Science 5 Marks Questions

Strong wind and rain can cause soil erosion from the barren land. This can be shown by performing an activity.
Take a wooden block and place some soil or sand on it. Keep an ice-cube tray at one end of the wooden black. Take a small battery-operated fan or hair dryer and hold it at the other end of the black near sand so that it blows the sand into the tray.
We will observe that when the fan blows it causes sand or soil particles to move and these get land in the various compartment of the ice-cube tray. This activity shows that the wind blows the soil on a barren land and may cause soil erosion.

Following are the different types of soil found in India:

1. Laterite Soils: This typical soil is found in those regions which receive heavy rainfall. This soil is poor in lime content and hence it is more acidic. This soil contains least moisture content.It is basically red in colour because of the presence of iron oxides. It is more popular in the coastal regions of Ratnagiri District and Malabar.
2. Black Soil: It is black in colour due to presence of salt and large amount of humus. This soil becomes sticky when is wet. It does not contain adequate nitrogen but it contains sufficient phosphorous required for the growth of the plants.It is generally found in hilly areas.
3. Red and Yellow Soils: Red and yellow soils are found in areas, which receive low rainfall. They contain huge concentration of iron oxides that are responsible for giving the reddish or yellow colour.
4. Alluvial Soils: 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.
5. Mountain Soils: 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.

The main agents of weathering are:

1. Temperature: Temperature changes that cause the rock surface to break apart.
2. Frost: Ice expands and produces pressure, causing the crevices in rock to open.
3. Air: Wind blow across rock surface and carry minute particle and form layer.
4. Water: Continuous movement of rain water causes braking down of rock particles into fine particles.
5. Living organism: Lichen grow on the surface of rocks and produce acid which corrode the rocky surface. Weathering by living organism is called biological weathering.

Soil is one of the most important natural resources. It is the uppermost layer of earth’s crust which is blackish-brown in colour. Major functions of the soil are:

1. It supports plant growth by holding the roots firmly and supplying water and nutrients to the plants.
2. It acts as a natural habitat for many organisms like earthworm, fungi, bacteria, ants, etc.
3. It is also essential for agriculture which provides us food, clothing and shelter for all.
4. It supplies water and nutrients to plants.

Therefore, we can say that the soil is inseparable part of our life.

There are many ways to prevent soil erosion:

1. By planting more trees and increasing the vegetation cover.
2. By prevented Cutting of trees and deforestation and taking efforts to increase the green areas.
3. By maintaining soil in its natural condition by using less manure or by crop rotation.
4. By arranging proper irrigation.

Different layers of the soil are referred to as horizons:

• The uppermost layer, the top soil, also known as A-horizon is generally dark in colour and fertile as it is rich in humus and minerals. This layer is generally soft, porous and can retain more water. This provides shelter for many living organisms such as worms, rodents, moles and beetles. The roots of small plants are embedded entirely in the topsoil.
• The next layer, middle layer called B-horizon has a lesser amount of humus but more of minerals. This layer is generally harder and more compact.
• The third layer is the C-horizon which is made up of small lumps of rocks with cracks and crevices.
• Below this layer is the bedrock, which is hard and difficult to dig with a spade. Water can be held in the tiny gaps.

The borewells have to be dug very deep in towns and cities to get water as compared to those in villages because:

1. Excessive use of water in towns, depletes the groundwater.
2. Towns and cities have asphalted roads and vast areas of soil are concreted.

As a result, rainwater cannot percolate to recharge groundwater and the groundwater level further decreases.
Villages have larger areas of open soil surface and fewer asphalted roads and concrete surfaces. Thus, larger soil surface area is available for rainwater to percolate into the soil easily and recharge the groundwater. As a result, even shallow borewells yield water.

Soil is one of the most important natural resources because:

• It supports the growth of plants by holding the roots firmly and supplying water and nutrients.
• It is the home for many organisms.
• Soil is essential for agriculture. Agriculture provides food, clothing and shelter for all.
• Soil is thus an inseparable part of our life.

The contamination of soil due to excess use of chemicals and harmful waste products like fertilizers, insecticides, industry waste is called soil pollution.The causes of soil pollution are as follow:

• Excessive use of chemicals fertilizers and pesticides Acid rain.
• Dumping of waste materials.
• Leakage of radio hazard materials.
• Polythene and plastics pollute soil as well as kill the organisms living in soil.

The soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering. There are two different types of weathering. Physical weathering and chemical weathering. Mechanical (physical) weathering is the breakdown of rock into smaller particles due to such factors 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. 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.

Laterite soil is found in those regions which receive heavy rainfall. This soil is poor in lime content and hence it is more acidic. This soil contains least moisture content. It is basically red in colour because of the presence of iron oxides. It is more popular in the coastal regions of Ratnagiri District and Malabar. But Black Soil is black in colour due to presence of salt and large amount of humus. This soil becomes sticky when is wet. It does not contain adequate nitrogen but it contains sufficient phosphorous required for the growth of the plants. It is generally found in hilly areas.

The soil is formed by the breaking down of rocks by the action of wind, water and climate. This process is called weathering, it broke down soil into small pieces that get mixed with humus and form soil. There are two different types of weathering. Physical weathering and chemical weathering. Mechanical (physical) weathering is the breakdown of rock into smaller particles due to such factors 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. 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.