Soil is an important chapter in DAV Class 7 Science book. We have given solutions to DAV Class 7 Science chapter soil. We have also given examples and explanations in many questions so that the students understand the concepts well.
DAV Class 7 Science Chapter 10 Solutions
A. Fill in the blanks.
1. Various layers in the soil are called ___________.
2. The intermediate particles, that are neither very rough, nor too smooth, are termed as ___________.
3. ___________ is the tendency of similar particles to stick to one another.
4. Soil air is important for roots to carry out ___________.
5. ___________ and ___________ cause soil pollution.
Ans: (1) soil horizons
(2) silt
(3) Cohesion
(4) breathing
(5) Insecticides, fertilisers
B. Match the following:
Answer: 1. Clay
2. Humus
3. Earthworms
4. Well aerated
5. No percolation
C. Tick the correct option.
Answer:
1. organic acids
2. Bedrock
3. Earthworm
4. clayey soil
5. Sandy loam
D. Answer the following questions in brief.
Q. 1. State the meaning of the term ‘soil.
Answer: Soil can be called a mixture of organic matter, minerals, gases, liquids, and decayed organisms that together support life. It is formed by the weathering of rocks.
Q. 2. List the four main agents of physical weathering.
Answer: The four main agents of physical weathering of rocks are:
Temperature: Increase in temperature causes weathering
Wind: Wind can also cause weathering in rocks.
Plants: Plants can start growing on the rocks and when the plants grow further it can cause weathering of the rocks.
Water: Running water can cause slow weathering of the rocks.
Also Check: Weather, Climate and Adaptation of Animals Solutions
Q. 3. Write one difference between sand, clay and silt.
Sand: These mineral particles are the coarsest and largest
Clay: These are fine-grained in nature and contains clayey minerals.
Silt: It is dust-like sediment that is deposited by wind, ice and water. They are neither rough nor smooth.
Q. 4. Name the types of soil classified on the basis of soil texture.
Answer: On the basis of soil texture, the soil can be categorized into these 3 categories: Sandy soil, clayey soil & loamy soil.
Q. 5. Give the meaning of the term ‘Cohesion.
Answer: When the particles of a substance stick to each other the phenomenon is called cohesion. Example: the behaviour of water molecules.
Q. 6. List any three causes of soil pollution.
Answer 6: The 3 causes of soil pollution are as follows:
Acid rain has a bad impact on the fertility of the soil.
Waste disposal by humans. The accumulation of waste materials degrades the quality of the soil.
Industrial activities can cause soil pollution
E. Answer the following questions.
Q. 1. Classify, and explain, the categories of soil on the basis of ‘texture of the soil.
Answer: On the basis of soil texture, soil is classified into three categories- sandy soil, clayey soil and loamy soil.
(1) Sandy soils – Sandy soils have soil particles that are coarsest and bigger in size. The particles of this soil have sufficient space between them so they are well aerated. This soil is not suitable for growing various crops. This soil is good at draining the water quickly.
(2) Clayey soils – Clayey soils have a higher proportion of fine and smooth soil particles. Clayey soil is heavier in weight. The particles in the clayey soil are closely packed. It can be used for growing multiple crops. Clayey soil can not drain water fast.
(3) Loamy soil – Loamy soil is a mixture of sand, silt and clay particles. It can hold both air and water. Loamy soil has humus also. It is considered to be the best soil for growing most of the crops.
Also Check: DAV Class 7 Science Chapter 9 Solutions
Q. 2. Differentiate between infiltration rate and percolation rate.
Answer:
Infiltration Rate: This is the speed at which the water enters the soil.
Percolation rate can be called the time, expressed in minutes per inch, required for the water to seep into saturated soil at a constant speed.
Q. 3. Write a short note on ‘composition of soil.
The soil can be comprised of different components. The amount of component may depend on the parent rock and also the organic materials present in the given soil. Let us discuss the components of the soil one by one:
Organic material: Plants and animals that have decomposed are the main source of this component. It can be categorized into 3 types:
Completely decomposed
Partially decomposed
Non decomposed organic material
Water: Water is also one of the main components of the soil. the nutrients are dissolved in it and transported to different parts of the plant
Minerals: These are found in the soil and their composition may vary. These components are solid in nature.
Soil air: Spaces, between the soil particles, contain air. Well aerated soils are good for keeping the roots healthy. Nitrogen and oxygen gases are present in the pores. Nitrogen is fixed by the microbes by the process of nitrogen fixation.
Q. 4. “The type of crop that may be grown in a particular field depends on the type of soil: Give three examples in support of this statement.
Answer: Each type of crop requires different types of soil and weather conditions. Three examples that support this statement are as follows:
(1) Lettuce and Chard grows well in clayey soil.
(2) Wheat and sugarcane can be grown in a loamy soil.
(3) Carrots, Potato and Watermelon grow well in sandy soil.
Q. 5. What is soil erosion? How can it be avoided?
Answer: The removal of the top layer of the soil by different agents like wind and water, is called soil erosion. There are many other factors like overgrazing by animals, deforestation, industrial setups that increases the pace of soil erosion.
It can be avoided by planting more and more trees, keeping a check on deforestation and stopping overgrazing by animals. Land should not be used again and again and gaps should be taken in the rotation of crops too.
Q. 6. Why is it said that ‘plasticity’ and ‘cohesion, play an important role in the workability of a soil?
Both plasticity and cohesion are important for the soil. Cohesion means the soil particles stick to each other and bind the soil. It prevents the loosening of the soil.
Plasticity in the soil helps in giving different shapes to the soil. Earthen pots can be made because of this nature. Black soils are highly plastic in nature. So, this proves that both the properties of plasticity and cohesion are important for the workability of the soil.
So, these were DAV Class 7 Science Chapter 10 Solutions. If you have any queries, you can ask through the comment section below. Stay tuned to CareerAdvice4u for solutions to other chapters of the DAV Class 7 science book.
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