What are the two important Modes of Nutrition?

Modes of nutrition mean methods of procuring food or obtaining food by an organism. All the organisms do not obtain their food in the same way. Different organisms have different methods of procuring food or obtaining food. In other words, organisms differ in their modes of nutrition. Depending on the mode (or method) of obtaining food, all the organisms can be classified into two groups: autotrophic and heterotrophic. Thus: There are mainly two modes of nutrition:

1. Autotrophic, and

2. Heterotrophic.

We will now discuss the autotrophic mode of nutrition and the heterotrophic mode of nutrition in detail, one by one.

1. Autotrophic Mode of Nutrition:

The word ‘auto’ means ‘self’ and ‘trophe’ means ‘nutrition’. Thus, autotrophic means ‘self nutrition’. In autotrophic nutrition, the organism makes (or synthesizes) its own food from the inorganic raw materials I like carbon dioxide and water present in the surroundings by using the sunlight energy.

We can now say that: Autotrophic nutrition is that mode of nutrition in which an organism makes (or synthesizes) its own food from the simple inorganic materials like carbon dioxide and water present in the surroundings (with the help of sunlight energy). Please note that food is an organic material (like glucose, etc.).

This means that, in autotrophic nutrition; organic material (food) is made (or synthesized) from inorganic materials like carbon dioxide and water by utilizing the sunlight energy. The green plants have an autotrophic mode of nutrition. The autotrophic bacteria also obtain their food by the autotrophic mode of nutrition (though most bacteria are not autotrophic). The organisms having autotrophic mode of nutrition are called autotrophic organisms or just autotrophs.

Those organisms which can make their own food from carbon dioxide and water are called autotrophs.

Carbon dioxide and water are inorganic substances. So, we can also say that: Those organisms which can make their own food from the inorganic substances present in the environment, are called autotrophs.

All the green plants are autotrophs (because they can make their own food from inorganic substances like carbon dioxide and water present in the environment). Non-green plants are, however, not autotrophs. Certain bacteria called ‘autotrophic bacteria’ are also autotrophs.

The autotrophic organisms (or autotrophs) contain the green pigment called chlorophyll which is capable of trapping sunlight energy. This trapped sunlight energy is utilised by the autotrophs to make food by combining inorganic materials like carbon dioxide and water present in the environment by the process of photosynthesis.

Thus, autotrophs make their own food by photosynthesis. So, autotrophs are the producers of food. The food produced by autotrophs (green plants) is also used by human beings and many, many other animals.

2. Heterotrophic Mode of Nutrition :

The word ‘heteros’ means ‘others’ and ‘trophe’ refers to ‘nutrition’. Thus, ‘heterotrophic’ means ‘nutrition obtained from others’. In heterotrophic nutrition, the organism cannot make (or synthesize) its own food from the inorganic raw materials like carbon dioxide and water, and uses the food made by autotrophic organisms directly or indirectly We can now say that: Heterotrophic nutrition is that mode of nutrition in which an organism cannot make (or synthesize) its own food from simple inorganic materials like carbon dioxide and water, and depends on other organisms for its food.

A heterotrophic organism is a consumer which derives its nutrition from other organisms. That is, a heterotrophic organism has to eat other organisms for its nutrition. All the animals have a heterotrophic mode of nutrition. Most bacteria and fungi also have heterotrophic mode of nutrition. The organisms having heterotrophic mode of nutrition are called heterotrophic organisms or just heterotrophs.

Those organisms which cannot make their own food from inorganic substances like carbon dioxide and water, and depend on other organisms for their food are called heterotrophs. All the animals are heterotrophs (because they cannot make food from inorganic substances like carbon dioxide and water and obtain their food from other plants or animals.).

Thus, man, dog, cat, deer, tiger, bear, lion, cow, etc., are all heterotrophs. The non-green plants (like yeast) are also heterotrophs. Heterotrophs depend on autotrophs and other heterotrophs for their food. In other words, animals are heterotrophs which depend on plants or other animals for their food.

From the above discussion we conclude that green plants make their own food. Non-green plants and animals cannot make their own food. They obtain food from plants and other animals. We will now discuss the various types of the heterotrophic mode of nutrition.