Tuesday , July 5 2022

NCERT 7th Class (CBSE) Science: Soil

Question: How does large variations between day and night temperatures causes weathering?

Answer: How does large variations between day and night, for example – In North India also causes weathering. The rocks expand during the day and contract during the night. Due to expansion and contraction this weakens the rocks and they crack and crumble.

Question: Distinguish between clay, silt and sand.

Answer: Distinguish between clay, silt and sand:

1. It has the smallest size particles less than .oo2 mm.
1. Silt has particles between .oo2 mm and .02 mm
 1. Sand has the largest sized particles (Diameter greater than 0.2 mm.)
2. It feels smooth. 
2. It is not smooth. 
one_third_last]2. It course to touch. [/one_third_last]
3. You cannot see single clay particle.
3. It is found in river bed.
3. It is found in deserts.

Question: Why is earthworm referred to as farmers friend?

Answer: Earthworms are called farmers friend. They improve the texture of the soil. By burrowing into the soil, they make it loose thus allowing air to enter into it and water to drain from it. They also forms channels in soil for roots to spread through.

Question: How is humus formed?

Answer: The dead plants and animals present in the soil get decayed by the action of bacteria and other microorganisms to form humus.

Question:Give difference between sandy soil and loamy soil.

Answer: The difference is as follows:

Sandy Soil
Loamy Soil
1. It contains large coarse particles, which is called sand.
1. It contains large and fine particles of sand, silt and clay.
2. It is gritty, with a very little humus and lot of air spaces between the particles.
2. It contains lot of humus./one_half_last]
3. This type of soil is very well aerated and cannot hold water for long
3. This type of soil is well aerated, it is the most fertile soil and proves to be ideal for plant growth.
4. This type of soil is found in places with warm climate such as deserts and marshy areas.
4. Silt is a type of soil formed due to depositions in river beds.

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