Soil

16. SOIL

SOIL

points to remember :

1. Soil :

(1) Soil provides support and nourishment to plants.

(2) Soil helps plants to grow. It is the base of agriculture.

(3) The survival of all plants and animals and their nourishment

depends upon the soil.

2. Constituents of soil :

Stones, pebbles, sand, fine soil particles and organic substances

are the various constituents of soil.

3. Formation of soil – weathering of rocks :

The process by which rocks are transformed into soil is called

weathering.

(1) The weathering of rocks and formation of soil are affected by

various elements of nature.

(2) Changes in the atmospheric heat and cold, winds, etc. bring

about the weathering of rocks.

(3) The weathering of rocks and boulders also occur due to the

effects of rivers, rainwater, winds and continuous changes in

the weather. Owing to this, rocks and boulders are converted

into smaller particles which ultimately form soil.

4. Biological weathering of rocks :

(1) Rodents like rats and bandicoots that live in burrows help in

the conversion of rough earth into soil.

(2) Roots of the plants growing into the cracks in rocks play an

important role in the weathering of rocks. The soil formed is

generally clay.

5. It takes about 800 to 1000 years for the formation of a 2.5 cm thick

layer of fertile soil.

6. Soil – a natural resource :

(1) Plant life has developed on the earth owing to the presence of

soil.

(2) Plants provide food to animals and human beings.

(3) Plants meet our three basic needs – food, shelter and

clothing.

(4) Minerals and metals are also obtained from the soil.

7. Uses of soil :

(1) Soil can be given any desired shape. This property of the

soil is called plasticity.

(2) Soil nurtures plants.

(3) Soil holds water.

(4) Bricks that are used for construction work are made from

the soil.

(5) The earthen vessels and walls of some houses are made of

clay (soil).

8. Colour of the soil :

(1) The soil has different colours. It may be red, black, yellow

and copper coloured.

(2) The colour of the soil gives an idea of its fertility, drainage

and other such properties.

(3) The colour of the soil depends upon the following

constituents.

(i) Texture (ii) Organic content and (iii) Chemical

substances like iron, quicklime, etc.

9. Soil also contains fine particles of quartz, felspar, mica,

carbonates of metals, oxides and sulphides of iron along with

the organic matter.

10. Types of soil

(1) There are three types of soil, viz., China clay, clay and

loamy soil.

(2) The China clay or Kaolin is found near the Kaolin mountain

in China.

(3) It is white in colour and is used for making crockery, tiles

for bathrooms and laboratory apparatus.

(4) Different kinds of oxides are used to decorate earthenwares

or porcelain articles. For example, iron oxide is used to

obtain red colour while copper oxide is used to obtain green

colour.

(5) Loamy soil being white in colour is used to make idols and

statues.

11. Types of soil : (According to texture)

(1) The size of soil particles decides the texture of the soil.

 (2) There are three types of soils based on the texture. These

are sandy soil, clayey soil and silt.

(3) Sandy soil has greater proportion of sand. It has the least

capacity for holding water.

(4) Clayey soil has greatest proportion of fine particles. It has

the greatest capacity for holding water.

(5) Silt soil consists of fine to medium sized soil particles. It has

medium capacity for holding water.

(6) The soil which holds lots of water is not well aerated.

12. Constituents of soil :

(1) Soil has constituents of both plant and animal origin. These

constituents are called organic constituents.

(2) Constituents of plant origin include bacteria, algae, fungi,

decomposed leaves of plants, etc.

(3) Constituents of animal origin constitute protozoa, worms,

insects, shells and decomposed remains of dead animals.

13. Soil erosion :

(1) The removal of top fertile layer of the soil from the soil

surface is called soil erosion.

(2) Soil is eroded by rainwater falling on it and by fast currents

of water flowing on it.

(3) Soil is also eroded by gusts of winds.

(4) Soil must be kept covered to prevent soil erosion. Growing

grass and the crops on the land, cover the soil.

(5) Trees planted on the land also provide the cover.

(6) Soil erosion can be reduced by arranging the soil

horizontally across the lines of slopes as erosion of soil

depends upon the slope.

(7) Construction of bunds to stop the flowing water also

prevents the soil erosion.

14. Soil Conservation :

(1) Arresting soil erosion to conserve the soil is called soil

conservation.

(2) The government has set up soil conservation department at

every district place. One can get information about how to

reduce soil erosion at this place.

15. Social forestry :

(1) Planting of trees on the borders of fields on the sides of

roads and railway tracks and on the banks of rivers and

streams is called social forestry.

(2) The Government of India, in the year 1976, started social

forestry projects for the benefit of the people.

(3) The project motivated the people to start planting of trees

in all possible places.

(4) This project encourages small farmers and adivasis to plant

trees. It provides financial assistance to them for this

purpose.

16. Soil pollution :

(1) A disturbance in the natural balance of various

constituents of soil is called soil pollution.

(2) Chemical fertilizers, pesticides, industrial effluents, etc.

pollute the soil.

(3) Crops do not grow well on polluted soil.

(4) Soil pollution can be prevented by using organic fertilizers

instead of chemical fertilizers.

(5) Overuse of fertilizers and pesticides should also be avoided

for the prevention of the soil pollution.

17. Soil testing :

(1) Soil testing is done to find out the quality of the soil.

(2) Soil testing helps us to find out the colour, texture and the

constituents of organic matter in the soil.

1 Answer the following questions :

* (1) What is soil made of ?

Ans. Soil is made of stones, pebbles, sand, fine soil particles

and organic substances.

(2) How do rocks break?

Ans. (1) Changes in the atmosphere affect the rocks. Owing to

changes in atmospheric heat and cold, rocks develop cracks. Cracks

are also formed due to extreme heat and cold. (2) The cracks that

develop in rocks store water which freezes in the cold. Freezing

water increases in volume and causes the breaking of rocks.

(3) What is weathering ? How does it occur ?

Ans. (1) The process by which rocks are transformed into soil

is called weathering. (2) The weathering of rocks converts them

into smaller and smaller particles which eventually form the soil.

(3) The various elements of nature such as rivers, rainwater,

winds and continuous changes in weather cause weathering.

(4) Rodents like rats and bandicoots make burrows in the soil.

Owing to this rough earth gets converted into the soil. This

biological process goes on in the ground continuously and causes

weathering.

(4) State the various uses of soil.

Ans. The various uses of soil are as follows : (1) Soil nurtures

the plants. (2) Soil has a capacity to hold water. Owing to this

property of the soil, water is available to us all the year from deep

ponds and wells where it is collected naturally. (3) Bricks that are

used for construction work are made from the soil. (4) Vessels of

everyday use are made from the soil. (5) The idols and statues are

also made from the soil.

(5) What are the different colours of the soil ? Name the

constituents on which the colour of the soil is dependent.

Ans. 1. Colour of the soil : The different colours of the soil

are as follows : (1) Black (2) Red (3) Yellow (4) Copper.

2. Constituents on which the colour of the soil is

dependent :

(1) Texture of soil (2) Organic content of soil (3) Chemical

substances like iron and quick lime.

(6) What are the two main constituents of the soil ?

Ans. (1) The soil has two main constituents viz., constituents

of plant origin and constituents of animal origin. Both these

constituents are called organic constituents. (2) Bacteria, algae,

fungi, decomposed leaves of plants, etc. are the constituents of plant

origin. (3) The constituents of animal origin include protozoa,

worms, insects, shells and the decomposed remains of dead

animals.

 (7) What are the three types of soil which are used for

making earthen pots and other artifacts? What are their

special features ?

Ans. (1) China clay, clay and loamy soil are the three types of

soil which are used for making earthen pots and other artifacts.

(2) The soil which is found near Kaolin mountain in China is called

China clay or Kaolin. It is white in colour and is used to make

crockery, tiles of bathrooms, laboratory apparatus, etc.

(3) Different kinds of oxides are mixed to China clay to decorate

earthenware or porcelain articles. Iron oxide is mixed to obtain red

colour while copper oxide is mixed to obtain green colour.

(4) Loamy soil being white in colour is used to make idols and

statues.

(8) What determines the texture of soil ? What are the

different types of soil based on its texture ?

Ans. (1) The proportion of soil particles of different sizes

determines the texture of soil. (2) There are three different types of

soil based on its texture. These are sandy soil, clayey soil and silt.

(3) The sandy soil contains greater proportion of sand. It has the

least capacity for holding water. (4) Clayey soil has the greatest

proportion of fine particles called clay. It has the greatest capacity

for holding water. (5) Silt soil consists of fine to medium-sized soil

particles. It has medium capacity for holding water.

(9) What is soil erosion ? What are the three causes of soil

erosion? Write the effects of soil erosion.

Ans. 1. Soil erosion : The removal of top fertile layer of the

soil from the soil surface is called soil erosion.

2. Causes of soil erosion : The causes of soil erosion are as

follows : (i) Rainwater falling on the soil. (ii) Fast currents of

water flowing on the soil. (iii) Gusts of the wind.

3. Effects of soil erosion : (i) Soil cover is reduced. (ii) Loss

in fertility of the soil.

* (10) What steps can be taken to prevent soil erosion ?

Ans. The following steps can be taken to prevent soil erosion :

(1) Soil must be kept covered by growing grass and planting

trees on it. (2) Erosion of soil depends upon the slope. Therefore, by

arranging the soil horizontally across the line of the slope, soil

erosion can be reduced. (3) By building bunds to stop the flowing

water which washes away the soil and causes erosion.

* Why is earthworm said to be the farmer’s friend ?

Ans. The earthworm is said to be the farmer’s friend. It is

because of its burrowing habit, the soil becomes loose and

aerated. Thus oxygen of the air can easily reach the roots of the

plants. The loose soil also helps in the easy penetration of roots

deep into the soil. Besides, the earthworms throw their

castings rich in humus which makes the soil more fertile.

* What is meant by terra cotta ? What are its uses ?

Ans. Terra cotta means hard, fired clay, brownish red in

colour. It is used to make earthenware like pots and

sculptures. Once the articles made from terra cotta are

baked, it takes many years for them to change back into the

soil. Terra cotta thus destroys or degrades the soil.

Answers to the Questions

* (1) Which crops are grown in sandy soil ?

Ans. Cucumber, muskmelon, watermelon and fenugreek

are the crops that are grown in sandy soil.

* (2) Why is the soil on the river banks fertile ?

Ans. The soil on the river bank is muddy. It contains

large amounts of organic matter besides other nutrients. Crops

get plenty of nutrients from it. The soil on the river banks,

therefore, is fertile.

Q. 2 Write short notes on the following :

(1) Soil – a natural resource (2) Social forestry (3) Soil

polution (4) Soil testing.

Ans. (1) Soil – a natural resource : (1) The soil is an

important natural resource. (2) Without soil plant life would not

have established on the earth. (3) Plants provide food for animals.

(4) Plants meet our three basic needs, viz., food, clothing and

shelter. (5) Soil provides different kinds of minerals and metals.

(6) Soil holds water which is made available to us. Thus soil is an

important natural resource.

(2) Social forestry : (1) Planting trees on the borders of fields,

on the banks of rivers and streams, on the sides of roads and

railway tracks, etc. is called social forestry. (2) The Government of

India started the social forestry project in the year 1976. (3) This

project encouraged farmers and adivasis to take up plantation of

trees in all possible places. They were provided financial

assistance for this project. (4) Owing to the social forestry project,

the fallow land and barren land has been reclaimed and changed

into the agricultural land. (5) The Maharashtra Government has

carried out the social forestry project in many schools by teams

called ‘Green Brigade’ or the ‘Harit Sena’.

(3) Soil pollution : (1) A disturbance in the natural balance of

the various constituents of the soil is called soil pollution.

(2) Chemical fertilizers, pesticides used by farmers and industrial

effluents pollute the soil. (3) Plants do not grow well on polluted

soil. (4) Soil pollution can be prevented by using organic fertilizers

instead of chemical fertilizers. (5) Besides, overuse of fertilizers

and pesticides should also be avoided for the prevention of soil

pollution. Effluents from factories should be treated properly before

letting out.

(4) Soil testing : (1) Soil testing is done to find out the quality

of the soil. (2) It helps to know about the good qualities of soil and

its shortcomings. (3) Soil testing also helps to find out the colour,

texture and the content of organic matter in the soil.

Q. 3 Distinguish between Sandy soil, Clayey soil and Silt

soil.

Ans. Differences between Sandy soil, Clayey soil and Silt soil :

Sandy soil Clayey soil Silt soil

1. Sandy soil has

greater proportion

of large

particles of soil.

1. Clayey soil has

greatest proportion

of fine

particles of soil.

1. Silt soil consists of

fine to mediumsized

soil

particles.

2. Sandy soil has the

least capacity for

holding water.

2. Clayey soil has the

greatest capacity

for holding water.

2. Silt soil has

medium capacity

for holding

water.

3. Sandy soil is

highly aerated.

3. Clayey soil is less

aerated.

3. Silt soil is well

aerated.

Q. 4 Give scientific reasons :

(1) Soil has an important place in human life.

Ans. (1) Man is dependent on plants for his three basic needs,

i.e. food, clothing and shelter. (2) Plants provide food to man, wood

for building shelters and clothes for protection from cold. (3) Plants

develop because of the presence of soil. (4) Without soil plant life

could not have established on the earth. (5) Thus, soil has an

important place in human life.

(2) The articles made from soil become hard on baking.

Ans. (1) Soil has the property of plasticity, i.e. it can be given

any desired shape. (2) When articles made from soil are baked, the

minerals present in soil melt and when cooled, bind the other

particles of soil together. (3) Thus, the articles made from soil

become hard on baking.

(3) Kaolin is called China clay.

Ans. (1) Kaolin is white coloured soil found near the Kaolin

mountain in China. (2) Since Kaolin is found only in China, it is

called China clay.

(4) The growth of roots in the clayey soil is arrested.

Ans. (1) Clayey soil has the greatest proportion of fine

particles. (2) It has the greatest capacity for holding water. (3) The

soil which holds a lot of water is not well aerated. (4) Owing to this,

the growth of roots in the clayey soil is arrested.

(5) The grass should be allowed to grow on the land.

Ans. (1) The grass that grows on the soil provides cover.

(2) This cover prevents soil erosion. (3) The grass, therefore,

should be allowed to grow on the land.

(6) The Government department for soil conservation is

located at the district place.

Ans. (1) The Department of soil conservation provides

information about the conservation of soil. (2) To enable the

farmers to get the information easily about how soil erosion can be

reduced, the Government department for soil conservation is

located at the district place.

(7) Use of too much water and chemicals should be

avoided.

Ans. (1) Use of too much water and chemicals make the soil

saline. (2) In saline soil, natural balance of the constituents is lost.

Such soil becomes polluted and infertile. (3) Crops cannot be grown

here. (4) The use of too much water and chemicals, therefore,

should be avoided.

(8) Organic fertilizers should be used instead of chemical

fertilizers.

Ans. (1) Chemical fertilizers decrease the fertility of the soil.

(2) Besides, they produce soil pollution. (3) To prevent soil

pollution and to increase the fertility of the soil, organic fertilizers

should be used instead of chemical fertilizers.

Q. 5 Answer the following questions in one sentence

each :

(1) How does rock break in the cold ?

Ans. Water stored in the cracks of rock freezes in the cold, as a

result of which its volume increases resulting in the breaking of the

rock.

(2) How do rodents help in the formation of soil ?

Ans. Rodents like rats and bandicoots make burrows in the

soil to live, which results in the conversion of rough earth into soil.

(3) How much time does it take to form a 2.5 cm thick

fertile layer of soil ?

Ans. It takes about 800 to 1000 years to form a 2.5 cm thick

fertile layer of soil.

(4) What do you mean by the plasticity of soil ?

Ans. The property of giving a desired shape to the soil is called

plasticity of soil.

(5) What idea do we get from the colour of the soil ?

Ans. We get an idea of the fertility, drainage and other such

properties of the soil from its colour.

(6) Which minerals are found in the soil along with the

organic matter ?

Ans. Minerals such as quartz, felspar, mica, carbonates of

metals, oxides and sulphides of iron are found along with the

organic matter in the soil.

(7) How is washed away soil from the fields, be retained in

its place ?

Ans. The washed away soil from the fields can be retained in

its place by building bunds to stop the flowing water.

 (8) What information do you get from the Government

Soil Conservation Department?

Ans. We get information about how soil erosion can be

reduced from the Government Soil Conservation Department.

* (9) Which are the constituents of plant origin in the soil ?

Ans. Bacteria, algae, blue green algae, fungi, decomposed

leaves of plants, etc. are the constituents of plant origin in the soil.

Q. 6 Find the odd man out and give reasons :

(1) Food, Clothing, Shelter, Air.

(2) Nurture of Plants, Weathering, Holding water, Storage of

minerals.

(3) Quick lime, Bricks, Vessels, Wall.

(4) Quartz, Felspar, Mica, Kaolin.

(5) Protozoa, Fungi, Algae, Bacteria.

(6) Protozoa, Worms, Fungi, Insects.

(7) Growing grass, Growing crops, Afforestation, House

construction.

(8) Acid rain, Sewage water, Weathering, Overuse of water.

Ans. (1) Air. Others are basic necessities of human beings.

(2) Weathering. Others are properties of soil. (3) Quick lime.

Others are made from the soil. (4) Kaolin. Others are soil minerals.

(5) Protozoa. Others are constituents of plant origin. (6) Fungi.

Others are the constituents of animal origin. (7) House

construction. Others provide soil cover. (8) Weathering. Others

cause soil pollution.

Q. 7 Considering the correlation between the words of

the first pair, match the third word with the most appropriate

answer :

(1) Conversion of rock into the soil : Weathering : : Soil

testing : ………

(2) Blue green algae : Constituent of Plant origin : :

Worms : ……….

(3) Soil care : Soil conversion : : Protection of forests : ……….

(4) Social forestry : Government of India : : Green

Brigade : ……….

Ans. (1) To test the constituents of soil (2) Constituent of

animal origin (3) Afforestation (4) Government of Maharashtra.

Q. 8 State whether the following statements are True or

False. If a statement is false, correct it and rewrite :

(1) Freezing water decreases in volume and results in the

breaking of rocks.

(2) Changes in the atmospheric heat and cold have an effect on

rocks.

(3) Soil gets polluted if natural organic fertilizers are used.

(4) Biological processes go on in the ground continuously.

(5) Earthworms are called foes of the farmers.

(6) Minerals and metals are not obtained from the soil.

(7) Soil is an artificial natural resource.

(8) Sandy soil is a kind of Kaolin.

(9) Soil which holds a lot of water is not well aerated.

(10) The soil near the banks of a river is fertile.

(11) As people set up habitations near forests, forests began to

be destroyed.

(12) Under social forestry projects, small farmers and adivasis

are encouraged to plant trees.

(13) Soil becomes fertile due to acid rains.

(14) Water, let out from factories does not pollute the soil.

(15) Soil testing helps us to know about the good qualities of soil

and its short comings.

* (16) The texture of soil can be determined from its colour.

* (17) Soil is formed by the fast flowing currents of water.

* (18) Sandy soil has little capacity for holding water.

Ans. (1) False. Freezing water increases in volume and result

in the breaking of rocks. (2) True. (3) False. Soil gets polluted if

artificial chemical fertilizers are used. (4) True. (5) False.

Earthworms are called friends of the farmers. (6) False. Minerals

and metals are obtained from the soil. (7) False. Soil is a natural

resource. (8) False. Clay and loamy soil are kinds of Kaolin

(9) True. (10) True. (11) True. (12) True. (13) False. Soil gets

polluted due to acid rains. (14) False. Water, let out from factories

pollutes the soil. (15) True. (16) False. The texture of soil can be

determined from the proportion of the particles of different sizes.

(17) False. Soil is eroded by the fast flowing currents of water.

(18) True.

Q. 9 Fill in the blanks :

1. (1) Changes in atmosphere cause rocky surfaces to develop

……….

(2) The transformation of rocks into soil is called ……… .

(3) ……… like rats and bandicoots make burrows in the soil to

live in them.

* (4) Plants satisfy man’s basic needs for ………, ……… and

……… .

(5) The property of soil which gives any desired shape to it is

called ……… .

Ans. (1) cracks (2) weathering (3) Rodents (4) food, clothing

and shelter (5) plasticity.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

2. (1) Various kinds of………are used to decorate earthenware or

porcelain articles.

(2) Clay and loamy soil are different types of ……… .

* (3) The organic constituents of soil are of ………and ……… .

* (4) Land should be ……… to prevent erosion.

(5) Arresting soil erosion is called ……… .

Ans. (1) oxides (2) kaolin (3) plant origin, animal origin

(4) covered (5) soil conservation.

-- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- -- --

3. * (1) The Government has started the ……… project to protect

forests.

* (2) Disturbance of the natural balance of soil is called soil

……… .

(3) Using too much water and chemicals makes the soil……….

(4) Soil testing helps to find out the ……… of soil.

(5) The ……… of the soil depends upon the types of the soil.

Ans. (1) social forestry (2) pollution (3) saline (4) quality

(5) utility.

Q. 10 Choose the correct alternatives and complete the

following statements :

(1) The survival of animals, their nourishment and nurture all

depend on the ……… .

(a) air (b) water (c) sea (d) soil

 (2) Rodents make burrows in the soil which results in the

conversion of ……… into the soil.

(a) sand (b) rough earth

(c) rocks (d) cement

(3) The soil formed by weathering caused by roots is generally

……… .

(a) clay (b) loam (c) China clay (d) Kaolin

(4) The formation of a 2.5 cm thick layer of fertile soil takes

about ……… to ……… years.

(a) 50,100 (b) 800,1000

(c) 2000, 3000 (d) 5000, 8000

(5) Plants provide food, clothing and shelter – the three ………

necessities of human beings.

(a) physical (b) basic

(c) economical (d) social

(6) Soil is a ……… resource.

(a) natural (b) artificial

(c) foreign (d) biological

(7) When articles made from clay are baked, they become

……… .

(a) soft (b) hard (c) small (d) big

(8) Bricks that are used for construction work are made from

……… .

(a) iron (b) rocks (c) clay soil (d) sand

(9) Laboratory apparatuses and tiles for bathrooms are made

from ……….

(a) Kaolin (b) concrete (c) cement (d) felspar

(10) Clayey soil has the………proportion of fine particles of soil.

(a) medium (b) greatest (c) lesser (d) greater

(11) The Government department for soil conservation is

located at the ……….

(a) district place (b) village (c) city (d) taluka

(12) The Government of India first started social forestry project

in the year ……… .

(a) 1976 (b) 1979 (c) 1986 (d) 1988

 (13) The social forestry project of the Maharashtra Government

is carried out in most schools by teams called the ……… .

(a) Harit sena (b) Vana sena

(c) Vanar sena (d) Dhaval sena

(14) A disturbance in the natural balance of the various factors

present in soil is called ……… .

(a) weathering (b) soil pollution

(c) soil testing (d) soil degradation

Ans. (1) soil (2) rough earth (3) clay (4) 800,1000 (5) basic

(6) natural (7) hard (8) clay soil (9) Kaolin (10) greatest

(11) district place (12) 1976 (13) Harit sena (14) soil pollution.

Q. 11 Match the following :

* [1] ‘A’ ‘B’

(1) Algae

(2) Soil erosion

(3) Social forestry

(a) Planting trees on the

borders of the fields

(b) Factors of plant origin

(c) (Gusts of) wind

(d) Factors of animal origin

Ans. (1) Algae – Factors of plant origin (2) Soil erosion – (Gusts

of) wind (3) Social forestry – Planting trees on the borders of the

fields.

[2] ‘A’ ‘B’

(1) Kaolin

(2) Iron oxide

(3) Copper oxide

(a) Red ochre

(b) Green

(c) White

(d) Orange

Ans. (1) Kaolin – White (2) Iron oxide – Red ochre (3) Copper

oxide – Green.

[3] ‘A’ ‘B’

(Type of soil) (Water holding capacity)

(1) Sandy soil

(2) Clayey soil

(3) Silt soil

(a) Greatest

(b) Medium

(c) Least

Ans. (1) Sandy soil – Least (2) Clayey soil – Greatest (3) Silt

soil – Medium.

16. SOIL 213

[4] ‘A’ ‘B’

(1) Protozoa

(2) Soil particle

(3) Soil colour

(4) Soil pollution

(a) Soil texture

(b) Soil constituent of animal origin

(c) Sewage water

(d) Chemical constituent

(e) River water

Ans. (1) Protozoa – Soil constituent of animal origin (2) Soil

particle – Soil texture (3) Soil colour – Chemical constituent (4) Soil

pollution – Sewage water.