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.
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