Nutrition and mode of nutrition
What is nutrition?
Modes of nutrition:
There are four modes of nutrition and they are:
a) Autotrophic Nutrition
b) Heterotrophic Nutrition
The mode of nutrition through which an organism prepares its own food is called autotrophic nutrition. Plants follow autotrophic nutrition. It prepares its own food.
Green plants and blue-green algae follow the autotrophic mode of nutrition.
These organisms are called photosynthetic because they process raw materials in presence of sunlight to make food.
Some organisms process certain raw materials through chemical reactions, without utilizing the sunlight.
Heterotrophic nutrition is the mode of nutrition where the organism is unable to prepare its food and hence, depends upon plants or other organisms for nutrition.
Organisms, other than autotrophs, follow the heterotrophic mode of nutrition.
These organisms directly or indirectly depend on autotrophs for food.
Heterotrophic nutrition can be further divided into two types, viz. saprophytic nutrition and holozoic nutrition.
In saprophytic nutrition, the organism secretes digestive juices on food. The food is digested while it is still to be ingested. Digestion involves converting complex molecules into simple molecules so that they can be utilized by the organism.
The digested food is then ingested by the organism. All the decomposers follow saprophytic nutrition. Saprotrophs feed on dead remains of different organisms.
By doing so, they help in the decomposition of organic waste. This is an important process during various biogeochemical cycles. Many bacteria and all the fungi follow the saprotrophic mode of nutrition.
In holozoic nutrition, the digestion happens inside the body of the organism, i.e. after the food is ingested. Animals and protozoa follow this mode of nutrition.
In the next section, you will read how an amoeba (a protozoan) follows the holozoic mode of nutrition.