NCERT Class VII Science Solutions: Chapter 9 – Soil Part 4

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Question 14:

Rajasthan is a desert state in India. Once while travelling to Rajasthan by train. Boojho observed several streams and rivulets of rain water during the journey but to his surprise he did not see streams of water in the desert region even during rains. Help Boojho find a suitable explanation for this.

Answer:

Deserts are vast stretches of sand where the falling rain water immediately percolates downwards in the spaces between sand particles. Due to this he did not see streams of water in the desert region.

Question 15:

Match the animals in Column I with their natural place of dwelling (habitat) in Column II

Match the Column I and Column II (Q)
Match the Column I and Column II (Q)

Column I

Column II

Earthworm

Sand and beaches

Garden lizard

Burrows in soil

Crab

Deep, narrow holes in dry soils

Rodents

Surface of soil

Scorpion

Surface of shaded moist soils

Snails and slugs

A horizon of moist soils.

.

Answer:

Match the Column I and Column II (A)
Match the Column I and Column II (A)

Column I

Column II

Earthworm

vi A horizon of moist soils.

Garden lizard

iv Surface of soil

Crab

i Sand and beaches

Rodents

ii Burrows in soil

Scorpion

iii Deep, narrow holes in dry soils

Snails and slugs

v Surface of shaded moist soils

LONG ANSWER QUESTIONS

Question 16:

Continuously water-logged soils are disadvantageous for plant growth. Why?

Answer:

Roots, although underground, possess living cells that require oxygen for respiration and production of energy. They absorb oxygen that is present in the spaces between soil particles. But in water-logged soils, water occupies the spaces between soil particles and pushes the oxygen out into the atmosphere. Thus, roots are deprived of oxygen and this affects root and plant growth.

Question 17:

Why is soil erosion relatively less in dense forests as compared to barren, open fields?

Answer:

Image of soil Erosion

Soil Erosion

Image of soil Erosion

In dense forests, the tree cover (canopy) prevents rain water from directly falling on the ground/soil. Also roots of the vegetation bind the soil particles and hold them together. As a result soil erosion is minimised.

But in barren, open fields the soil is exposed to the falling rain. The soil particles become loose due to the impact of raindrops and the flow of water carries them away. The flowing water further erodes the soil surface aggravating erosion.

Question 18:

Gardeners gently dig up the soil around the roots of garden herbs (plants) frequently. Give reasons.

Answer:

  1. For enabling easy root growth:

  2. For easier percolation of water:

  3. For aerating the soil/enabling air to get Into deeper layers of soil:

  4. For removing the weeds.