Page 105 - ACTIVE SCIENCE 4 TOC

• The roots of plants break rocks into smaller pieces. These rock pieces are further
broken down into smaller particles and are called sand.

• Soil is the topmost layer of the earth’s surface. It is made of sand, silt and clay
besides organic humus.

• Sand, silt and clay are small particles of rock which are formed by weathering.
• There are many living things in the soil like earthworms and micro-organisms, which

help in the development of humus.
• Soil is classified into three types based on its size, feel and colour of particles. These

are sandy soil, clayey soil and loamy soil.
• The removal of the topsoil by various natural forces and human activities is called

soil erosion.
• Crop rotation is the practice of cultivating different types of crops on the same

farmland in successive seasons. This process makes the soil fertile.

Glossary

• Topsoil : The uppermost layer of the soil.

• Subsoil : The middle layer of the soil.
• Bedrock : The bottom layer of the soil.
• Crop rotation : Growing different types of crops on the same farmland.

• Soil conservation : Prevention of erosion of soil.

• Soil erosion : The removal of topsoil by the action of either wind or water.

Practice Time

A. Tick the correct option.
1. The process of natural breakdown of rocks is called _____________.

a. weathering b. soil erosion

c. crop rotation d. soil conservation
2. The uppermost layer of soil is called _____________.

a. topsoil b. bedrock
c. subsoil d. soil profile

3. This layer contains large pieces of rocks and is very hard. It is called _____________.
a. topsoil b. subsoil

c. bedrock d. humus

112 Active Science-4