NCERT Solution class 7 Science Chapter-9

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NCERT Solution class 7 Science Chapter-9

Chapter – 9,      Soil

Chapter Exercise

Page no. – (105)

 

Tick the most suitable answer in questions 1 and 2.

Q.1– In additional to the rock particles, the soil contains

  1. Air and water
  2. water and plants
  • Minerals, organic matter, air and water
  1. Water, air and plants.

 

Ans.1– iii. Minerals, organic matter, air and water.

 

Q.2– The water holding capacity is the highest in

  1. Sandy soil
  2. Clayey soil
  • Loamy soil
  1. Mixture of sand and loam.

 

Ans.2– ii. Clayey soil.

 

Q.3– Match the items in column I with those in column II:-

Column I Column II
          i.              A home for living organism a)                       Large Particles
     ii.              Upper layer of the soil b)                      All kinds of soil
 iii.              Sandy oils c)                        Dark in colour
 iv.              Middle layer of the soil d)                      Small particles and packed tight
     v.              Clayey soil e)                       Lesser amount of Humas

 

Ans.3–

Column I Column II
           i.              A home for living organism b) All kinds of soil
       ii.              Upper layer of the soil c) Dark in Colour
  iii.              Sandy oils a) Large particles
  iv.              Middle layer of the soil e) Lesser amount of humus
       v.              Clayey soil d) Small particles and packed tight

 

Q.4– Explain how soil is formed.

Ans.4– Soil is formed by weathering of rocks. The weathering is the breakdown of rocks by physical breakdown and decomposition of minerals. Weathering is the breakdown of rocks by the action of wind, air and water. Soil formation is a slow process and it occurs every time.

 

Q.5– How is clayey soil useful for crops?

Ans.5– The clayey soil is useful for soil by the following reasons:-

  • Clayey soil is much rich in organic matter.
  • Clayey soil has a great ability to hold water.
  • Clayey soil is suitable soil for growing wheat.

 

Q.6– List the differences between clayey soil and sandy soil.

Ans.6–

  Clayey Soil Sandy Soil
1.                        Water holding capacity is a good Water holding capacity is a low
2.                        Air contain is low Air get trapped between the particles
3.                        Difficult to plough when wet Easy to plough when wet
4.                        Suitable for crops like wheat, gram and paddy Suitable for crops like Cotton, Peanuts and vegetable
5.                        It is fertile land It is infertile land

 

Q.7– Sketch the cross section of soil and label the various layers.

Ans.7–

Soil Profile

  • From Shutterstock.com

 

Q.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.

 

Ans.8–

Amount of water = 200 ml

Percolation time = 40 minutes

 

Percolation rate

= ­__amount of water in ml­­__

   Percolation time in minute

= ­__200 ml__

     40 minute

= 5ml/mins.

 

Q.9– Explain how soil pollution and soil erosion could be prevented.

 

Ans.9– Deforestation should be prevented and effort should be made to increase the green areas to prevent soil erosion and soil pollution.