Class 7 Science

Soil

NCERT Solution

Tick the most suitable answer in questions 1 and 2.

Question 1: In addition to the rock particles, the soil contains

(i) air and water
(ii) water and plants
(iii) minerals, organic matter, air and water
(iv) water, air and plants

Answer: (iii) minerals organic matter, air and water

Question 2: The water holding capacity is the highest in

(i) sandy soil
(ii) clayey soil
(iii) loamy soil
(iv) mixture of sand and loam

Answer: (ii) Clayey soil


Question 3: Match the items in Column I with those in Column II:

Column AColumn B
(1) A home for living organisms(a) Large particles
(2) Upper layer of soil(b) All kinds of soil
(3) Sandy soil(c) Dark in colour
(4) Middle layer of soil(d) Small particles and packed tight
(5) Clayey soil(e) Lesser amount of humus

Answer: 1 → b, 2 → c, 3 → a, 4 → e, 5 → d

Question 4: Explain how soil is formed.

Answer: Soil is formed by the process of weathering. The breaking down of rocks because of the action of wind, rain, ice, etc. is called weathering.

Question 5: How is clayey soil useful for crops?

Answer: Clayey soil can retain much water and consequently contains lot of moisture even in summer. That’s why it is most useful for crops like paddy which requires lot of water. Clayey soil is useful for wheat also.



Question 6: List the differences between clayey soil and sandy soil.

Answer:

Clayey soilSandy soil
Particles are of very small sizeParticles are of quite large size
Particles are tightly packed togetherParticles are not closely packed
Not aerated enoughWell aerated
Can retain water for long timeCannot retain water
Water does not drain easilyWater drains easily
FertileNot fertile
Suitable for many cropsNot suitable for crops

Question 7: Sketch the cross section of soil and label the various layers.

Answer:

soil profile



Question 8: Razia conducted an experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.

Answer: Given, Time = 40 minute
Volume of water = 200 ml
Percolation rate = amount of water in mL ÷ time taken for percolation
= 200 mL ÷ 40 min = 5 mL per minute

Question 9: Explain how soil pollution and soil erosion could be prevented.

Answer: Soil pollution and soil erosion could be prevented using following:

  • Plantation
  • Better farming method, like crop rotation and mixed farming
  • Use of manure instead of synthetic fertilization.
  • Use of natural pesticides.
  • Avoid dumping non-biodegradable items in soil.
  • Terrace farming in hilly areas.