The DAV Class 7 Science Solutions and DAV Class 7 Science Chapter 10 Question Answer – Soil are essential study tools for DAV public school students in Class 7.
DAV Class 7 Science Ch 10 Question Answer – Soil
DAV Class 7 Science Ch 10 Solutions – Soil
Something To Know
A. Fill in the blanks.
1. Various layers in the soil are called ________
Answer:
Soil Horizons
2. The intermediate particles, that are neither very rough, nor too smooth, are termed as ________
Answer:
Silt
3. ________ is the tendency of similar particles to stick to one another.
Answer:
Cohesion
4. Soil air is important for roots to carry out ________
Answer:
Breathing,
5. ________ and ________ cause soil pollution.
Answer:
insecticides, fertilizers
B. Match the following:
| Column A | Column B |
| 1. Potter’s soil | (a) No percolation |
| 2. Organic material | (b) Clay |
| 3. Vermicompost | (c) Well aerated |
| 4. Sandy soil | (d) Humus |
| 5. Concrete floor | (e) Earthworm |
Answer:
| Column A | Column B | |
| 1. Potter’s soil | b | (a) No percolation |
| 2. Organic material | d | (b) Clay |
| 3. Vermicompost | e | (c) Well aerated |
| 4. Sandy soil | c | (d) Humus |
| 5. Concrete floor | a | (e) Earthworm |
C. Tick (✓) the correct option.
1. Which of the following is not an agent of physical weathering?
(a) Wind
(b) Temperature
(c) Water
(d) Organic acids
Answer:
(d) Organic acids
2. Which of these is the lowest horizon of soil profile?
(a) Subsoil
(b) Bed rock
(c) Gravel
(d) Humus
Answer:
Bed rock
3. Which organism is known as nature’s ploughman?
(a) Honeybee
(b) Rat
(c) Bird
(d) Earthworm
Answer:
(d) Earthworm
4. Which soil can retain more water?
(a) Sandy soil
(b) Clayey soil
(c) Loamy soil
(d) Polluted soil
Answer:
(b) Clayey soil
5. Coconut trees thrive in coastal region where the soil present is mainly
(a) Clayey soil
(b) Loamy soil
(c) Sandy soil
(d) Sandy loam
Answer:
(d) Sandy loam
D. Answer the following questions in brief.
Question 1.
State the meaning of the term ‘soil’.
Answer:
Soil is the naturally occurring, loose covering of broken rock particles and decaying organic matter (humus) on the surface of the earth which can support life.
Question 2.
List the four main agents of physical weathering.
Answer:
Four main agents of weathering are as follows:
- Temperature
- Water
- Wind
- Plants
Question 3.
Write one difference between sand, clay and silt.
Answer:
| Sand | Clay | Silt |
| Large particles | Small particles | Medium-sized particles |
Question 4.
Name the types of soil classified on the basis of soil texture.
Answer:
On the basis of soil texture, soil is classified as follows:
- Sandy soil
- Clayey soil
- Loamy soil
Question 5.
Give the meaning of the term ‘Cohesion’.
Answer:
The property of similar particles to stick together is called cohesion.
Question 6.
List any three causes of soil pollution.
Answer:
Three causes of soil pollution are as follows:
- Chemicals
- Radioactive materials
- Toxic compounds
E. Answer the following questions.
1. Classify, and explain, the categories of soil on the basis of ‘texture of the soil’.
Answer:
On the basis of texture, soil is classified as follows:
(a) Sandy soil: This type of soil is composed of bigger particles. The soil is well aerated. This type of soil cannot retain water because water drains out quickly. Sandy soil is not fit for farming.
(b) Clayey soil: This soil has a higher proportion of fine and smooth particles. This type of soil is not well aerated but can retain a lot of water. This type of soil leads to the problem of water logging in field.
(c) Loamy soil: This soil is a mixture of sand, silt and clay particles. It can hold reasonable amount of water and air. This soil is best for farming.
Question 2.
Differentiate between infiltration rate and percolation rate.
Answer:
The rate at which water enters the soil is called infiltration rate. The rate at which water moves through soil is called percolation rate. A soil with a higher infiltration rate but moderate percolation rate is good for farming.
Question 3.
Write a short note on ‘composition of soil’.
Answer:
The following components are generally found in soil:
- Inorganic substances: Most of the inorganic components of soil are derived from the parent rock.
- Organic material: The organic matter mainly comes from dead and decaying parts of plants and animals. This high humus content means the soil would be highly fertile.
- Air and water: Air and water are also present in soil. These are required by plants for their survival.
- Living organisms: Many organisms are present in soil. Apart from many microbes, some insects and small creatures also live in soil.
Question 4.
The type of crop that may be grown in a particular field depends on the type of soil’. Give three examples in support of this statement.
Answer:
Three examples which support this statement are as follows:
- Rice grows well in clayey soil.
- Wheat grows well in loamy soil.
- Cotton grows well in sandy loam or loamy soil.
Question 5.
What is soil erosion? How can it be avoided?
Answer:
The removal of topsoil by agents of weathering is called soil erosion. Soil erosion can be prevented by afforestation practices. Afforestation involves planting trees on bare lands and nearby fields. Better
farming practices also help in preventing soil erosion.
Question 6.
Why is it said that ‘plasticity’ and ‘cohesion’, play an important role in the workability of soil?
Answer:
Because of plasticity, a particular type of soil can be given any shape. Sandy soil is non-plastic, while clayey soil is plastic in nature. Plastic soil is cohesive in nature which means the particles of soil stick together. Unlike sandy soil; clayey soil, can be used for making earthenware. This shows that plasticity and cohesion play an important role in the workability of soil.
Value Based Question
On the ‘opening day’, the school principal, and teachers, welcomed the parents and guardians of their ‘new students’. The principal went on to say that the parents and the teachers, both have a crucial role to play, in the growth and development of the children. She compared their roles with the role of the physical and chemical agents that cause the weathering of the soil and make it suitable for supporting, and sustaining, the growth of all forms of life.
Question 1.
State any two of the values that parents/teachers generally display during the growth of their children.
Answer:
Caring approach, being a friend and guide for children.
Question 2.
Write, in brief, the role of (i) Plants and animals (ii) Solvent action of water in the ‘weathering’ of the soil.
Answer:
Role of plants and animals: Lichens and mosses grow on bare rocks and cause gradual disintegration of rocks. Grasses, shrubs and trees also break rocks because their roots enter the crevices in the rocks. Animal droppings also have similar effect. Solvent action of water: Rains and flowing water dislocate the soluble particles on the rocks. Thus, they expose the inner portion of rocks to agents of weathering.
Something To Do
Question 1.
Visit a potter: Potters are difficult to find in cities. Try finding such a place, and visit it with your teacher and classmates. Observe the texture of the soil used by the potter. Can he make pots using sand? How does the property of plasticity differ in sand and clay?
Answer:
Potter uses clayey soil, but he cannot use sandy soil. Plasticity of soil is negligible in sandy soil, while it is very high in clayey soil.
Question 2.
Take three pots and fill them with sand, clay and loamy soil. Sow wheat grains, or seeds of green gram, in each of these pots. Water them regularly. using the same amount of water for each pot. Record your observation about the growth of the plants. What do you infer?
Answer:
It is observed that wheat does not grow in sandy soil. Wheat grows to a certain extent in clayey soil, but it grows the best in loamy soil.
Question 3.
Make a group of six. Find out the main crops grown in any three states of India. Also find out the types of soil they are grown in. Make a PowerPoint presentation on your report.
| State | Main crop | Soil type |
| Bihar | Rice | Clayey soil |
| Punjab | Wheat | Loamy soil |
| Tamil Nadu | Rice | Loamy soil |
Make the PowerPoint presentation yourself.
DAV Class 7 Science Chapter 10 Solutions – Soil
I. Fill in the blanks.
Question 1.
________ is present in the topmost layer of soil profile.
Answer:
Humus
Question 2.
________ is composed of parent rocks which are not broken.
Answer:
Bedrock
Question 3.
________ soil can retain highest amount of water.
Answer:
Clayey
Question 4.
________ soil can retain the least amount of water.
Answer:
Sandy
Question 5.
Cactus and acacia grow well in ________ soil.
Answer:
sandy
Question 6.
Living organisms cause ________ weathering of rocks.
Answer:
chemical
II. Tick (✓) the correct option.
1. Which horizon is also known as topsoil?
(a) O
(b) A
(c) B
(d) C
Answer:
(a) O
2. Which horizon is also known as subsoil?
(a) O
(b) A
(c) B
(d) C
Answer:
(c) B
3. Which are the first plants to grow on weathered rocks?
(a) Mosses
(b) Pine
(c) Flowering plants
(d) None of these
Answer:
(a) Mosses
4. Which property of soil makes it ideal for making pots?
(a) Percolation
(b) Plasticity
(c) Aeration
(d) Composition
Answer:
(b) Plasticity
5. The soil is red in colour because of which of these?
(a) Calcium
(b) Tin
(c) Iron
(d) Zinc
Answer:
(c) Iron
III. Answer the following questions in brief.
Question 1.
Define soil. Why is it said that most of the life on earth depends on soil?
Answer:
Soil is the naturally occurring, loose covering of broken rock particles and decaying organic matter (humus) on the surface of the Earth which can support life. All the living beings depend directly or indirectly on plants for food. Most of the plants grow on soil. Hence it is said that most of the life on earth depends on soil.
Question 2.
How does chemical weathering take place?
Answer:
Organic acids released during the decomposition of organic matter lead to weathering of rocks. Salts dissolve in water and the solution causes weathering.
Question 3.
Write a short note on composition of the soil.
Answer:
Soil contains inorganic substances; like minerals. Soil contains dead and decaying matters. Soil also contains some living creature. Additionally, water and air are present in gaps between soil particles.
Question 4.
Why is soil considered to be an important natural resource?
Answer:
Soil is an important resource for us. We get food from plants and plants need soil to grow. Soil is an important component in mining and construction industries. Soil is the habitat for many organisms.
Question 5.
How does soil get polluted?
Answer:
Accumulation of toxic compounds, chemicals, salts, radioactive materials, or disease causing agents; which can have adverse effect on plant and animal health; is called soil pollution. Chemical pesticides, excessive use of fertilisers and contamination of surface water are major causes of soil pollution,
Question 6.
The type of crop that may be grown in a particular field depends on the type of soil. Give two examples to support the statement.
Ans.
Wheat grows well in loamy soil. Cotton grows well in sandy loam soil. These two examples show that the type of crop that may be grown in a particular field depends on the type of soil.
Question 7.
Draw a neat, well labelled diagram showing soil profile.
Answer:
The diagram given alongside shows soil profile.
Question 8.
What is soil erosion? How can it be prevent?’4!’
Answer:
Soil Erosion: The removal of topsoil by agents of weathering is called soil erosion. Human activities hasten the rate of soil erosion and aggravate the situation. Plants prevent soil erosion because they hold the topsoil in place Soil erosion can be prevented by afforestation practices. Afforestation involves planting trees on bare lands and nearby fields.
IV. Answer the following questions.
Question 1.
What is weathering?
Answer:
A combination of physical, chemical and biological process on rocks is called weathering. It leads to soil formation.
Question 2.
How does water bring about weathering of rocks?
Answer:
Flowing water washes away the broken particles of rocks and deposits them somewhere else as sediment. Further, the flowing water also exposes the underlying rocks to different weathering agents.
Question 3.
What is soil profile?
Answer:
Arrangement of different layers of soil is called soil profile.
Question 4.
Write a brief note on sandy soil.
Answer:
This soil is composed of bigger particles. This soil is well aerated. This type of soil cannot retain water because water drains out quickly. Sandy soil is not fit for farming.
Question 5.
Write a brief note on clayey soil.
Answer:
This soil has a higher proportion of fine and smooth particles. This type of soil is not well aerated but can retain lot of water. This type of soil leads to problem of water logging in the fields.
Question 6.
Explain plasticity and cohesion of soil.
Answer:
Because of plasticity, a particular type of soil can be given any shape. Sandy soil is non-plastic, while clayey soil is plastic in nature. Plastic soil is cohesive in nature which means the particles of soil stick together.
V. Differentiate between:
Question 1.
Physical and chemical weathering of rocks.
Answer:
Physical weathering involves breaking of rocks into fine particles. Chemical weathering, on the other hand, involves changing the chemical composition of rock particles.
Question 2.
Infiltration and percolation of water.
Answer:
Absorption of water by the soil depends on infiltration and percolation rate. The rate at which water enters a soil is called infiltration rate. The rate at which water moves through soil is called percolation rate.
VI. Projects
Question 1.
Collect some soil from a nearby park or garden. Observe its colour and composition. Identify the type of soil in this case.
Answer:
Do it yourself.
Question 2.
Collect some soil from a nearby park or garden. Crush it to make fine powder. Mix a handful of soil in a beaker which is filled with water. Allow the water to stand. Observe the soil profile in beaker. Make notes in your notebook.
Answer:
Do it yourself.