Soil is the upper most layer of earth crust.

Composition of Soil

Mineral Particles : Soil contains mainly three types of particles : Gravel, sand and clay. These particles determine the texture as well as type of the soil.

Inorganic Substances : Soil contains nitrates, sulphates, phosphates and carbonates of potassium, magnesium, sodium and iron. These salts are derived from the parent rock from which the soil is formed.

Organic substances (Humus) : Organic substances are added to the soil by the activities of plants and animals. Their death and decomposition add organic material to the soil. The completely decomposed product of plants and animals is called humus. It makes the soil fertile and improves its water holding capacity. It also encourages the growth of useful microbes in the soil.

Water : All types of soils generally contain water in the spaces present between the soil particles. Water is needed for plant growth. The type of soil determines its water holding capacity or the amount of water contained in that type of soil.

Air : Air is also present in the soil in the spaces between the soil particles. It is needed for respiration of plants as well as for other living organisms in the soil.

Soil Profile

A side view of the vertical section cut through the soil to the underlying solid through the soil to the underlying solid rocks shows a soil profile (fig.). Most of the soil profiles consist of three layers which are called horizons. These horizons are lettered as A, B and C, the details of which are given below :

soil profile


It is the uppermost layer and is usually the darkest in colour. It contains a lot of humus. Humus makes the soil fertile. Many living microorganisms are also seen in this layer. The soil here is porous, soft and has more water holding capacity than the other layers. The roots of many plants absorb their food from this layer. This layer of soil is also known as the topsoil.


It lies under the layer of topsoil and is comparatively harder and more compact. This is also called the subsoil. It is lighter in colour and is often grey or red. It contains more sand and also some stones. Only a few plants or trees have roots long enough to reach the subsoil. Subsoil is not suitable for plant growth as it contains very little organic matter.

C-Horizon :

It is the lowermost part of the soil and lies beneath the subsoil. It is made of stones and rocks. It contains no organic matter. However, minerals are found in this layer. Beneath this layer lies solid rock called bedrock.

Soil as a Natural Resource

Soil is the most important natural resource available to man. It is considered a valuable resource because of the following reasons :

A Base for Growing Crops

It is the base on which all plants grow. All plants get anchorage, minerals, water and air from the soil.

Storehouse of Minerals

A large number of minerals are present in the soil. These minerals are extracted and made use of in a large number of industries. Some of the common minerals found in the soil are saltpetre, rocksalt, gypsum, bauxite, haematite and calcite.

Allows Activities that are a source of employment

Soil is used for various purposes. It is used for the construction of buildings, roads, bridges, industries, dams, etc. It is also used for cultivation of crops. All these activities give employment to thousands of people.

Soil as a Raw Material

Soil is used as a raw material for making bricks, mortar, pottery and other materials. It is also used in building huts and sheds.

Habitat for Microorganisms :

Soil makes a very good natural habitat for various microorganisms. These microorganisms form humus and make the soil fertile.

Among the animals living in the soil are insects, while ants, grasshoppers, centipedes, millipedes, scorpions, beetles, earthworms and sandworms. Big animals like moles, rats and rabbits build their homes in the soil. Earthworm is popularly known as the farmer’s friend or as nature’s ploughman because of its activities in the soil. It makes burrows into the soil, thus mixing the soil, well, and its excreta called wormcast enriches the soil with nitrogen.

Water storage :

Rainwater percolates through the soil and accumulates above bedrock to form the water table. This water is pumped out by us for domestic or agricultural uses.

Soil Erosion

Process of carrying away of topsoil by natural forces like water and wind is called soil erosion.

Causes of soil Erosion

  • Large scale cutting of trees (deforestation)
  • Overgrazing by animals in forest.
  • Improper farming practices.
  • Heavy rains or floods.
  • Forest fires.

Prevention of soil Erosion :

  • Grow more trees on a large scale (afforestation)
  • Flood control.
  • Allow restricted animal grazing.
  • Follow terrace farming.
  • Construct bunds.

Read this also : Nutrition in Plants

Soil Pollution

The contamination of soil with excess use of fertilizers, insecticides, herbicides, weedicides etc., and dumping of industrial waste, sewage and garbage is called soil pollution. Any substance which lowers the fertility of the soil is a soil pollutant.

Causes of soil pollution

  • Excessive use of chemical fertilizers and pesticides.
  • Dumping of garbage and sewage waste in the soil.
  • Chemical wastes from industries, mines, and factories, etc.
  • Waste materials likes plastics and metals.

Preventing soil Pollution

  • Dispose off sewage properly.
  • Recycle waste.
  • Use organic manure or vermicomposting.
  • Treat industrial effluents before discharge.

Types of soil

Sandy soil

This contains more than 60 per cent sand along with some clay. The water holding capacity of sandy soil is very poor. There is a lot of air present in this type of soil. This type of soil is not suited for the growth of plants as it does not retain water of humus in it and is poor in nutrients. Usually, gram, barley, jowar and maize are grown in sandy soils as rained crops.

Clayey Soil

It consists mostly of clay particles, the sand particles being far less in proportion. Clayey soil is very sticky and so tilling is difficult. It is usually used for making pots and toys.

made of clay

This soil has very good water holding capacity. It is badly aerated and is easily water logged. However, clayey soil is rich in minerals which make it good for the growth of plants. This type of soil is good of crops like paddy which required a lot of water.

Loamy Soil

It consists of a good mixture of sand, clay and humus. It has good water holding capacity. It has sufficient aeration. Plants get sufficient mineral salts from this soil. Therefore, loamy soil is the best soil for growing plants. Crops like wheat, barley, mustard, pulses, cotton, fruits and vegetables can be profitably grown in loamy soils.



As animals do not have chlorophyll, they can’t prepare their food own. They obtain their food directly or indirectly from plants. Animals may be herbivores, carnivores or omnivores.

Holozoic nutrition

In this type of nutrition, animals take in solid food such as fruits, vegetable & meat, etc.

Five steps in the process of holozoic nutrition in animals. are –

(1)  Ingestion

(2)  Digestion

(3)  Absorption

(4) Assimilation

(5)  Egestion

Nutrition in Amoeba : Amoeba is a unicellular animal. It eats microscopic plants & animals that float in water.

The complete process of nutrition in amoeba is as follows –

Ingestion : An amoeba ingests food by using its pseudopodia. When a food particles comes near an amoeba, it ingests this food particle by surrounding it with its pseudopodia. The pseudopodia close to form a small cavity called food vacuole.

 Digestion : The food is digested in the food vacuole by digestive enzymes.

Absorption : The digested food present in the food vacuole is absorbed directly into the cytoplasm of amoeba by diffusion. The digested food just spreads out from the food vacuole into the cytoplasm of amoeba cell.

Assimilation : Food absorbed by amoeba is used to obtain energy for maintaining life process.

Egestion : When a sufficient amount of undigested food collects inside amoeba, then its cell membrane suddenly ruptures at any place & the undigested food is thrown of the cell.

Process of nutrition in amoeba

Nutrition in Human

  • Nutrition in human is holozoic. The food ingested through the mouth passes through a number of organ in our body which constitute the alimentary canal.
  • The alimentary canal along with digestive glands known as digesttive system.
  • The digestive system of human consists of following organs –

Digestive System of Human

Mouth : It is a transvers slit & also called opening of alimentary canal. Mouth opens into buccle cavity.

Buccle cavity : Mouth open into a cavity which contain teeth, tongue & salivary glands. Salivary glands secrete saliva which contain salivary amylase enzyme & convert the starch into simple sugar.

Teeth : Teeth are hard structures held in sockets of the jaws. Teeth cut, chew and break food into smaller pieces.

Tongue : Tongue is the organ used for taste. It contains taste buds to distinguish whether a type of food is sweet, sour, bitter or hot (figure). It also helps in rolling and pushing the food into the pharynx. It mixes the saliva with the food and also helps us in speaking.

Tongue and its test

Oesophagus or Food Pipes : It is a connecting tube between the mouth and stomach. The food is pushed down towards the stomach by the movement of the muscles of the food pipe.

movement of the food

Stomach : Stomach is a J-shaped bag-like structure made of muscles. The stomach secretes gastric juice and hydrochloric acid. Hydrochloric acid kills microorganisms and provides an acidic medium for effective digestion. In the stomach food is throughly mixed with the gastric juice secreted by the gastric glands present in the stomach. The gastric juice contians an enzyme called pepsin which helps to break down proteins into simpler substances.

Small Intestine : It is a coiled tube and is about 7 metres in length. It consists of three parts, namely dueodenum, jejunum and ileum. In the small intestine the food is mixed with bile juice and pancreatic juice. These are secreted by the liver and the pancreas, respectively. Bile juice breaks down fats into fatty acids and glycerol. The pancreatic juice breaks down starch into simple sugar and proteins into amino acids. Digestion of all the components of food gets completed here and the end products are ready for absorption.

Absorption of food occurs through millions of small projections in the inner walls of the part of small intestine called ileum. These projections are known as villi. The incorporation of absorbed nutrients into the cell components is called assimilation.

The food that remains undigested and unabsorbed then enters the large intestine.

Large intestine : It is the last organ of the digestive system. It is about 1.5 m in length. It consists of three parts, namely caecum, colon and rectum. It helps in absorbing water and in removing undigested solid wastes from the body in the form of faeces through an opening called anus.

Anus : It is the last part of the alimentary canal. Its main function is to expel solid faceces out of the body.

Digestive Glands :

  • Salivary Glands : There are three pairs of salivary glands located in the mouth. Salivary glands secrete saliva which contains amylase enzyme. Amylase works on starch and converts it into simple sugar.
  • Liver : It is reddish brown gland and is located in the upper part of the abdomen. It secretes bile juice that is stored in gallbladder. The bile helps in breaking down fat into simpler substances.
  • Pancreas : It is a cream-coloured gland and is located just below the stomach. It secretes pancreatic juice into a small intestine. It acts on carbohydrates and protein and converts them into simpler substances.

Nutrition in a ruminant

A ruminant is an herbivours animal which regurgitates its food & digest it in step. For example- Cow, goats, sheep etc.

The 2 steps involved in digestion of ruminants are –

  1. The ruminant first eats the foods & regurgitates a semi digested food called cud.
  2. The ruminant then eats the cud when at rest. This process of eating the cud is called ruminating.

Ruminants have a special stomach with 4 chambers, which are as follows –

  • Rumen : This is the largest chamber of the stomach. It is namely used for storing food.
  • Reticulum : It helps in moving the food bakc to the mouth when needed.
  • Omasum : This is the smallest chamber of the stomach. Its main function is to absorb excess water.
  • Abomasum : This is a true stomach where gastric juices are secreted to help digestion. Here the food is digested just like in the human stomach.

Digestion of food in ruminants

The ruminants mostly eat grasses and leaves which are rich in cellulose, The ruminants can digest cellulose becuase celluose-digesting bacteria and protozoa are present in their stomach.

4 chambered stomach

 Half-chewed grass travels from the mouth to the first chamber of the stomach called rumen where it is acted upon by bacteria and microorganism. It then goes into the reticulum from where it is returned to the mouth as cud for through chewing called rumination. It enters a third chamber called omasum. Here it is broken down into still smaller pieces. Finally, it enters the fourth chmaber called abomasum where enzymes act upon it and digestion is completed. It is finally sent to the small intestine where the absorption of the nutrients takes place.

Read this Also : Nutrition in Plants Class 7

Exercise Based on Nutrition in Animals

Exercise : 1 

Single Choice Question

1. Digestion within a digestive tract is –

(A) incomplete

(B) extracellular

(C) the same as absorption

(D) an irreversible process

2. Which of the following regioins of the alimentary canal of man does not secrete a digestive enzyme ?

(A) Oesophagus

(B) Stomach

(C) Duodenum

(D) Mouth

3. A digestive enzyme, salivary amylase, in the saliva begin digestion of –

(A) protein                  (B) nucleic acids

(C) facts                      (D) carbohydrates

4. If you chew on a piece of bread long enough, it will begin to taste sweet because –

(A) maltase is breaking down maltose

(B) lipases are forming fatty acids

(C) amylase is breaking down starches to disaccharides

(D) disaccharides are forming glucose

5. Saliva has the enzyme –

(A) pepsin                   (B) ptyalin

(C) trypsin                  (D) rennin

6. Pepsin digests –

(A) proteins in stomach

(B) carbohydrates in duodenum

(C) proteins in duodenum

(D) fats in ileum

7. Chief function of HCl is –

(A) to maintain a low pH to prevent growth of micro-organisms

(B) to facilitate absorption

(C) to maintain low pH to activate pepsinogen to form pepsin

(D) to dissolve enzyme secreted in stomach

8. If the stomach did not produce any hydrochloric acid, which enzyme will not function ?

(A) Ptyalin                  (B) Trypsin

(C) Pepsin                   (D) Collagenase

9. Chief function of bile is –

(A) to digest fat by enzymatic action

(B) to emulsify fat for digestion

(C) to eliminate waste product

(D) to regulate process of digestion

10. Where is bile produced ?

(A) In gall bladder       (B) In blood

(C) In liver                  (D) In spleen

11. Ileum is –

(A) First part of the small intestine

(B) Middle part of the small intestine

(C) Last part of the small intestine

(D) Not a part of the small intestine

12. Largest gland in human body is –

(A) liver                      (B) pancreas

(C) pituitary                (D) thyroid

13. Which of the following organs produces bile ?

(A) liver                     (B) pancreas

(C) gallbladder            (D) gastric gland

14. Which of the following is not a part of nutrition-

(A) digestion               (B) absorption

(C) excretion               (D) assimilation

15. Which of the organs produces bile ?

(A) liver                     (B) pancreas

(C) gallbladder            (D) gastric gland

16. An amoeba ingests food by –

(A) cilia                      (B) tentacles

(C) pseudopodia          (D) feeding tube

17. The walls of the large intestine absorb –

(A) cellulose               (B) water

(C) digested food         (D) digested proteins

18. Small intestine have this to increase the surface area for absorption –

(A) villi                      (B) glands

(C) liver                      (D) pancreas

19. Juice secreated by liver is –

(A) bile                       (B) gastric

(C) pancreatic             (D) acid

20. Number of chambers in the stomach of ruminats is –

(A) 4         (B) 3         (C) 2        (D) 1

 21. The part of digestive system which helps in mixing food with saliva is –

(A) teeth                     (B) oesophagus

(C) tongue                   (D) lips


Fill in the Blank

22. Salivary amylase works on ………………… .

23. Incisor teeth help in …………………. the food.

24. The liver and ………………….. are used for procuring food.

25. In amoeba ……………… are used for procuring food.

26. There are …………………. number of teeth in a temporary set of teeth.

Exercise : 2 

Very Short Answer Type

  1. Name the organs that make the alimentary canal.
  2. Mention the various steps involved in the process of nutrition.
  3. Which type of carbohydrate cannot be digested by humans ?
  4. What is the role of hydrochloric acid in the stomach ?
  5. Why do we call animals heterotrophs ?
  6. Name the type of nutrition in amoeba.
  7. Which organs help to sense the different taste ?
  8. Differentiate between ingestion and egestion.
  9. What is the function of villi ?

Short Answer Type

  1. What happens to digested food after absorption
  2. How does an amoeba capture its food ?
  3. What are villi ? What is their location and function ?
  4. Which is the largest chamber of the ruminant stomach ? What is its role ?
  5. What is the juice secreted by the liver called ? What does it do ?
  6. What happens to food in the small intestine ?
  7. What is pancreas and where is it located ?
  8. Define intracellular digestion. Give two examples of animals where this type of digestion take places.

Long Answer Type

  1. Draw a diagram of the tongue to show the location of various taste buds.
  2. Give an account of the various modes in which animals obtain food.
  3. Explain the process of digestion in ruminants.
  4. Which digestive juice is secreted in the mouth ? What enzyme does it contain and what is its function ?
  5. Draw a labelled digram of the alimentary cannal of humans.
  6. What are digestive glands ? Name three such glands that are present in the human body. What are their secretions called ?
  7. What is the role of stomach in the digestion process ?
  8. What happens to the food in the small intestine ?