(iii) Biological weathering: It is carried out by living organisms such as lichens and bryophytes.

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Question 11:

 Explain the role of water in the formation of soil.

Answer:

Water plays an important role in both physical and chemical weathering of rocks to form soil.
In physical weathering, water seeps into the rocks, which expands on heating and contracts on cooling. This repeated contraction and expansion results in breaking of rocks.
In chemical weathering, water reacts with carbon dioxide to form weak acids. These acids react with rocks and change the chemical composition of rocks. Thus, the rock is separated into soluble and insoluble particles, i.e., rocks break down into smaller pieces.

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Question 12:

 Distinguish between physical and chemical weathering.

Answer:

Physical Weathering Chemical Weathering
It occurs because of climatic factors such as temperature, wind, rain water, ice and snow. It occurs through chemical processes such as hydrolysis, hydration, oxidation and reduction.
It is the class of processes that causes the disintegration of rocks without chemical change. It changes the composition of rocks, often transforming them when water interacts with minerals to create various chemical reactions.

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Question 13:

 Mention the importance of the following in the soil:
air, water, humus

Answer:

Soil has empty spaces between them called pores. These pores contain air, which is very important for plant's life. They are composed of oxygen, carbon dioxide and nitrogen that plants absorb through their roots.

Water acts as a carrier of mineral elements and oxygen for the proper growth of plants. Water from the soil enters the plant through tiny root hairs. Along water, plants get their required minerals.

Humus consists of decaying plant and animal remains. It performs various important functions for the growth of plants. It absorbs and holds water and contains rich nutrients that are essential for plant's growth.



Page No 128:

Question 14:

Describe an experiment to show the water-holding capacity of different types of soil.

Answer:



Take a funnel, filter paper, measuring flask (according to the number of soil types we compare) and kitchen weighing scale.
Place the filter paper in the funnel and place the funnel on the measuring flask. Weigh about 25 g of each sample of soil and place it in each measuring flask. Pour 50 ml of water in each funnel. Record the speed at which the water drains out through each funnel into the measuring flask.
To determine the water-holding capacity of different soil, subtract the amount of water in the measuring flask from the amount of the water taken, i.e., 50 ml. Higher the resultant value of volume of water in the funnel, larger is the water-holding capacity of soil.

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Question 15:

Write a short note on soil erosion including the following phrases:
afforestation, wind, deforestaton

Answer:

The loss of the fertile topsoil is known as soil erosion. The layer below the topsoil is called subsoil layer, and it is not suitable for growing plants. The major reasons  for soil erosion are heavy rainfall and strong winds.
In the case of ​deforestation—that is, cutting of large number of plants and trees over a wide range of area—the fertile layer of the topsoil is exposed and carried away by the water and the wind easily.
Afforestation—that is,  planting more number of trees—solves the problem of soil erosion by holding the fertile layer of soil by the roots of plants and trees tightly and thus cannot be washed away by strong winds or heavy rainfall.

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Question 16:

Look at the soil profile and write the following names in the correct places next to the arrows.
weathered parent material, surface layer, subsoil, topsoil
figure

Answer:

1  -  Surface layer
2  -  Topsoil
3  -  Subsoil
4  -  Weathered parent material

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Question 17:

Mark the following statements true or false. Rewrite them correctly.
(a) The parent material contains the remains of dead plants and animals.
(b) Plants take root in the surface layer.
(c) Parent material contains mostly rock particles.
(d) The subsoil contains large quantities of organic material.
(e) A thick layer of fertile topsoil helps plant growth.
(f) Plants use the water and minerals found in surface layer for growth.
(g) Bedrock containing large unweathered rock is found below the parent material.

Answer:

(a) False
      The parent material consists entirely of rock particles.

(b) False
      Plants take root in the topsoil.

(c) True

(d) False
      The subsoil contains less quantities of organic material as compared to the topsoil.

(e) True

(f) False
     Plants use the water and minerals found in the topsoil for growth.

(g) True

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Question 18:

Which are the best soil types for growing plants and why?

Answer:

Black soil is best suited for growing sugarcane and cotton because it is rich in iron and magnesium minerals; also, it can hold water.
Alluvial soil is best suited for growing wheat, rice and sugarcane because it is very fertile and rich in humus.
Desert soil is best suited for growing cacti, date palms and coconut palms because they does not need much water.
Laterite soil is best suited for the cultivation of coffee, tea, coconut and banana because it is rich in nutrients and is found in regions with good rainfall, which fulfils the need for good quantity of water.

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Question 19:

Rice fields need standing water for a good crop. Which kind of soil will be most suitable for planting rice-soil with a higher or lower rate of percolation? Why?
figure

Answer:

A soil with lower rate of percolation and higher capacity of water retention will be most suitable for planting rice because rice seeds attain the required nutrients from this paddy water. Also, this water helps to keep the weeds away from the field.

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Question 20:

What is the importance of humus in garden soil?

Answer:

Humus is a dark-coloured organic matter formed by the decomposition of plant and animal remains present in the soil. It holds the topsoil in place. It absorbs and holds the water useful for growing plants. It provides food for various plants and animals present in the soil. Humus is rich in minerals; hence, it provides optimum conditions for plant growth. Good humus count also reduces water and wind erosion of soil. Hence, it is important to add humus in garden soil.



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