Page 72 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

8. Name and write about agents of mechanical weathering.

Ans. The agents of mechanical weathering are as follows :
Temperature: In the day time, due to extreme heat of the Sun, rocks expand from

outside but remain cool from the inside. At night, the temperature drops due to
which rocks cool down and contract. This continuous cycle of uneven expansion and

contraction breaks them. This process is known as exfoliation.
Frost action: At times, water enters the cracks in the rocks. When water freezes in

these cracks, it expands, which leads to the expansion of the cracks. This further
leads to breaking down of the rocks into smaller pieces.

Gravity: Gravity leads to landslides, that is, falling of large rocks from steep slopes.
During landslides, the upper layer of the Earth and rocks become loose and the force

of gravity pull this loose layer downwards. Collision of rocks as they come down
results in breaking of big rocks into smaller ones and further into soil.

Wind and water: Moving wind and water carry small rocks along with them and
tend to have an abrasive effect. This too results in breaking down of rocks into small

granular structures.
9. Why are earthworms called farmer’s friends?

Ans. Many organisms also help to make the soil rich, such as earthworms. They live deep
in the soil and make it porous. This increases the water-holding capacity of the soil.

They also decompose dead plant and animal waste, just like fungi and bacteria and
increase the fertility of the soil. Therefore, earthworms are said to be a farmer’s

friend.
10. Draw a diagram to show different layers of soil.

Ans.

Different layers of soil

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