Modes Of Nutrition
All living organisms are capable of carrying out different modes of nutrition. However, the mode of nutrition can be grouped into two major classes referred to as autotrophic and heterotrophic nutrition.
1. Autotrophic Nutrition
This is the type of nutrition in which organisms are able to manufacture their food. Organisms which manufacture their own food are called autotrophs
Autotrophic nutrition is further divided into two groups. These are holophytic or photosynthetic nutrition and chemosynthetic nutrition.
i. Holophytic (Photosynthetic) Nutrition: Holophytic nutrition is the type of nutrition in which all green plants are able to manufacture their own food making use of carbon dioxide and water in the presence of light. This process is called photosynthesis. Popular examples of organisms that carry out or exhibit photosynthetic nutrition are all green plants such as flowering plants, Spirogyra, Euglena, blue-green alga (nostoc) etc.
ii. Chemosynthetic Nutrition: Chemosynthetic nutrition is another mode of nutrition in which certain bacteria are able to synthesise organic compounds from simple inorganic materials such as carbon (iv) oxide, ammonia, water or nitrite to manufacture their own food. Hence the process is called Chemosynthesis. Examples of organisms or bacteria that exhibit chemosynthetic nutrition are: Nitrosomonas, Nitrobacter etc.
2. Heterotrophic Nutrition
This is the type of nutrition in which organisms cannot manufacture their food but depend directly or indirectly on plants (autotrophs) for their food. Organisms which cannot manufacture their food. Organisms which cannot manufacture their food are called heterotrophs Most animals, fungi, protozoa and some bacteria belong to this group.
Heterotrophic nutrition is also sub-divided into the following groups or types:
i. Holozoic nutrition: Holozoic nutrition involves the feeding on other organisms or solid organic substances synthesised by green plants. Examples of organisms that exhibit holozoic mode of nutrition are:
a. Carnivores like cats, dogs, lions etc that feed on flesh.
b. Herbivores like sheep, goats, rabbits etc that feed on plant.
c. Omnivores like man, pig etc that feed on both flesh and vegetables or plants.
d. Scavengers like vulture that feed on dead animals.
ii. Parasitic Nutrition: This is the type of nutrition in which certain organisms feed on another organismin order to derive nourishment from it. Examples are:
a. Animals like tapeworm, plasmodium, roundworms, leeches, aphids, ticks etc.
b. Plants parasites like Dodder and mistletoe.
iii. Symbiotic Nutrition: This is the type of nutrition in which two organisms of different species called symbionts live together and derive nutrients or food from each other. Examples are algae and fungi in a linen, etc.