CBSE – 7th Standard Science

Chapter 2 – Nutrition in Animals


Nutrition in Animals

  • Plants can prepare their own food by photosynthesis but Animals
  • All organisms including humans require food for growth, repair and functioning of the body.
  • Animals nutrition includes nutrient requirement, mode of intake of food and its utilisation in the body.
  • The breakdown of complex components of food like carbohydrates into simpler substances is called
  • For digestion in humans, the food passes through a continuous canal consisting of several digestive organs and glands.
  • The digestive tract and the associated glands together constitute the digestive system.
  • Glands secrete digestive juice which converts complex substance of food into simpler ones.
  • The canal can be divided into various compartments as – buccal cavity, food pipe or oesophagus, stomach, small intestine, large intestine, rectum and anus.
  • Food is taken into the body through the mouth.
  • The process of taking food into the body is called ingestion.
  • The swallowed food passes into food pipe.
  • Food pipe runs along the neck and chest.
  • Food is pushed down by movement of the wall of food pipe.
  • Stomach is a thick-walled flattened U shaped bag.
  • The inner lining of stomach secretes mucous, hydrochloric acid and digestive juices.


  • Small intestine is highly coiled and is about 7.5 m long.
  • Small intestine receives secretions from liver and the pancreas.
  • Here, carbohydrates get broken into simple sugars such as glucose, fats into fatty acids and glycerol and proteins into amino acids.
  • The absorption of digested food into blood vessels takes place through thousands of fingers like outgrowth called villi.



  • LIVER– It is situated in upper part of the abdomen. It is the largest gland in the body.


  • It secretes bile juice which is stored in a sac called gall bladder.
  • Bile plays an important role in digestion of fats.
  • The food that remains undigested enters into large intestine.
  • Its function is to absorb water and some salts from undigested food material.
  • The remaining waste passes into the rectum and remains there as semi-solid faeces.
  • The faecal matter is removed through the anus. This is called egestion.
  • The grazing animals like cows, buffaloes and deer are known as Ruminants.


  • They quickly swallow the grass and store it in part of stomach called Rumen.
  • The swallowed food returns to mouth and the animal chews it. This process is called Rumination.
  • Amoeba is a microscopic single-celled organism.
  • It moves and captures the food by pushing out one or more finger like projections called Pseudopodia or False feet.


  • The food becomes trapped in the food vacuole.
  • Absorbed foods are used for growth, maintenance and multiplication.
  • The undigested food is expelled outside by the vacuole.
  • Animal nutrition includes nutrient requirement, mode of intake of food and its utilization in the body.
  • Human digestive system consists of alimentary canals and secretory glands. It consists of buccal cavity, oesophagus, stomach, small intestine and large intestine ending in rectum and anus.
  • The main digestive glands which secrete digestive juices are salivary glands, liver and pancreas.
  • Nutrition is a complex process involving ingestion, digestion, absorption, assimilation and egestion.
  • The absorbed substances are transported to different parts of the body and the undigested residues are expelled out of the body as faeces through the anus.
  • Starfish feeds on animals covered by hard shells of calcium carbonate.
  • After opening the shell, the starfish pops out its stomach through its mouth to eat the soft animal inside the shell.
  • The stomach then goes back into the body and the food is slowly digested.
  • The first set of teeth grows during infancy and they fall off at the age between six to eight years.


  • These are termed milk teeth. The second set that replaces them are the permanent teeth.
  • The permanent teeth may last throughout life or fall off during old age or due to some dental disease.
  • Normally bacteria are present in our mouth but they are not harmful to us.
  • However, if we do not clean our teeth and mouth after eating, many harmful bacteria also begin to live and grow in it.
  • These bacteria break down the sugars present from the leftover food and release acids (see Chapter 5 to know what an acid is).
  • The acids gradually damage the teeth This is called tooth decay.
  • If it is not treated in time, it causes severe toothache and in extreme cases results in tooth loss.
  • Chocolates, sweets, soft drinks and other sugar products are the major culprits of tooth decay.
  • Therefore, one should clean the teeth with a brush or datun and dental floss (a special strong thread which is moved between two teeth to take out trapped food particles) at least twice a day and rinse the mouth after every meal.
  • Also, one should not put dirty fingers or any unwashed object in the mouth.