Page 64 - Ripples SCIENCE 7 - TEJPUR Edition 2024 Answer Key

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7 Soil

Chapter in a Nutshell

v Soil is a mixture of minerals, sand, air, water, etc.
v It is the most important natural resource.
v Soil is essential for the growth of plants.

v Different types of soil are found in different parts of India. Soil can be clayey, loamy or sandy.
v Soil is formed by the breaking down of rocks into tiny particles by the action of the Sun,

wind, temperature and rain. This process is called weathering.
v Humus is the organic matter formed as a result of decomposition of dead plants and animals

by various microorganisms.
v When rocks break down into smaller particles by various physical factors, such as temperature,

wind, water, etc., but their chemical properties do not change, then it is known as physical
weathering.
v During chemical weathering, changes occur in the chemical composition of rocks.

v The process of weathering caused due to plants and animals is called biological weathering.
v The vertical section through soil showing its different layers is called the soil profile.

v Each layer differs in feel (texture), colour, depth and chemical composition. These layers are
referred to as horizons.
v A-horizon or the topsoil is the topmost layer of the soil. It is very soft and porous. It contains

large amounts of humus and minerals and can retain water easily.
v B-horizon lies beneath the top soil. It does not contain humus but minerals are found here

in large quantities.
v C-horizon is the third layer of the soil which consists of small rocks with cracks in them.

v Below C-horizon is the bedrock. This is the last layer of the soil. It contains huge rocks that
are not weathered as they are not exposed to sunlight or wind.

v Soil is classified as: sandy soil, clayey soil, loamy soil and silt soil.
v Soil is composed of both biotic and abiotic material such as air, water, mineral, plants and
animal matter.

v Percolation rate of water is the property of absorption of water by soil.
v Percolation can be defined as the property of the soil by which it allows water to flow

through it.
v The percolation rate of water depends on the type of soil. It is the least in clayey soil and the

highest in sandy soil.

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