Science 3 Marks Question

No, it is not a good practice to remove grass and small plants growing in an open, unused field because the plants cover the soil surface. Their roots bind the soil particles, holding and adhering them in place. It helps in preventing the topsoil from being washed off during heavy rain, floods and winds. In this way, soil erosion is prevented and top soil layer is preserved for growing more plants.

Due to the very small size of the particles of clayey soil, particles are packed tightly and therefore can retain water. Clayey soil is also rich in organic matter. For growing crops such as wheat, gram, and paddy, the soil that is good at retaining water and rich in organic matter is suitable. Therefore, clayey soils having these characteristics are useful for such kind of crops.

There are three different types of soil:

1. Sandy soil containing sand particles in them.
2. Clayey soil contains clay particles with small amount of humus in it. It is a fertile soil.
3. Loamy soil is a mixture of sand, clay silt and humus. It is a fertile soil.

Soil is formed through the process of weathering. Weathering is a process of physical breakdown and chemical decomposition of rocks and minerals near or at the surface of the earth. This physical and chemical decomposition is primarily done by wind, water, and climate. As a result of these processes, large rock pieces are converted into smaller pieces and eventually to soil.

• If soil contains greater proportion of big particles it is called sandy soil.
• If the proportion of fine particles is relatively higher, then it is called clayey soil.
• If the amount of large and fine particles is about the same, then the soil is called loamy.

Thus, the soil can be classified as sandy, clayey and loamy.

In dense forests, the tree cover (canopy) prevents rainwater from, directly falling on the ground/soil. Also, the roots of vegetation bind the soil particles and hold them together. As a result, soil erosion is minimised. But in barren open fields, the soil is exposed to the failing rain. The soil particles become loose due to the impact of raindrops and the flow of water carries them away. The flowing water further erodes the soil surface aggravating erosion.

1. An earthworm helps in making the rich humus in soil.
2. Ant, earthworm, termites, milipede, centipede, etc.
3. Curiosity to learn and scientific attitude.

Prevention of soil pollution: The persistent build-up of toxic compounds in the soil is defined as soil pollution. To prevent soil pollution, its causes must be controlled.

• Plastics and polythene bags destroy the fertility of soil. Hence, they should be disposed properly and if possible, their use should be avoided.
• Some waste products from industries and homes pollute soil. These pollutants should be treated chemically to make them harmless before they are disposed.
• Other pollutants of soil include pesticides and insecticides. Therefore, excessive use of these substances should be avoided.

Prevention of soil erosion: Removal of the upper fertile layer of the soil (top soil) by strong wind and flowing water is known as soil erosion. Roots of plants bind the soil firmly and prevent soil erosion. Absence of plants leads to soil erosion. Therefore, soil erosion can be prevented by planting trees and checking indiscriminate cutting of trees.

1. Gravel is the heaviest rock material.
2. Humus is the lightest soil component which floats on the water surface.
3. The soil component forms various layer one above the other according to the size of soil particle.

Yes, soil erosion does not occur easily where the land is covered by vegetation (trees and other plants). It occurs easily in those areas of land which are not covered by vegetation (trees and other plants) or have very little vegetation. If there is vegetation on land,

• Then the roots of vegetation growing in the soil bind the particles of topsoil firmly. Due to this, the blowing wind and flowing rainwater are not able to carry away topsoil and hence soil erosion does not occur.
• Then much of the falling rain hits the trees and plants before it hits the soil. In this way, the cover of vegetation softens the effect of heavy rains on the soil.

Roots although underground possesses living cells that require oxygen for respiration and production of energy. They absorb oxygen that is present in the spaces between soil particles. But in water-logged soils, water occupies spaces between soil particles and pushes the oxygen out into the atmosphere. Thus, roots are deprived of oxygen and this affects the plant growth.

Raw soil differs from baked soil. The raw soil is white or dull blackish coloured soil. It contains water and air in it and can be moulded. Baked soil is the heated raw soil which lost its water molecule due to heating and becomes red. Once the soil gets heated, it cannot be moulded into other form. Clay soil is used for making matkas, toys, pots, etc. The soil is kneaded along with horse dung to make best quality of raw clay soil. This kneaded soil is then placed on the wheel and appropriate shape is given. The final shape of the material is given with hands. The pots and matkas are then kept for drying for three days. These items are baked at high temperature after drying in air and then coloured.

Different particles of soil have different sizes which affect its properties like:

• Sand particles are quite large and having large spaces between them. These spaces are filled with air. Water can drain quickly through these spaces. So, sandy soils tend to be light, well aerated and rather dry.
• Clay particles, being much smaller, pack tightly together, leaving little space for air. So, clay soils have little air. But they are heavy as they hold more water than the sandy soils.
• Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the good water holding capacity for the growth of plants.

1. The various important component of soil are air, water, rock particles, minerals, humus and living organisms like bacteria, fungi, worms (earthworm), rodents, insects (ant and beetle), etc.
2. The increasing order of rock particles are,

Clay → Silt → Sand → Gravel

3. The figure shows waste material like polythene bags, plastics, glass and metal objects are dumped which causes soil pollution.

1. It is because these substances pollute the soil. They also kill the organisms living in the soil.
2. Substances which pollute the soil are a number of waste products, chemicals, pesticides, polythene bags and plastics.
3. Alertness, responsibility and ecofriendly nature.

1. Loamy soil is a mixture of sand, clay and another type of soil particle known as silt. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the good water holding capacity for the growth of plants.
2. If soil contains greater proportion of big particles it is called sandy soil.in sandy soil Sand particles are quite large and having large spaces between them. These spaces are filled with air. Water can drain quickly through these spaces. So, sandy soils tend to be light, well aerated and rather dry.

The contamination of soil with waste materials especially used polythene bags and plastics, pesticides, fertilisers, acid rain industrial chemical wastes, etc., is called soil pollution. Pesticides are the poisonous chemical substances which are sprayed on standing crops to save them from the harmful insects and diseases. Some of these pesticides also mix up with the soil in the fields and pollute it. The grains, fruits and vegetables grown in this polluted soil contain pesticides. When we eat such contaminated grains, fruits or vegetables, the pesticides present in them damage our health also.