Science 2 Marks Questions

Physical weathering is the breakdown of rock into smaller particles due to factors such as freezing and thawing, release of pressure, water absorption, salt crystal formation, land mass uplift, expansion and contraction from the sun or fire, plant root growth, actions of animals, abrasion, or other means that do not directly affect the rock's chemistry. It is also called mechanical weathering.

Alluvial Soils are mainly found in the plains of northern India. These soils have low phosphorous and nitrogen content and found in the north western regions of the country but Mountain soils are considered as a significant variety of soil in the Himalayan region of the country. They are mainly found in dry and cold district in the northern region of India.

Soil consists of:

• soil particles of different sizes
• soil water
• humus
• soil air
• flora and fauna

Chemical weathering is the dissolution, carbonation, oxidation, or hydrolysis of rock and mineral by chemical means only, mostly from reactions with water or the acids contained in rainwater. Other materials are formed in the process. Warm, tropical climates are ideal environments for chemical weathering to take place as the chemical reactions are quickened by the bountiful rain and warm temperatures.

The farmer can convert acidic soil into neutral soil by adding a small quantify of quicklime or slaked lime solution to the soil. Quick lime and slaked lime are bases and hence, react with the excess acid present in the soil and reduce its acidity.

Silt is the soil present as deposits in riverbeds. It is formed by the weathering of rocks in the mountains and flows into the rivers. It is a component of loamy soil which is considered most suitable for growth of plants.

In the soil profile, Horizon-A, also known as Topsoil is best suited for the plant growth. As we know that availability of nutrients and water in soil helps to determine the productivity of soil. Top soil is rich in humus minerals along with water. Thus, Top soil is considered as more productive.

1. A vertical section through different layers of the soil is called the soil profile.
2. Each layer of soil differs in feel (texture), colour, depth and chemical composition. These layers are called horizons.

1. It enables easy root growth.
2. For easier percolation of water.
3. For aerating the soil enabling air to get into deeper layers of soil.
4. For removing the weeds.

A non-living organic matter formed from remains of dead and decay plants and animal by the activity of microorganism present in soil. Humus controls and regulates many soil functions, as well as plant growth. The better the humus content in the soil the healthier and more productive soil will be. Good humus count in soil will hold soil moisture longer, thus lesser water is required for crop production, also god humus count reduces wind erosion of soil.

1. Decrease in soil fertility and thus crop productivity.
2. Water bodies become muddy, affecting aquatic life.

The terms for the above described statements are as follows:

1. Weathering
2. Soil erosion
3. Soil pollution
4. Percolation

Earthworms burrow through the soil, ants live in large colonies and burrows in soil, centipedes live under stones and in soil, some bacteria living in soil fix nitrogen for the plant to take up and microorganisms decompose dead plants and animals.

Percolation refers to the amount of water seeping down while amount of water rationed refers to the amount of water held. Higher percolation means large spaces between soil particles and lower in the amount of water retained.

Deserts are made up of sand, thus when the rainwater falls on land, it percolates immediately downwards in the spaces between sand particles. So, the streams of water in desert region are not visible even during rainy season.

Clayey soil is useful for the crops because:

• It has good water retaining capacity.
• It is rich in humus.
• It is fertile in nature.

Crops like wheat and rice can be easily grown in clayey soil.