NCERT Exemplar Problems Class 7 Science – Soil

Question 1:
The microorganisms present in the soil require moisture (water) and nutrients for growth and survival. Choose from the options below, the habitat (place) where the soil has plenty of water and nutrients.
(a) Desert
(b) Forest
(c) Open field
(d) Cricket ground
Answer:
(b) The microorganism present in the soil having plenty of water and nutrients are present in the habitat of forest.

Question 2:
Availability of water and minerals in the soil for maximum absorption by roots is in the
(a) B-horizon
(b) C-horizon
(c) A-horizon
(d) Surface of soil
Answer:
(c) Availability of water and minerals in the soil for maximum absorption by roots is in A-horizon. A-horizon is called the topsoil and this layer is generally soft, porous and can retain more water.

Question 3:
Soil conservation measures are mainly aimed at protecting which of the following?
(a) Plants
(b) Topsoil
(c) Subsoil
(d) Soil organisms
Answer:
(b) Soil conservation measures mainly aim at protecting topsoil, which is rich in humus and nutrients making it fertile to grow plants.

Question 4:
Read the following statements with reference to soil.
(i) Weathering is a very fast process of soil formation,
(ii) Percolation of water is faster in sandy soils.
(iii)Loamy soil contains only sand and clay.
(iii) Topsoil contains the maximum amount of humus.
(iv) Choose the correct statements from the above.
(a) (ii) and (iv) (b) (i) and (iii) (c) (ii) and (iii) (d) (i) and (ii)
Answer :
(a) Statements (ii) and (Iv) are correct with reference to soil while (i) weathering is a slow process of soil formation and (iii) loamy soil consists of sand, clay and silt along with humus.

Very Short Answer Type Questions

Question 5:
Soil has particles of different sizes. Arrange the words given below in increasing order of their particle size.
Rock, clay, sand, gravel, silt
Answer:
The soil particles’ with the increasing order of their particle sizes can be shown as:
Clay < Silt < Sand < Gravel < Rock

Question 6:
The components of loamy soil are …………, ………………and …………………… .
Answer:
Sand, Silt and Clay

Question 7:
Read the following statements and give the appropriate terms for each of them.
(a)The process of breakdown of rocks by the action of wind, water, sunlight.
(b) Removal of topsoil during heavy rains or strong winds.
(c) Accumulation of wastes in the soil generated by human activity which alter the features of soil.
(d) The process of movement of water into deeper layers of soil.
Answer:
The terms for the above described statements are as follows:
(a) Weathering
(b) Soil erosion
(c) Soil pollution
(d) Percolation

Question 8:
Unscramble the following jumbled words related to soil.

Answer:
(a) HUMUS
(b) SOIL PROFILE
(c) HORIZON
(d) LOAM
(e) WEATHERING
(f) PERCOLATION

Short Answer Type Questions

Question 9:
Which of the following situations — ‘A’ or ‘B’ — is advantageous for absorption of water and minerals ? why?
Situation ‘A’ : Growth and branching of roots in the C-horizon.
Situation ‘B’ : Growth and branching of roots in A and B-horizons.
Answer:
Situation ’B’ is advantageous for absorption of water and minerals. This is because A-horizon is top iaysr o^f soil and is rich in minerals and humus. The plant roots grow in the topsoil. The roots of some or the frees are however, able to reach B-horizon (subsoil). Subsoil is also rich in soluble minerals.

Question 10:
How can a farmer convert acidic soil into neutral soil?
Answer:
The farmer can convert acidic soil into neutral soil by adding a small quantify of quicklime or slaked lime solution to the soil. Quick lime and slaked lime are bases and hence, react with the excess acid present in the soil and reduce its acidity.

Question 11:
Is it a good practice to remove grass and small plants that are growing in an open, unused field? Give reason to support your answer.
Answer:
No, it is not a good practice to remove grass and small plants growing in an open, unused field because the plants cover the soil surface. Their roots bind the soil particles, holding and adhering them in place.
It helps in preventing the topsoil from being washed off during heavy rain, floods and winds. In this way, soil erosion is prevented and top soil layer is preserved for growing more plants.

Question 12:
A man digging a pit found that he could dig with ease initially but digging became difficult as he went deeper. He could not dig beyond a depth 5 feet. Provide a suitable scientific explanations.
Answer:
The man digging a pit could dig with ease initially because of the presence of topsoil and subsoil (mainly comprising cl humus and nutrients). But as he digs deeper, he finds it difficult to dig beyond a depth of 5 feet as lower layers are made up of small partially weathered rocks with cracks, crevices and with bedrock which make it hard to dig.

Question 13:
Locate the following zones given as boxed items in figure which shows a diagram of soil profile

Topsoil, subsoil, C-horizon, bedrock
Answer:

Question 14:
Rajasthan is a desert state in India. Once while travelling to Rajasthan by train, Boojho observed several streams and rivulets of rainwater during the journey but to his surprise, he did not see streams of water in the desert region even during rains. Help Boojho to find a suitable explanation for this.
Answer:
Deserts are made up of sand, thus when the rainwater falls on land, it percolates immediately downwards in the spaces between sand particles. So, the streams of water in desert region are not visible even during rainy season.

Question 15:
Match the Column I with Column II.

Answer:
The correct matching is as given
(a)-(vi), (b)-(iv), (c)-(i), (d)-(ii), (e)-(iii), (f)-(v)

Question 16:
Continuously water-logged soils are disadvantageous for plant growth. Why?
Answer:
Roots although underground possesses 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 spaces between soil particles and pushes the oxygen out into the atmosphere. Thus, roots are deprived of oxygen and this affects the plant growth.

Question 17:
Why is soil erosion relatively less in dense forests as compared to barren, open fields?
Answer:
In dense forests, the tree cover (canopy) prevents rainwater from, directly falling on the ground/soil. Also, the roots of 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 failing 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:
(i) it enables easy root growth.
(ii) for easier percolation of water.
(iii) for aerating the soil enabling air to get into deeper layers of soil.
(iv) for removing the weeds.

Question 19:
In towns and cities generally, the borewells have to be dug very deep to get water as compared to borewells dug in villages. Give suitable reasons.
Answer:
The borewells have to be dug very deep in towns and cities to get water as compared to those in villages because
(i) excessive use of water in towns, depletes the groundwater.
(ii) towns and cities have asphalted roads and vast areas of soil are concreted. As a result, rainwater cannot percolate to recharge groundwater and the groundwater level further decreases.
Villages have larger areas of open soil surface and fewer asphalted roads and concrete surfaces. Thus, larger soil surface area is available for rainwater to percolate into the soil easily and recharge the groundwater. As a result, even shallow borewells yield water.

Question 20:
Several terms related to soil are hidden in the squares given as figure, spot them and make a list. Two examples are given for you.

Answer:

Humus, sand, water, clay, gravel, weathering, horizon, percolation, mineral, plant, erosion, profile, silt.