Short Notes: NUTRITION

The basic functions performed by living organisms to maintain their life on this earth are called life processes.

Basic life process if common for all living beings.

NUTRITION Taking of food inside the body and converting it into smaller molecules which can be absorbed by the body.
RESPIRATION The process which releases energy from the food absorbed by the body.
TRANSPORT The process in which a substance absorbed or made in one part of the body is moved to other parts of the body.
EXCRETION The process in which the waste materials produced in the cells of the body are removed from the body.
  • All the living organisms need energy to perform various life processes. They get this energy from food. Food is a kind of fuel which provides energy to all the living organisms. This leads us to discussion of nutrition first.



  • Food is an organic substance. The simplest food is glucose also called simple sugar.
  • A more complex food is starch. It is made from glucose.
  • The general name of substances like glucose and starch is ‘carbohydrates’.

Difference between nutrient and nutrition!



A nutrient can be defined as a substance which an organism obtains from its surroundings and uses it as a source of energy or for the biosynthesis of its body constituents. Nutrition is the process of intake of nutrients (like carbohydrates, fats, proteins, minerals, vitamins and water) by an organism as well as the utilization of these nutrients by the organism.

Modes of Nutrition

  1. Autotrophic mode of nutrition  : “self-nutrition”
  2. Heterotrophic mode of nutrition  “others-nutrition”

Heterotrophic mode of nutrition is further divided in 3 categories as:

  1. Saprotrophic (saprophytic) nutrition
  2. Parasitic nutrition
  3. Holozoic nutrition

Nutrition in Animals

  • Animals are heterotrophs and hence they depend on other organisms (plants and other animals) for their food.
  • All the animals can be divided into three groups on the basis of their food habits. These are:
  1. Herbivores
  2. Carnivores
  3. Omnivores

Different steps in the process of nutrition in animals

There are five steps in the process of nutrition in animals.

  1. Ingestion: The process of taking food into the body is called ingestion.
  2. Digestion: the process in which the food containing large, insoluble molecules is broken down into small, water soluble molecules is called digestion.
  3. Absorption: The process in which the digested food passes through the intestinal wall into blood stream is called absorption.
  4. Assimilation: The process in which the absorbed food is taken in by the body cells and used for energy, growth and repair is called assimilation.
  5. Egestion: The process in which the undigested food is removed from the body is called egestion.

Nutrition in Simple Animals:

Amoeba and paramecium are two very simple unicellular animals. In unicellular animals, all the processes of nutrition are performed by the single cell.

Nutrition in Amoeba:

  • Amoeba 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.

    Nutrition in Human Beings:

      • The various organs of the human digestive system in sequence are: Mouth, Oesophagus (Food pipe), Stomach, Small intestine and Large intestine.
      • The glands which are associated with the human digestive system are: Salivary glands, Liver and Pancreas.


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