Chapter 2 Science CBSE 7th


Class 7

Chapter 2

Nutrition in Animals

Important topics covered in NCERT for Class 7 Science Chapter 1 – Nutrition in Animals

  • Ways of food intake
  • Humans digestion
  • Digestion in herbivores
  • Nutrition and digestion in Amoeba
Concept Map
Concept Map

Important Terms

  • Buccal cavity : The cavity of mouth, with all its internal parts like cheeks, teeth, tongue and salivary glands is called buccal cavity.
  • Cellulose : A type of carbohydrate. Many animals including human cannot digest cellulose.
  • Glycerol : It is one of the constituents of fat. It combines with fatty acid to from fats.
  • Fatty Acids : One of the main constituents of fats.
  • Ingestion : Process of taking food into the body.
  • Digestion : The breakdown of complex components of food (which cannot be utilised by our body) into simpler and absorbable substances is called digestion.
  • Absorption : The passage of digested food into the blood vessels is called absorption of food. This process takes place in the small intestine in case of human beings.
  • Assimilation : The process in which the absorbed food is used for producing energy and growth is called assimilation.
  • Egestion : The removal of undigested and unabsorbed food material, called faecal matter through the anus from time to time is called egestion.
  • Tooth decay : After eating food, especially sweets, chocolates, cold drink and other sugars, if mouth is not washed properly, then some leftover food and sugars remain attached to teeth. The harmful bacteria break down the sugars and release acids. The acids gradually damage the teeth. This is called tooth decay which may lead to toothache and even loss of tooth.

Arrangement of different types of Teeth:


Types of Teeth with Functions

Types of TeethNumber in each half of the jawStructureFunction
Incisors (Front teeth)1Have flat, sharp edgesCutting and biting the food
Canines2Sharp and conicalTearing and piercing
Premolars2Bicuspids and have one or two rootsCrushing and grinding
Molars3Four or five cusps, have more than one rootCrushing, grinding and mastication

Number and types of teeth in man

Types of TeethMilk teethPermanent teeth
Incisors (Front teeth)44
Total number of teeth2032

Amazing fact: Starfish feeds on animals covered by hard shells of calcium carbonate.ScC1img12ORS (Oral Rehydration Solution) : It is prepared by dissolving a pinch of salt and sugar in boiled and cooled water. It prevents dehydration of the body due to diarrhoea and vomiting.

Revision Notes

Nutrition: The process by which an organism takes food and utilizes it is called nutrition.
Need of Nutrition: Organisms need energy to perform various activities. The energy is supplied by the nutrients. Organisms need various raw materials for growth and repair. These raw materials are provided by nutrients.
Animal Nutrition: Plants make their food by the process of photosynthesis, but animals cannot make their food themselves. Animals get their food from plants. Some animals eat plants directly while some animals eat plant eating animals. Thus, animals get their food from plants either directly or indirectly. All organisms require food for survival and growth. Requirement of nutrients, mode of intake of food and its utilization in body are collectively known as nutrition.

Nutrition in complex animals involves following steps:

  1. Ingestion: The process of taking food into the body is called ingestion. Method of ingestion, i.e. taking of food, varies from one animal to another.
  2. Digestion: The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, etc.
  3. Absorption: The process of passing of digested food into blood vessels in the intestine is called the absorption.
  4. Assimilation: The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation. In other words, assimilation is the conversion of absorbed food (nutrients) into living tissues. Through the process of assimilation our cells are supplied with oxygen and nutrients.
  5. Egestion: Removal of waste materials from the body is called egestion. The faecal matter is removed through the anus from time-to-time. Since the waste of food left after digestion is also called faeces, hence the process of egestion is also known as defecation.

Different Ways of Taking Food: The mode of taking food into the body varies in different organisms. Different organism takes food in different ways.

  • Bees and humming-birds suck the nectar of plants
  • Infants of human and many other animals feed upon their mother’s milk by sucking them.
  • Snakes like the python swallow the animals they prey upon.
  • Human beings use their hands to put food into their mouth and swallow the food after chewing.
  • A snake swallows the animals they prey upon without chewing them.
  • A frog captures prey with its sticky tongue.
  • An earthworm uses its muscular pharynx to swallow its food.
  • Spiders weave sticky web in which small insects get stuck.
  • Some aquatic animals filter tiny particles floating nearby and feed upon them.
  • Amoeba, a unicellular animal, engulfs tiny particles of food by using pseudopodia. Amoeba surrounds the food by pseudopodia and then makes a food vacuole to engulf the food.
  • In multicellular organisms; like hydra there are numerous tentacles around their mouth. Hydra uses tentacles to surround its prey and kill them with its stinging cells. Then the food is pushed inside the body cavity.

Digestion: The process of breaking down of complex component of food into simpler substances is called digestion. The process of digestion is different in human, grass eating animals, amoeba, hydra, etc.

  • Enzymes help in the breakdown of complex molecules like carbohydrates, protein, fats, etc. into simple molecules.
  • Digestion in unicellular animals; like Amoeba; is intracellular. The digestive enzymes are secreted in the food vacuoles.

Digestion in Human: We take in food through the mouth, digest and utilise it. The digestive system of humans is well developed. Human digestive system consists of alimentary canal and its associated human digestive system glands.

Various organs of human digestive system in sequence are

  • Mouth (Buccal Cavity)
  • Oesophagus (food Pipe)
  • Stomach
  • Small intestine
  • Large intestine
  • Rectum
  • Anus.

The glands which are associated with human digestive system are:

  • Salivary glands- Located in mouth or Buccal Cavity
  • Liver- It is the largest gland situated in the upper part of abdomen on the right side.
  • Pancreas- located just below the stomach

The ducts of various glands open into the alimentary canal and pour secretion of their juices into the alimentary canal.

  • Mouth: The food is ingested through the mouth. The mouth contains tongue, teeth and salivary glands. Teeth break the food into smaller particles. This process is called mastication. The chewed food is mixed with saliva. Saliva is a watery fluid secreted by the salivary glands.
  • Saliva contains a type of enzyme called the salivary amylase, which converts starch into sugar.
  • Teeth: Our teeth cut, tear and grind the food before we swallow it. There are four types of teeth in our mouth.
    1. Incisors: These are flat and chisel-shaped teeth. They lie in the front of the mouth. There are eight incisor teeth; four in the upper jaw and four in the lower jaw. The incisor teeth are well adapted for cutting and biting of food items.
    2. Canines: These are round shaped, sharp and pointed teeth. Canines are well adapted to hold and tear the food. There are four canine teeth found in human.
    3. Premolars: There are two premolars on each side of each jaw. Premolars help in crushing and grinding the food. There are 8 premolar teeth in an adult human.
    4. Molars: There are two molars on both sides in both the jaws. They have almost a flat surface with small projections. These teeth are meant for fine grinding of food.


  • There are 12 molar teeth including the wisdom teeth in an adult human. The 4 molar teeth are also called wisdom teeth. Wisdom teeth usually grow between the ages of 18 to 21.
  • The tooth is covered with a white substance called enamel. It is the hardest substance in the human body.

Milk teeth and Permanent teeth

  • In human beings, the teeth grow twice. First time the teeth grow when one is a small baby (or infant). This set of teeth is called milk teeth. Thus, the first set of teeth which grow during infancy (babyhood) are called milk teeth. Milk teeth are a temporary set of teeth. The milk teeth loosen and begin to fall off at the age between 6 and 8 years. When milk teeth fall off in a child, then another set of teeth grow in their place. So, second time the teeth grow when one is a child.
  • The second set of teeth is called permanent teeth. The permanent teeth grow in place of milk teeth. The permanent set of teeth remains till the old age. But when old people lose their permanent teeth, then new teeth do not grow in their place.

Tooth Decay: The white, hard outer covering of tooth is called enamel (see the below Figure). The part of tooth below the enamel is called dentine. Dentine is similar to bone. Inside the dentine is pulp cavity which contains nerves and blood vessels. lf the teeth are not cleaned regularly, then tooth decay can take place. Tooth decay is a process in which the tooth becomes rotten due to the formation of cavities (holes) inside it leading to toothache.


  • If we do not clean our teeth and mouth after eating food, then many harmful bacteria begin to row and live on the teeth. These bacteria act on the sugar present in the left-over food particles sticking to the teeth to form acid. The acid thus formed eats up the enamel and dentine of the tooth gradually and ultimately makes a cavity (or hole) in the tooth [see the below Figure(a)].


  • When this cavity (or hole) reaches the pulp cavity of the tooth (which contains nerves), our tooth becomes painful and we get toothache [see the below Figure(b)].


Digestive System

  • Tongue: The tongue is a muscular organ. Tongue helps to mix saliva in the food. It also helps to push the food down the food-pipe or oesophagus. Taste receptors are present on tongue and give us the sense of taste.


  • Foodpipe/Oesophagus: It is a tube-like structure connecting the mouth and the stomach. It is about 30 cm. long. Oesophagus has powerful muscles which gently push the food down to the stomach. The oseophagus contracts and relaxes in a rhythmic fashion to facilitate the forward movement of food. This movement happens in other parts of the alimentary canal as well and is called peristalsis. No digestion takes place in oesophagus.


  • Stomach: Stomach is the thick walled bag present on the left side of the abdomen. (see human digestive system figure) It is the widest part of the alimentary canal. Oesophagus brings slightly digested food from mouth into the stomach.
  • The stomach walls contains three tubular glands in it walls which secrete gastric juice. The gastric juice contains three substances: Hydrochloric acid, the enzyme pepsin and mucus. The hydrochloric creates an acidic medium which facilitates the action of the enzyme pepsin that is the digestion of protein into simple substances. The acid kills many bacteria that enter along with the food. The mucus helps to protect the stomach wall from its own secretions of hydrochloric acid. The partially digested food then goes from the stomach into the small intestine.
  • Small intestine: The food leaves the stomach at certain intervals of time and enters into the small intestine.
    • The small intestine is the longest part of the digestive system. It is about 20 feet or seven meters long in an adult human. Small intestine is a highly coiled tube. It consists of three parts: duodenum, jejunum and Ileum.
    • In the duodenum, the liver and pancreas pour their secretions. Liver secretes bile juice and pancreas secretes the pancreatic juice. The bile juice contains the bile which carries out emulsification of fat. In this process, the fat is broken into tiny droplets. The pancreatic juice contains several enzymes. The enzymes of the pancreatic juice break down starch into simple sugars and proteins into amino acids.
    • Minerals and vitamins do not need to be changed because cells are able to absorb them easily. From duodenum the food goes to the lower part of the intestine. There are numerous finger-like projections on the wall of the small intestine. These projections are called villi. They have fine blood capillaries to absorb the food. After absorption; food mixes in the blood stream and is carried to all the cells of the body. The cells utilize this food to release energy.



  • Large intestine: The digested food enters into large intestine after small intestine. The large intestine is wider and shorter than small intestine. It is about 1.5 metre in length. In large intestine; excess of water from the materials is absorbed. The semi solid residue is stored in the last part of the large intestine called rectum and finally throw out of the body through the anus from time to time. The throwing out of waste of digested food from rectum is called egestion. Egestion is also known as defecation.

Digestion in Grass Eating Animals:
Ruminants: None of the animal can digest cellulose which is a major component of the food eaten by herbivores. The plant eating animals digest their food in two steps. Their stomach is divided into four chamber, viz. rumen, reticulum, omasum and abomasum.

First of all, half chewed food is swallowed and it then goes from mouth to the rumen, the first chamber of the stomach. Here, it is acted upon by bacteria. These microorganisms digest the cellulose. This half digested food goes to the second muscular chamber; the reticulum. From the reticulum the food is sent back to the mouth; as cud; to be chewed again. Chewing of the cud is called rumination and such animals are called ruminating animals or ruminants. Cow, goat, buffaloes, sheep, bison, etc. are good example of ruminating animals. The re-chewed food is swallowed for the second time. After passing the first two chambers it enters the third chamber; the omasum. Here the food is further broken down into smaller pieces and finally enters the fourth chamber, the abomasum. Here, all enzymes act upon the food and the digestion is completed.

After digestion and absorption, nutrients from food are taken to the cells in all parts of the body. The cells oxidize the food to release energy.


Feeding and Digestion in Amoeba: Amoeba is a microscopic organism which consists of only a single cell. Amoeba is mostly found in pond water. The figure given below shows the structure of amoeba.ScC2img08Amoeba eats tiny plants and animals as food which floats in water in which it lives. The mode of nutrition in Amoeba is holozoic. The process of obtaining food by Amoeba is called phagocytosis.

Steps involved in the nutrition of Amoeba:

  • Ingestion: Amoeba ingests food by forming temporary finger-like projections called pseudopodia around it. The food is engulfed with a little surrounding water to form a food vacuole (‘temporary stomach’) inside the Amoeba.
  • Digestion: In Amoeba, food is digested in the food vacuole by digestive enzymes which break down the food into small and soluble molecules by chemical reactions.
  • Absorption: The digested simple and soluble substances pass out of food vacuole into the surrounding environment.
  • Assimilation: The absorbed food materials are used to obtain energy through respiration and make the parts of Amoeba cell which leads to the growth of Amoeba.
  • Egestion: The remaining undigested material is moved to the surface of the cell and thrown out of the body of Amoeba.

NCERT Solution

Question 1: Fill in the blanks:
(a) The main steps of nutrition in humans are ___________, ___________, ___________ ,___________ and ___________

The main steps of nutrition in humans are ingestion, digestion, absorption, assimilation and egestion.

(b) The largest gland in the human body is ___________.

The largest gland in the human body is liver.

(c) The stomach releases hydrochloric acid and ___________ juices which act on food.

The stomach releases hydrochloric acid and digestive juices which act on food.

(d) The inner wall of the small intestine has many finger-like outgrowths called ___________

The inner wall of the small intestine has many finger-like outgrowths called villi.

(e) The Amoeba digests its food in the ___________ .

Amoeba digests its food in the food vacuole.

Question 2: Mark ‘T’ if the statement is true and ‘F’ if it is false:
(a) Digestion of starch starts in the stomach.


(b) The tongue helps in mixing food with saliva.


(c) The gall bladder temporarily stores bile.


(d) The ruminants bring back swallowed grass into their mouth and chew it for some time.


Question 3: Tick (√) mark the correct answer in each of the following:
(a) Fat is completely digested in the

(i) stomach
(ii) mouth
(iii) small intestine
(iv) large intestine

(iii) Small intestine

(b) Water from the undigested food is absorbed mainly in the:

(i) Stomach
(ii) Food pipe
(iii) Small intestine
(iv) Large intestine

(iv) Large intestine

Question 4: Match the items of column I with those given in column II:

Column 1Column 2
Food ComponentsProduct(s) of digestion
CarbohydratesFatty acids and glycerol
FatsAmino acids
Column 1Column 2
Food ComponentsProduct(s) of digestion
ProteinsAmino acids
FatsFatty acids and glycerol

Question 5: What are villi? What is their location and function?

The finger like projections in the inner walls of the small intestine is called villi.
These are found in small intestine.
Function: The villi increase the surface area for absorption of the digested food

Question 6: Where is the bile produced? Which component of the food does it help to digest?

Bile is produced in liver. The bile juice stored in sac called the gall bladder. It helps in the digestion of fats.

Question.7.  Name the type of carbohydrate that can be digested by ruminants but not by humans. Give the reason also.

Cellulose is the carbohydrate that can be digested by ruminants. Ruminants have large sac like structure between the small intestine and large intestine. The cellulose of the food is digested by the action of certain bacteria which are not present in humans.

Question.8. Why do we get instant energy from glucose?

We get instant energy from glucose because it easily breaks down in the cell with the help of oxygen which provides instant energy to the organism. Glucose does not need to go through the process of digestion; it is directly absorbed into the blood.

Question.9. Which part of the digestive canal is involved in:
(i) Absorption of food ________ .

Absorption of food Small intestine.

(ii) Chewing of food ________ .

Chewing of food Mouth.

(iii) Killing of bacteria ________ .

Killing of bacteria Stomach.

(iv) Complete digestion of food ________ .

Complete digestion of food Small intestine.

(v) Formation of faeces ________ .

Formation of faeces Large intestine.

Question.10. Write one similarity and one difference between the nutrition in amoeba and human beings.

Similarity: In both amoeba and human beings digestive juices break down the complex food particles into simpler substances that can be absorbed.
Difference: Amoeba has no mouth and no digestive system whereas human beings has a mouth and a complex digestive system made up of many organs.

Question.11. Match the items of Column I with suitable items in Column II.

Column 1Column 2
(a) Salivary glands(i) Bile juice secretion
(b) Stomach(ii) Storage of undigested food
(c) Liver(iii) Saliva secretion
(d) Rectum(iv) Acid release
(e) Small intestine(v) Digestion is completed
(f) Large intestine(vi) Absorption of water
 (vii) Release of faeces
Column 1Column 2
(a) Salivary glands(iii) Saliva secretion
(b) Stomach(iv) Acid release
(c) Liver(i) Bile juice secretion
(d) Rectum(v) Digestion is completed
(e) Small intestine(ii) Storage of undigested food
(f) Large intestine(vi) Absorption of water

Question.12. Label the below given figure of the Human digestive system.ScC2img09

Question.13. Can we survive only on raw, leafy vegetables/grass? Discuss.

We know that the animals, fungi, bacteria, non-green plants and human being do not have the ability to make their own food. They depend upon autotrophs or green plants for their food directly or indirectly. The green plant (leafy vegetables/grass) trap solar energy and make their own food in the form of glucose. So, we can say that leafy vegetables and grass can provide sufficient energy to help us survive.

Very Short Answer Type Questions

Question.1. What is ingestion?

The intake of food is called ingestion.

Question.2. What is digestion?

The breaking down of solid and complex food into simple and soluble forms is called digestion.

Question.3. What is absorption?

The process of passing of digested food into blood vessels in the intestine is called the absorption.

Question.4. What do you understand by assimilation?

The conversion of absorbed food in complex substances such as proteins and vitamins required by body is called assimilation.

Question.5. What do you understand by egestion?

Removal of waste materials from the body, time to time from anus is called egestion.

Question.6. What are the steps of nutrition involved in animals?

There is five steps of nutrition involved in animals. These are Ingestion, Digestion, Absorption, Assimilation and Egestion.

Question.7. What are Pseudopodia?

Finger-like outgrowths on amoeba are called pseudopodia.

(The word pseudopodia is the combination of pseudo and podus. Pseudo means false and podus means feet. Singular of pseudoposida is pseudopodium)

Question.8. How many types of teeth are found in human beings?

There are four types of teeth in human beings. These are called incisors, canines, premolars and molars.

Question.9. How many incisors are found in an adult human?

There are 8 incisors, 4 in lower and 4 in upper jaw, found in an adult human.

Question.10. What is the function of incisors?

Incisors are used to cut and bite the food.

Question.11. How many canines are found in an adult human?

There are four canine found in an adult human.

Question.12. What is the function of Canines?

Canines are the type of teeth, which help to hold and tear the food.

Question.13. How many premolars are found in an adult human?

There are 8 premolars found in an adult human.

Question.14. What is the function of premolars?

Premolars help in crushing and grinding the food.

Question.15. How many molars are found in an adult human?

There are 12 molars are found in an adult human.

Question.16. What is wisdom tooth?

Wisdom teeth are molar teeth that grow usually between the ages of 18 to 21 in an human. These are the last teeth to grow in human beings.

Question.17. How many teeth does a human adult have?

A human adult has 32 teeth in all: 16 teeth in each jaw.

Question.18. What do you understand by milk and permanent teeth?

Human has two sets of teeth. These are called milk teeth and permanent teeth. Milk teeth start growing at the baby stage and are replaced gradually by permanent teeth from the age of 8 year.

Question.19. What is Enamel?

The white substance that covers our teeth is called enamel. It is the hardest substance in the human body.

Question.20. What is a carnivorous animal? Give two examples.

Animals, which eat the flesh of other animals, are called carnivorous, e.g. lion, tiger.

Question.21. What is the function of the digestive juice secreted by the liver?

The digestive juice from the liver breaks up fat into tiny particles. This works in favor of easier digestion of fat.

Question.22. Name the organs that make up the alimentary canal.

Mouth, oesophagus, stomach, small intestine, large intestine and rectum compose the alimentary canal.

Question.23. Name the four types of teeth.

The four types of teeth are: Incisors, Canines, Premolars and Molars.

Question.24. Name the four compartments in a ruminant’s stomach.

Four compartments in a ruminant’s stomach are: Rumen, reticulum, omasum and abomasum.

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