BIOLOGY [3 marks Question Answer]

Bacteria and fungi present in the soil play a major role in recycling of nutrients in the soil. Plants absorb nutrients from the soil to grow. Some plants are eaten by animals. The dead remains of these plants and animals have nutrients which are broken down by the decomposing bacteria and fungi present in the soil. Thus, the nutrients are released back into the soil. These nutrients are again used by plants and recycled.

On the basis of the size of particles present in the soil and their arrangement, soil is classified into three types :
a. Clayey soil: It consists of mainly clay particles, little sand and humus. It is not suitable for plant growth due to lack of air in its particles. It has good water retaining capacity and hence gets saturated easily. It has lots of minerals also.
b. Sandy soil: It consists of mainly sand particles and a little clay. The water retaining capacity is very low and hence it does not suit plant growth.
c. Loamy soil: It contains equal amount of sand and clay. It is best suited for plants as it contains lot of humus and holds sufficient water and air spaces between soil particles.

The breaking down of huge pieces of rocks into fine particles to form soil is called weathering of rocks. It is a very slow process caused by:
a. Physical agents like wind, temperature changes.
b. Chemical agents like water.
c. Biological agents like algae, plant roots.

Different types of soils found in India are :
a. Red soil b. Black soil (Regur soil)
c. Alluvial soil d. Laterite soil
e. Desert soil f Mountain soil

Red soil :

• It is formed by the weathering of ancient rocks.
• It is rich in iron and has very little humus.
• It is porous and sandy in texture.
• It is mostly found in Kerala, Tamil Nadu,Karnataka, Odisha Telangana and Andhra Pradesh.
• It is highly fertile and suitable for variety of crops like wheat, rice and sugarcane.

Alluvial soil :

• It is formed by deposition of fine rocks by rivers.
• It is rich in humus.
• It is loamy in texture.
• It is mostly found in the plains of Haryana, Punjab, Uttar Pradesh and Bihar
• With proper fertilizers and irrigation, it is good for wheat, rice, sugarcane, cotton and pulses.