Science - Chapter 9 - Soil
Class - 7
NCERT - Important
Questions
Short Answer Type Questions
Question 1: Explain soil and factors affecting soil.
Answer:
* Soil is the crust part of the earth. It is mainly the
mixture of rock particles and humus.
* Wind, rainfall, temperature, light and humidity are the
factors which affect the soil profile and bring changes in the soil structure.
Question 2: State the factors on which nature of soil depends?
Answer: The nature of any soil depends upon the rocks from
which it has been formed and the type of vegetation that grows in it.
Question 3: Classify soil on the basis of the proportion of particles
of various sizes.
Answer:
1. If soil contains greater proportion of big
particles it is called sandy soil.
2. If the proportion of fine particles is relatively
higher, then it is called clayey soil.
3. 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
Question 4: Define the following: (a) Soil profile (b) Horizon
Answer:
(a) A vertical section through different layers of the
soil is called the soil profile.
(b) Each layer of soil differs in feel (texture),
colour, depth and chemical composition. These layers are called horizons.
Question 5: Why is top soil known as the habitat of many living
organisms?
Answer: Soil is the
habitat for many living organisms, like bacteria, fungi, protozoan and
earthworms as it contains large amounts of nutrients. Therefore top soil is
called the habitat of many living organisms.
Question 6: Why Upper most layers in a soil profile are considered as
most productive?
Answer:
* In the soil profile, Horizon - A, also known as Topsoil is
best suited for the plant growth.
* 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.
Question 7: What is the similarity between physical and chemical
weathering.
Answer: They both reduce the size of a rock body.
Question 8: Plants help the development of the soil. How?
Answer:
* The plants attract animals, and when the animals die, their
bodies decay. Decaying matter makes the soil thick and rich. This continues
until the soil is fully formed. The soil then supports many different plants.
Question 9: Why loamy soil is known as best for growing plants?
Answer:
* The loamy soil has large amount of humus mixed in it.
* It has the right water holding capacity for the growth of
plants.
So loamy soil is known as best for growing plants.
Question 10: Explain silt .
Answer:
* 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.
Question 11: Explain the factors that help us to determine the
various types of vegetation and crops that might grow in any region.
Answer: The factors that help us to determine the various
types of vegetation and crops that might grow in any region are type of climate
and component of soil.
Question 12: What are the causes of soil erosion?
Answer: Soil erosion is mainly caused by rain, wind,
flooding, overgrazing and deforestation.
Erosion of soil is more severe in areas of little or no surface vegetation,
such as desert or bare lands
Question 13: Explain red and yellow soil.
Answer:
* 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.
Question 14: Differentiate between Clayey soil and Sandy soil.
Answer:
Clayey soil
* Higher ratio of fine particles
* Soil retains water and becomes sticky and wet
* Difficult to plough when wet
* Suitable for crops like paddy, wheat and gram
Sandy soil
* Higher ratio of large particles
* Loose particles, air permeate through the soil
* it dries up easily as it cannot retain water
* Suitable for vegetables, peanut and cotton cultivation
Question 15: List some measure to prevent soil pollution.
Answer: Minimise use of chemical fertilizers, use manures in
place of that Industrial waste should be treated before release Avoid use
polythene and plastics
Question 16. What affect the soil profile and bring changes in the
soil structure?
Answer: Soil is affected by wind, rainfall, temperature,
light and humidity. These are some important climatic factors which affect the
soil profile and bring changes in the soil structure.
Question 17. Why is top soil known as the habitat of many living
organisms?
Answer: Top soil is known as the habitat of many living
organisms because this provides shelter for many living organisms such as
worms, rodents, moles and beetles.
Question 18. Why is the topsoil important for plant growth?
Answer: Top soil is important for plant growth because it is
rich in humus and minerals which makes the soil fertile and provides nutrients
to growing plants.
Question 19. Why there is a demand to ban the polythene bags and
plastics?
Answer: Polythene bags and plastics pollute the soil. They
also kill the organisms living in the soil. That is why there is a demand to
ban the polythene bags and plastics.
Question 20. What are called horizons?
Answer: 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.
Question 21. What are the properties of loamy soil?
Answer:
Properties of loamy soil are as following:
* 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.
* The loamy soil also has humus in it.
* It has the right water holding capacity for the growth of
plants.
Question 22. What are the properties of clayey soil?
Answer: Properties of clayey soil are as follows:
* Clay particles, being much smaller, pack tightly together,
leaving little space for air.
* Water can be held in the tiny gaps between the particles of
clay. So clay soils have little air.
* They are heavy as they hold more water than the sandy soils.
Question 23. What are the properties of sandy soil?
Answer: Properties of sandy soil are:
* Sand particles are quite large.
* Sand particle cannot fit closely together, so there are
large spaces between them. These spaces are filled with air. So, the sand is
well aerated.
* Water can drain quickly through the spaces between the sand
particles. So, sandy soils tend to be light and dry.
Question 24. Why Is soil regarded as one of the most important
natural resources? Or Why is soil an inseparable part of our life?
Answer:
* Soil is one of the most important natural resources. 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.
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