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Class seven science Soil chap 9 additional Questions
Chapter 9: Soil
Additional questions
Objective Questions
A. State whether the following statements are true or false:
1. Only the presence of fertilisers on the ground is enough for growing crops———–.
2. The minerals present in water do not affect the process of measuring the correct percolation rate of soil————–
3. Crabs are found in sand and beaches———–.
4. Snails and slugs are usually found in deep holes in dry soils.————-
5. Water-logging in a crop field helps in the growth of plants————–.
Answers: 1. False 2. True 3. True 4. False 5. False.
Match the following:
Ans
Very Short Answer Type Questions
1. Name the uppermost layer of earth.
Answer: The uppermost layer of the earth is called the crust.
2. Write two important things which are not possible without soil.
Answer: Two important things which are not possible without soil are:
1. Growing of crops
2. Life of microorganisms
3. Name the soil which is good to grow cereals.
Answer: Loamy soil is good to grow cereals.
4. Write any one practice to prevent soil erosion.
Answer: Plant more trees to prevent soil erosion.
5. Write the composition of the soil.
Answer: The composition of the soil is: Rock particles, minerals, humus, air, water and living organisms.
6. Name the bottom-most layer of the soil profile.
Answer: The bottom-most layer of the soil profile is called the bedrock.
7. What is silt?
Answer: The rock particles in the soil which are little larger than clay particles from silt.
8. Which soil has minimum air space?
Answer: Clayey soil has minimum air space.
Short Answer Type Questions
1. What is soil?
Answer: Soil is the uppermost layer of the earth’s crust. It is a brown-solid material which is made up of rock particles, minerals, humus, air, water and living organisms.
2. When soil is mixed with water, it divides into different layers. Name the materials present in the different layers from top to bottom.
Answer: The materials present in soil from top to bottom are humus, water, clay, sand and gravel.
3. What is meant by weathering?
Answer: The breaking down of rocks due to the action of heavy wind, rains or extreme climatic to form soil is called weathering.
4. What is humus?
Answer: The rotting dead and decaying matter in the soil is called humus.
5. Write the formula to calculate the percolation rate.
Answer: The formula to calculate the percolation rate is,
Percolation rate of water in soil =
6. How would you calculate the percentage of water absorbed by soil?
Answer: We can calculate the percentage of water absorbed by soil using the following formula, Percentage of water in soil =
7. How will you identify the type of your garden soil? Write any one method.
Answer: We can identify the type of soil in our garden by holding the soil in hand and pressing it to form a ball. If it holds tightly then it is clayey soil.
If it does not hold at all it is sandy soil and if it holds but moves through our fingers, it is loamy soil.
8. Why do people want plastics and polythene bags to be banned?
Answer: Plastics and polythene bags are not good for the fertility of the soil. They release toxic gases while dumping them underground or when burning them. They kill the organisms living underground. They do not degrade easily and are the main reason for soil pollution.
9. During rain, the soil covered by plants is not easily washed away as compared to the bare soil. Give a reason for your answer.
Answer: The roots of the plants hold the soil particles very tightly and prevent it from moving. On the other hand, the bare soil does not have enough vegetation to hold the soil particles, so it gets easily washed off during rain.
10. What is soil erosion? What are the reasons of soil erosion?
Answer: The removal of the topmost layer of the soil due to heavy rains or wind is called soil erosion. It occurs in places where vegetation is scarce i.e. it is less than required. Deforestation is one of the main reasons of soil erosion because after cutting down trees there are no roots of the plants to hold the soil firmly and prevent it from getting washed off from the ground by any means.