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Karnataka State Syllabus Class 7 Science Chapter 9 Soil
Class 7 Science Soil NCERT Textbook Questions and Answers
Tick the most suitable answer the question 1 and 2.
In addition to the rock particles, the soil contains.
i. air and water
ii. water and plants
iii. minerals, organic matter, air and water
iv. water, air and plants.
iii. minerals, organic matter, air and water
The water holding capacity is the highest in
i. sandy soil
ii. clayey soil
iii. loamy soil
iv. mixture of sand and loam.
ii clayey soil
Match the items in Column I with those in Column II
|Column I||Column II|
|i. A home for living organisms||a. Large particles|
|ii. Upper layer of the soil||b. All kinds of soil|
|iii. Sandy soil||c. Dark in colour|
|iv. Middle layer of the soil||d. Small particles and packed tight|
|v. Clayey soil||e. Lesser amount of humus|
i – b,
ii – c,
iii – a,
iv – e,
v – d
Explain how soil is formed.
Soil is formed through the process of weathering.
Weathering is a process of physical break-down 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 the soil.
How is clayey soil useful for crops?
Following are the properties of clayey soil:
- It has very good water holding capacity.
- It is 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 soil having these characteristics are useful for such kind of crops.
List the difference between clayey soil and sandy soil.
|Clayey soil.||Sandy soil.|
|1. Ratio of fine particles is higher.||1. Ratio of large particles is higher.|
|2. Soil retains water and becomes sticky and wet.||2. Loose particles, air permeate through the soil.|
|3. Suitable for crops like paddy, wheat and gram.||3. Suitable for vegetables, peanuts and cotton cultivation.|
|4. Difficult to plough when wet.||4. Dries up easily cannot retain water.|
|5. It is heavy in weight.||5. It is light in weight.|
|6. Less air is trapped between the particles.||6. More air is trapped between the particles.|
Sketch the cross-section of soil and label the various layers.
A Vertical section through different layers of the soil is called the soil profile. Each layer differs in feel (texture) colour, depth, and chemical composition. These layers are referred to as horizons.
Razia conducted and experiment in the field related to the rate of percolation. She observed that it took 40 min for 200 mL of water to percolate through the soil sample. Calculate the rate of percolation.
Amount of water = 200 mL
Percolation time = 40 min.
Explain how soil pollution and soil erosion could be prevented.
Prevention of soil Pollution
- Use manures instead of chemical fertilizers.
- Industrial Waste should be treated before release.
- Avoid the use of polythene and plastic or they should not get mixed in the soil.
Prevention of soil erosion
- Afforestation large scale planting in place of cut down forests.
- Avoiding overgrazing of grasslands.
- Use of step – farming in hill regions.
Solve the following crossword puzzle with the clues given.
2. Plantation prevents it.
5. Use should be banned to avoid soil pollution.
6. Type of soil used for making pottery.
7. Living organisms in the soil.
1. In desert, soil erosion occurs through.
3. Clay and loam are suitable for cereals like.
4. This type of soil can hold very little water.
5. Collective name for layers of soil.
Class 7 Science Soil Additional Important Questions and Answers
What is Soil? What are its uses?
Breaking down of rocks by the action of wind, water and climate causes the formation of soil The nature of Soil depends upon the rocks from which it has been formed and the type of vegetation that grows in it. The Soil is covered on the top surface of the earth. The mixture of rock particles and humus is called the soil. The uses of soil are many. It provides anchorage to the plants. It is home for many organisms. It supplies water and nutrients to the plants. It is essential for agriculture.
The rotting dead matter in the soil is called humus.
Define the Soil profile with the figure.
A Vertical section through different layers of the soil is called the Soil profile. The layers of the Soil are referred to as horizons.
The uppermost horizon is very fertile and provides nutrients to plants. It is a top-soil or A – horizon. The Second layer below this is B-horizon. The third layer is C-horizon below this bedrock which is hard and difficult to dig.
What are the Different Varieties of Soil?
There are 3 different varieties of Soil.
- Sandy Soil.
- Clayey soil and
- Loamy soil.
Define loamy Soil & its uses.
The best topsoil for growing plants is loam. Loamy Soil is a mixture of sand, clay, and another type of soil particle known as silt. Silt occurs as a deposit in river beds. The size of the silt particles is between those of sand and clay. The loamy soil also has humus in it. It has the right water holding capacity for the growth of plants.
What is percolation? How do you find out the percolation rate of water in the Soil?
The property of Soil to allow the water to filter though it is called percolation.
The percolation rate can be calculated by the amount of water that should be divided by the time taken to percolation, for eg: 1 kg of soil is taken in a pot or bucket. Put 300 ml of water, if it took 10 minutes to percolete. We can calculate the rate of percolation by using the formula
Percolation rate (ml/min) amount of water 300 ml
What is meant by alluvial soil? What are its uses?
Rivers of north India which flow from the Himalayas bring a variety of materials including Silt, clay, sand, and gravel. They deposit their materials called alluvial Soil, this Soil is very fertile and grow many crops and give a very good yield.
How do you find out the absorption of water by soil?
Take a plastic funnel. Take a filter paper (or a piece of newspaper sheet), fold, and place it as shown in the figure. Weigh 50g of dry, powdered soil and pour it into the funnel. Measure a certain amount of water in a measuring cylinder and pour it drop by drop on the soil. You can use a dropper for this purpose. Do not let all the waterfall at one spot.
Pour water all over the soil. Keep pouring water till it starts dripping. Subtract the amount of water left in the measuring cylinder from the amount you started with. This is the amount of water retained by the soil. Record your results in your notebook in the following manner:
Weight of soil = 50g
The initial volume of water in the measuring cylinder = U mL
The final volume of water in the measuring cylinder = V mL
The volume of water absorbed by the soil = (U – V)mL
Weight of water absorbed by the soil = (U – V) g
(1 mL of water has a weight equal to 1 g)
percentage of water absorbed
Draw a neat diagram and label the parts of removing moisture from the soil.
Match the following :
|1. Clayey Soil||1. Paddy, Wheat etc.|
|2. Alluvial Soil||2. Pots, Statues, Playthings|
|3. Loamy & Sand mixed Soil||3. Weathering|
|4. Clay||4. Wheat, Grams|
|5. Sand||5. Cotton|
|6. Wind, Water, Climatic factors are causes of||6. Water and drain quickly|
1 – d,
2 – a,
3 – e,
4 – b,
5 – f,
6 – c
How Soil can be classified? Name them.
The Soil is classified on the basis of the proportion of particles of various sizes. If the soil contains a greater proportion of big particles. It is Sandy soil. If the proportion of fine particles is relatively higher then it is clayey soil. The best topsoil for growing plants is loamy soil.
What is meant by Weathering?
The process of breaking down rocks into the soil by wind, water, and climate is called weathering.
II. Fill in the blanks :
- The earthy fragrance of soil after the first rain is always refreshing.
- Soil is composed of distinct layers.
- A vertical section through different layers of the soil is called the Soil profile.
- The Soil layers are referred to as horizons.
- Below the C-horizon, the layer is the bedrock which is hard and difficult to dig with a spade.
- The mixture of rock particles and humus is called the Soil.