Here in this post we provided NCERT Exemplar Problem Class 7 Science Soil Chapter 9 Full Explanation by group of Science Experts. We have provided here each questions answer with reason behind the answer.
Hope it help you!
Soil Class 7 Exemplar full Explanation:
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.
I) Desert
II) Forest
III) Open field
IV) Cricket ground
Answer:-b) forest
Forest is the habitat where the soil has plenty of water and nutrients.
2) Availability of water and minerals in the soil for maximum absorption by roots is in the –
I) B- horizon
II) C- horizon
III) A- horizon
IV) Surface of soil
Answer:-c) A- horizon
A – horizon or topsoil has the availability of water and minerals in the soil for maximum absorption by roots .
3) Soil conversation measures are mainly aimed at protecting which of the following ?
A) Plants
B) Top soil
C) Sub soil
D) Soil organisms
Answer:- b) Top soil
Soil conservation are mainly aimed for the protecting top soil. Because plants are grown and dependable for the water and nutrients on the top soil .
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.
IV) Top soil contains the maximum amount of humus.
Choose the correct statement from the above.
A) II and IV
B) I and III
C) II and III
D) I and II
Answer:- a) II and IV
Percolation of water is faster in sandy soil and top soil contains the maximum amount of humus.
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Very Short Answer Questions
5) Soil has particles of different sizes. Arrange the words given below in increasing order of their particle size.
Rock, clay ,sand ,Gravel, slit
Answer:-
Rock → Gravel → Sand → Slit → clay
6) The components of loamy soil are _________, ________, and __________.
Answer:-
The components of loamy soil are sand , slit and clay.
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.
Answer:- Weathering
B) Removal of top soil. During heavy rains or strong winds.
Answer:- Erosion
C) Accumulation of wastes in the soil generated by human activity which alter the features of soil.
Answer:-soil pollution
D) The process of movement of water into deeper layers of soil.
Answer:- percolation
8) Unscramble the following jumbled words related to soil.
a) S U H U M
b) I L O S F I P R O L E
c) Z O I N O R H
d) M O A L
e) G I N R H E T W E A
f) A T O N I E R P C L
Answer:-
1) HUMUS
2) SOIL PROFILE
3) HORIZON
4) LOAM
5) WEATHERING
6) PERCOLATION
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Short Answers Questions
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 more advantageous for the absorption of water and minerals be the branching of roots. In situation B there are A horizon and B horizon. A- horizon or topsoil is the uppermost layer which is soft, moist, porous and it retains more water. Topsoil is generally dark in colour and large amount of humus and nutrients and minerals are present in it.
Another layer in the situation B contains B- horizon. Below the A-horizon there is B- horizon or middle layer is present. B- horizon has small amount of humus but large amount of minerals are present. This layer is slightly harder and compact than A horizon. It is also called as subsoil.
But in situation A where only rocks are present is the C- horizon which does not contain any humus , minerals, nutrients, water retain capacity, hard layer etc. Therefore these is not suitable for the growth of roots .
Thus situation B type of soil is very much suitable for the growth of branching of roots therefore it is advantageous.
C- Horizon
Situation ‘A’
A and B Horizons
Situation ‘B’
10) How can a farmer convert acidic soil to neutral soil ?
Answer:- Due to the large amount of chemical fertilizers soil gets more Acidic or basic . Due to these very Acidic or very basic character of soil, crop quality does not retained by the soil. For that soil must be given the dose of opposite substances so that the soil gets neutral.
Now there is soil which is very Acidic, so that there should be addition of small quantity of slaked lime or quick lime solution in the soil by the farmer. As the quick lime is basic in nature, After adding in the Acidic soil it will be neutral.
11) It is 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. Removing small plant growing in open Unused field is not good practice at all. Because plants cover the soil from the top level. These small plant covers the soil area and their roots binds the soil particles. As in the rainy season soil can flow away with water if plants are not there. This causes the loss of soil. Also during the strong wind it can be blown away with the air and thus the soil erosion occurs . This erosion of soil can be prevented by the small plants which are grown in open fields. Thus it should not be removed.
12) A man digging a pit found that he could dig with case initially but digging became difficult as he went deeper. He could not dig beyond a depth of 5 feet. Provide a suitable scientific explanation.
Answer:- As the uppermost layer which is topsoil or A- horizon is soft , moist, porous and have loose binding between the soil particles. Thus it is easy to dig in the topsoil. But as going inside the topsoil, there is subsoil or B-horizon which is slightly hard as compared to A- Horizon. Where the soil is compact. Going inside the B- horizon there are partially weathered rocks present which is also called as C- horizon. It is hard layer due to rocks. Under that Bedrock is present which is the most hard layer of the soil. Thus digging became difficult as he went deeper.
13) Locate the following zones given as boxed items in figure 9.1 which shows a diagram of soil profile.
Top soil , subsoil, C- horizon
Answer:
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:- Rajasthan is a desert in India, where the there is only sand over the complete area. In the desert only sandy soil is present Which contains the greater proportion of big particles. Sand particles are large in size. This type of soil i.e sand is well aerated. The large particles of sand can not fix to each other or close together. Thus there are gapes in between the soil particles, which is filled by the air. Due to this water can drain in large quantity and quickly through the sand. There is difference between the types of soils and their water retaining capacity also the Percolation rate of soil.
Therefore even during the rains water desert absorbed the whole water as the large water drainage capacity of sand.
(15) Match the animals in column I with their natural place of dwelling ( habitat ) in column II.
Column I | Column II |
a) Earthworm | I)Sand and beaches |
b) Garden lizard | II) burrows in soil |
c) Crab | III) deep, narrow holes in dry soils |
d) Rodents | IV) surface of soil |
e) Scorpion | V) surface of shaded moist soils |
f) Snails and slugs | VI) a Horizon of moist soils. |
A) Earthworm→ vi) a Horizon of moist soils.
B) Garden lizard→ iv) surface of soil
C) Crab→i) sand and beaches
D) Rodents→ ii) burrows in soil
E) Scorpion→ iii) deep, narrow hole in dry soils
F) Snails and slugs→ v) surface of shaded moist soils
16) Continuously water – logged soils are disadvantageous for plant growth. Why?
Answer:- Continuously water logged soil is clayey soil. Clayey soil has the higher proportion of fine particles. These clay particles are much smaller or fine . They packed together without large gapes. As there are small gaps there is only little space for the air. Due to the compactness of the clay particles water held capacity is more in these soi. Due to which the air does not have more space, resulting in the less oxygen. As the water takes place in between gaps oxygen is transferred to the surrounding. Therefore these soil has less oxygen. But roots of plants need water , nutrients , minerals as well the oxygen for their growth. Due to continuously water logging soils roots does not get enough oxygen and plant does not grow.
17) Why is soil erosion relatively less in dense forests as compared to barren, open fields?
Answer:- In the dense forest there are large trees planted over the area. These trees are large in size also they are compact. Due to these plants sunlight does not directly fall on soil. This prevents the heating up of soil. During the rainy season small water droplets does bot directly get in contact with soil. The roots of trees bind the soil particles and hold them tightly packed. Therefore during the rain soil does not flow away with water. These prevent the erosion of soil Or soil erosion can be minimised.
While in the barren or open field the soil is directly exposed to the sunlight, also in rainy season soil flow away with heavy water. In the heavy wind soil flew with air .No plats are there thus no soil is binded with the roots thus the soil is loose over there. This causes erosion of soil in large quantity. Therefore in dense forest soil erosion is relatively less .
18) Gardeners gently dig up the soil around the roots of garden herbs ( plants ) frequently. Give reasons.
Answer:- Gardeners gently dig up the soil around the roots of garden herbs (plants) frequently because first of all roots should not be damaged due the digging process. As if roots are damaged then plant may die or it will not grow healthy.
Digging process slightly aerated the soil so that the air should go Inside deeper layers of soil which will provide more oxygen to the plants.
These will become easy to growth of plants.
Digging of topsoil will make easy for percolation of water in the soil. That will make the plant available more water. Retaining capacity will be more.
Also the weeds growing around the plants should be removed as they are competitive of the plants in the water and nutrients, but weeds are of no use.
19) In towns and cities, generally, the bore wells have to be dug very deep to get water as compared to bore wells dug in villages. Give suitable reasons.
Answer:-The storage of water in large quantity is generally deep inside the rocks layer.
In the cities or towns there are so many concrete houses are present also large area is under construction of roads which is made up of concrete over the soil. Therefore soil can not retained the water as there is not so much of space for the percolation of raining water. Therefore the water level goes on decreasing in the Town.
As in the villages there are not so much concrete roads. There are larger area of soil which can easily percolate the water during the rainy season. And maintain the water level inside . Large amount of water percolation large quantity of the water in the earth. These percolation increase the level of water inside the soil . Thus in the city or towns the bore wells have to be dug very deep inside as compared to the villages.
20) Several terms related to soil are hidden in the squares given as figure 9.2 spot them and make a list . Two examples are given for you.
humus, sand, water, clay, erosion, gravel, weathering, percolation, Horizon, plant , profile, minerals.
Answer:-