Class VII Social Science Ch-2 (DAV Publication)

                           

              

                                                 Social science

                    Class VII (DAV Publication)

      Chapter-wise questions and answers of

            Ch- 2 (The Earth and changes on it)

B. Fill in the blanks.

1. Organic matter when gets decomposed in the soil and converts it into dark coloured material is called humus.

2. Alluvial soil is found in a large part of our country.

3. I shaped and V shaped valleys are founded at the youthful stage of a river.

4. A cliff is a steep sided rock facing the sea.

5. The Ganga river and Brahmaputra river form the largest delta of the world.

C. Give a single term for each of the following statements.

1. Mounds of sand deposited by wind action in deserts.       Sand Dunes

2. The process in which a gradual wearing and carrying away of soil particles takes place on the earth’s surface.                             Erosion                           

3. The process of laying down of sediments carried by various agents of gradation.                                                                                   Deposition

4. A mass of moving ice down the slope.                                   Glacier 

5. Removal of the top layer of soil.                                             Soil Erosion

D. Answer the following questions in brief.

Q1. Specify two differences between internal and external forces.

Answer-The internal forces originate inside the earth and external forces bring about changes on the surface of the earth. Internal forces originate due to excessive heat and pressure inside the earth and express themselves in the form of volcanic eruptions and earthquakes. The external forces bring changes due to heat of sun, running water, wind action, moving ice and sea waves. These forces lead to weathering, erosion, transportation and deposition of affected materials.

Q2. Name the various agents of gradation.

Answer- Various agents of gradation are:

(i)               Running Water

(ii)            Glacier

(iii)          Wind

(iv)          Sea waves, etc.

Q3. Distinguish between transported and residual soil.

Answer- When rocks are weathered, then they are carried away by water, wind, etc and get deposited at a new place. Such soil is called transported soil. But, when the soil is formed by the weathering of a parent rock and remains present on the same site, it is called residual soil.

Q4. How is a delta formed?

Answer- Before meeting the sea, the river becomes large and sluggish as the volume of water increases and the slope of land decreases. It gets divided into several distributaries. The river, thus, deposits silt, sand and sediments over a large area near its mouth. This large deposition leads to the formation of delta.

Q5. Why is humus formed more rapidly in humid areas?

Answer- Humus is more rapidly formed in humid areas due to heavy growth of plants and rich animal life.

E. Answer the following questions.

Q1. Explain weathering. Mention the factors that affect the rate of weathering and soil erosion.

Answer- The term weathering refers to the process that breaks rock into smaller particles. It includes erosion and deposition.

The following factors affect the rate of weathering and soil erosion:

(i)               Wind

(ii)            Running water

(iii)          Glacier

(iv)          Sea waves

(v)            Temperature

(vi)          Pressure

(vii)       Rainfall   

Q2. Explain the formation of soil with the help of a labeled diagram.

Answer- After breaking the rocks into pieces due to the process of weathering, soil is formed. Two types of soil are formed

(i)               Transported Soil

(ii)            Residual Soil

                           The soil forming process continues over a long span of time. Layers after layers are formed. These layers are called horizons. The lowest horizon is called bedrock. Then horizon of weathered rocks comes which is followed by the sub soil and the top soil.

                     Diagram (See page 11 of DAV Publication textbook Social Science).

Q3. What are the major soil types found in India? Give one characteristic of each.

Answer- Major soil types found in India are:

(i)                           Black Soil- This soil, found in Deccan plateau, has an ability to retain moisture and becomes sticky when wet.

(ii)                        Red Soil- This soil is red in colour due to the presence of iron particles.

(iii)                      Alluvial Soil- It is mainly formed by the work of river and is confined to northern and coastal plains.

(iv)                      Laterite Soil- The laterite soil is found in the regions of heavy rainfall.

Q4. Describe the journey of a river from its source to its mouth.

Answer- River takes birth in a mountain or a hill becomes larger where it is met by a number of tributaries and flows over plains and finally ends when it reaches the sea.

(i)               In its early stage, the river is young. It flows over steep mountains where its rate of erosion is maximum.

(ii)            In its middle stage, it comes to the stage of maturity, here the volume of water increases and slope of land decreases, resulting in slow speed of the river.

(iii)          In its last stage, the river is said to flow through meanders. Before meeting the sea, the river becomes large and sluggish and gets divided into several distributaries. It is the old age of a river. The river deposits silt, sand and sediments over a large area near its mouth, and forms the delta.

Q5. Why is conservation of soil important? Suggest three different ways of soil conservation.

Answer- Conservation of soil is important as soil erosion affects the land all over the world. In some cases it has caused a decline in the crop yield. Soil can be conserved through appropriate measures such as plantation of trees, selective agricultural practices like crop rotation and multiple cropping method, development and management of pasture land.