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DAV CLASS 7 The Earth and the Changes on It Question and Answer
A. Tick the correct option.
1. Which one of the following is not a human activity?
(a) diverse land use
(b) Cleaning of forest
(c) new human settlements
(d) formation of mountains
1. (d) formation of mountains
2. Which one is a Continental glacier?
(a) Siachin
(b) Antartica
(c) Gangotri
(d) Yamunotri
2. (b) Antarctica
3.Which of the following features are formed by a river?
(a) ‘V’ shaped valley, meander and delta
(b) ‘U’ shaped valley, meander and delta
(c) ‘I’ shaped valley, cliff and delta
(d) ‘V’ shaped valley, meander and sand dunes
3. (a) ‘V’ shaped valley, meander and delta
4. Which layer of the soil contains humus?
(a) bed rock
(b) weathered rock
(c) sub soil
(d) top soil
4. (d) top soil
5. Which soil type is capable of retaining moisture and becomes sticky when wet?
(a) alluvial soil
(c) red Soil
(b) black soil
(d) laterite soil
5. (a) alluvial soil
B. Fill in the blanks.
1. Organic matter when gets decomposed in the soil and converts it into dark coloured material is called ___________.
2. ___________ soil is found in a large part of our country.
3. ___________ and ___________ valleys are formed at the youthful stage of a river.
4. A ___________ is a steep sided rock facing the sea.
5. ___________ river and ___________ river form the largest delta of the world.
Answer: (1) humus (2) Alluvial soil (3) I shaped, V shaped (4) cliff (5) Ganga, Brahmaputra
C. Give a single term for each of the following statements.
1. Mounds of sand deposited by wind action in deserts.
2. The process in which a gradual wearing and carrying away of soil particles takes place on the earth’s surface.
3. The process of laying down of sediments carried by various agents of gradation.
4. A mass of moving ice down the slope.
5. Removal of the top layer of soil.
Answer: (1) Sand dunes (2) Erosion (3) Deposition (4) Glacier (5) Soil erosion
D. Answer the following questions in brief.
1. Specify two differences between internal and external forces.
Ans: The forces which act under the earth’s surface are called internal forces. They result in the change of landforms. Mountains are made because of internal forces While the forces which act on the earth’s surface are called external forces. They result in the change in nature and the shape of landforms.
2. Name the various agents of gradation.
Answer: The various agents of gradation are running water, wind, moving ice, sea weaves, etc.
3. Distinguish between transported and residual soil.
Answer: The formation of soil in which the weathering process breaks the rocks into small particles. These are then carried away by water, wind, etc., and later get deposited at a new place. Such soil is called transported soil.
When the soil is formed by the weathering of a parent rock and remains present on the same site, it is called residual soil.
4. How is a delta formed?
Answer: Before meeting the sea, the river becomes large and sluggish and gets divided into several distributaries. It now comes to its old stage. The river, thus, deposits silt, sand and sediments over a large area near its mouth. This large deposition helps in the formation of a delta.
5. Why is humus formed more rapidly in humid areas?
Answer: Humus is formed rapidly in humid areas due to the heavy growth of plants and rich animal life.
E. Answer the following questions.
1. Explain weathering. Mention the factors that affect the rate of weathering and soil erosion.
Answer: Weathering is the process, which breaks rocks into smaller particles. It includes erosion and deposition.
The factors that affect the rate of weathering and soil erosion are the temperature of the place, vegetation cover, rainfall, slope of the land, type of soil and changes in land use.
2. Explain the formation of soil with the help of a labelled diagram.
Answer: The formation of soil is a very slow process. It takes thousands of years to form a thin layer of soil. It is formed by the process of weathering. The soil forming process continues over a long span of time.
It starts developing in layers one over the other. These layers are called horizons. From bottom to top, the lowest horizon is called bed rock, then comes the horizon of weathered rock and it is followed by the sub soil and top soil.
3. What are the major soil types found in India? Give one important characteristic of each.
Answer: The major types of soil found in India are:
- Alluvial soil – This type of soil is very fertile and forms major agricultural land of our country.
- Black soil – This soil has an ability to retain moisture and become sticky when wet.
- Red soil – This type of soil is highly porous, fine grained and deep.
- Leterite soil – This type of soil is found in the reason of heavy rainfall.
4. Describe the journey of a river from its source to its mouth.
Answer: The river takes birth in a mountain, becomes larger where it is meet by a number of tributaries, flows over plains and finally ends when it reaches the sea. In its early stage, it flows over steep mountains where its rate of erosion is maximum.
As the river enters into the plains, the volume of water increases and the slope of land decreases, resulting in slow speed of the river. Before meeting the sea, the river becomes large and sluggish and gets divided into several distributaries. It now comes to its old stage. The river, thus deposits silt, sand and sediments over a large area near its mouth.
5. Why is conservation of soil important? Suggest three different ways of soil conservation.
Answer: The conservation of soil is important because the formation of soil is a very slow process. It takes thousands of years to form a thin layer of soil.
The three different ways of soil conservation are:
(i) Plantation of trees.
(ii) Development and management of pasture land.
(iii) Selective agricultural practices like crop rotation and multiple cropping method.