Living Science 2020 2021 for Class 7 Science Chapter 10 - Soil

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The two components of soil are as follows:

1. Humus: Humus is the dark, brown coloured component of the soil and is produced by dead remains of living things.

2. Mineral particles: Mineral particles include minerals such as potassium, calcium and magnesium. These are derived from rocks (non-living things).

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The rain water that enters into the cervices of large rocks, freezes in winters and expands. The expansion of water creates a pressure and leads to the breakdown of large rocks into small fragments, which form soil. 

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Soil made up of small particles will hold more water as compared to soil made up of bigger particles. This is because small particles pack closely which increases water retention capacity of soil. 

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The soil that is a mixture of slit, sand, clay and humus is preferred by the farmers because it is good for the growth of plants. This type of soil is called loamy soil. Loamy soil contains optimum water retention capacity as well as air trapping ability, which makes it perfect to support plant growth. 

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Weathering is a process in which large rocks are broken down into smaller fragments by the action of natural forces such as winds, water and glaciers. The smaller fragments formed by this process form soil. 

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Percolated rain water collects over the bed rock which lies just beneath the parent rock. The level of water that percolates through the soil is called water table.  

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Soil that has more sand has the ability to allow more water to percolate down. This is because the sandy soil is loose and water can easily pass through loose soil. 

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a. Wheat can be best grown in loamy as well as clayey soils.

b. In order to grow pulses, loamy soils are considered best. 

c. Cotton requires sandy-loam type of soil for its best growth. 

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We depend on the soil for the following things:

1. Food, shelter and clothing

2. Minerals

3. Water

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(a) A-horizon
Humus and the smallest particles of rock form the upper layer of soil called topsoil or A-horizon.

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(c) clay
Clay has the smallest size of particles, less than 0.002 mm in diameter. Single clay particle cannot be seen with a naked eye.

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(d) sandy loam
Sandy loam soil is best for growing cotton. It can hold air, but water can drain through it easily.

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(a) clouds
Weathering is the breaking down of huge pieces of rocks into smaller pieces by the action of natural forces such as water, glaciers, wind and roots of plants.

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(d) none of these
Water percolating into the soil collects above the bedrock. This natural level of groundwater is called the water table.

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(b) clay
Clayey soil absorbs and retains a lot of water. In clayey soil, stagnant water collects above the soil whenever it rains. This is known as water logging.

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(a) clayey soil
Paddy grows best in soils rich in clay and organic matter with a capacity to retain water.

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Breaking down of rock into smaller pieces by natural forces is called weathering.

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Clayey soil absorbs more water than sandy soil and allows less water to percolate.

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The layer of soil that contains the largest rock pieces is called C-horizon.

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The best topsoil for growing plants is loam. Loam is a mixture of sand, silt, clay and humus. It has the right water-holding capacity for plant growth.

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False.
Water logging occurs in clayey soil, which absorbs and retains a lot of water. Sandy soil cannot absorb much water because of the large spaces between the soil particles.

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Yes, soil is a natural resource because it comes from the earth and is used by us.

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False.
Although clay holds more water, water drains through soil very slowly since the particles are very small and tightly packed. This type of soil is not able to trap enough air for the roots of the plants.

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False.
A variety of dead and decaying organisms contribute to the formation of humus.

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True.
Humus makes the soil fertile by providing organic nutrients.

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True.
Humus is formed by the action of decomposers such as bacteria and fungi.

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Soil consists of two components:
(a) Small mineral particles which come from larger rocks. These minerals include salts of iron, calcium, potassium, magnesium, phosphorus, etc.
(b) Humus is dark brown in colour and consists of decaying remains of plants and animals.

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Weathering is a process by which huge pieces of rocks break down into smaller pieces and gradually change into soil. It takes place by the action of natural forces such as water, wind, roots of plants and variations in day and night temperatures.

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Sandy soil will allow more water to percolate because it has a lot of sand and water drains quickly through large spaces between the sand particles.

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Clayey soil will absorb more water because the soil particles are very small and the water drains very slowly.

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Humus is a component of soil which is dark brown in colour and consists of decaying remains of plants and animals. When small plants such as mosses, lichens and ferns die, they mix with the soil and form humus. Humus makes the soil fertile by providing organic nutrients.

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Due to large variation in day and night temperatures, the rocks expand during the day and contract during the night. This constant expansion and contraction weakens the rocks and they crack and crumble causing weathering.

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The natural level of groundwater is called the water table. Rainwater percolates through the soil and collects above the bedrock to form the water table.

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The role of water in the formation of soil is extremely important in the following ways:
(a) Rainwater which enters rock crevices freezes in winter. As a result, it expands. This expansion puts pressure on rocks and breaks the rocks into smaller pieces.
(b) The small pieces of rocks roll down by the force of flowing water. They collide against the ground and against each other. Hence, they break down further and get converted into very fine particles.

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Roots of trees growing through rocks exert great pressure on the rocks. This pressure causes cracks in the rocks, leading to the formation of soil. The roots of trees bind to the soil and prevent soil erosion and provide protection to the soil.

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The different layers of soil are as follows:
(i) Topsoil (A-horizon):
It consists of humus and the smallest particles of rock.
(ii) Subsoil (B-horizon):
It consists of small pieces of rocks and some nutrients such as soluble minerals and iron oxides.
(iii) Parent rock (C-horizon):
It consists of small pieces of rocks with cracks and crevices.

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Answer:

Loam is a mixture of sand, silt, clay and humus.
It is considered to be the best topsoil for growing plants because it has the right water-holding capacity for plant growth. It also has adequate spaces between the soil particles to trap air required by the roots of plants.

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Soil is considered as our most important natural resource due to the following reasons:
(a) It provides us food, clothing and shelter: By supporting growth of plants, the soil provides us with food and clothing. Plants also provide us with wood, which is used for constructing house.
(b) It provides us minerals: Minerals are dug out from the earth to extract metals such as iron, gold, silver, etc.
(c) It provides us water: Water that seeps into the soil is stored underground as subsoil water. This water is used for drinking and other purposes.

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Earthworms improve the soil texture. They make the soil loose by burrowing into the soil, thus allowing air to enter into it and water to drain from it. They also form channels in the soil for roots to spread through. Hence, earthworms are referred to as 'farmer's friend'.

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The rate of water percolation through the soil decreases as a result of construction of buildings and roads because water cannot percolate into cement. Due to this, the water table will shrink.

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Topsoil is the most fertile soil because it consists of humus. Soil erosion removes topsoil, thus decreasing soil fertility. The formation of topsoil by the process of weathering takes a very long time. Hence, we are so concerned about soil erosion.

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Humus is formed by the death and decay of plants and animals. When small plants die, they mix with the soil to form humus. These plants and animals are confined to topsoil. Hence, topsoil have much more humus than subsoil.

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Clayey soil is most suitable for making toys because it does not crumble when rolled into a ball.

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The Gorge which has been formed due to weathering is a result of change in weather conditions over a period of time.
In winters, the water seeps into the crevices of rocks and as the water freezes it expands and turns into ice. This expansion causes the cracks to become wider and deeper and as a result of this erosion of small stones occurs. 
During rainy seasons, heavy rains causes water to rush down the cracks, further eroding the rocks and stones. As these, rocks crumble and fall away, they cause the widening of the gorge.
This weathering phenomenon has and resulted in the formation of gorge in the Grand Canyon.

Answer:

It shows that Rahul is a concerned and aware citizen. He is very much aware of the fact that biodegradable garbage can be used to produce compost. He uses this information in his daily life. He knows how to contribute in solving the growing menace of waste.