Life Processes

02 Nutrition



  • Nutrition is a process of intake and utilization of nutrients by an organism.
  • Nutrition can be in the form of carbohydrates, fats, proteins, minerals, vitamins and water.
  • It is a vital process which helps living beings to obtain energy from various sources.
  • Nutrient is a substance which an organism obtains from its surrounding and uses it either as an energy source or for biosynthesis of body constituents.
  • The food consumed undergoes a lot of processing before the nutrients are utilized to generate energy.



There are mainly two modes of nutrition:

Autotrophic Mode of Nutrition:

  • Autotrophic mode of nutrition occurs when an organism makes their own food by photosynthesis.
  • The autotrophs take in food from simple inorganic materials like carbon dioxide and water present in the surroundings with the help of sunlight energy.
  • Those organisms which can make their own food from carbon dioxide and water are called autotrophs.
  • All the green plants are autotrophs that prepare their food by the process of photosynthesis.
  • The autotrophic bacteria also obtain their food by the autotrophic mode of nutrition.
  • Chlorophyll, a green pigment traps the sunlight energy. Chlorophyll is present in all the autotrophic organisms or autotrophs.



Heterotrophic Mode of Nutrition:

  • Heterotrophic mode of nutrition occurs when an organism cannot make (or synthesize) its own food from simple inorganic materials like carbon dioxide and water.
  • The heterotrophs depend on other organisms for its food.
  • All the animals have a heterotrophic mode of nutrition.
  • Most bacteria and fungi also have heterotrophic mode of nutrition.
  • The non-green plants (like yeast) are also heterotrophs.
  • Those organisms which cannot make their own food from inorganic substance like carbon dioxide and water, and depend on other organisms for their food are called heterotrophs.
  • Humans follow the holozoic mode of nutrition.



A heterotrophic organism or heterotroph obtains its food from other organisms in multiple ways. Hence, the mode of nutrition is classified into three ways:


Saprotrophic nutrition (or Saprophytic Nutrition):

  • In saprotrophic nutrition, the organism obtains its food from decaying organic matter of dead plants, dead animals and rotten bread.
  • In this mode of nutrition organism release some enzymes on dead and decomposing materials.
  • The enzymes break down them into simple nutrients which are absorbed by the organism as food.
  • For example: fungi and many bacteria are saprophytes.



Parasitic nutrition:

  • A parasite is an organism (plant or animal) which feeds on another living organism called host.
  • A parasite usually harms the host.
  • The host may be a plant or an animal.
  • Most of the diseases which affect mankind, his domestic animals (like dogs and cattle) and his crops are caused by parasites.
  • Some of the examples of Parasites are :
  • The micro-organism ‘plasmodium’ causes malaria disease)
  • Roundworm which causes diseases in man and domestic animals (like dogs and cattle)
  • Cuscuta (amarbel) which grown on mango are also parasites.
  • Some other examples of parasites are ticks, lice, leeches and tapeworms.



Holozoic Nutrition:

  • In this type of nutrition organism takes in whole material and breaks it down inside the body.
  • For example, animals eating grass, fruit, insects, fish etc.

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