Nutrition is the ability of a living organism to feed while the chemicals taken in by the organism during this process is referred to as nutrients. Examples of these chemicals include Nitrogen, Carbon, Oxygen, Phosphorous, Hydrogen, and Chlorine to mention a few.Ingestion is the process of taking in the food substances into the body while egestion is the process of passing out of the undigested food particles from the body of a living organism through anus. Injection is the insertion of needle and syringe into the body.
Modes of Nutrition
All living organisms are capable of carrying out different modes of nutrition. However, the mode of nutrition can be group 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 can manufacture their 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: It 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 sunlight. This process is called Photosynthesis. The green plants derive their energy for making this food from the sunlight which is trapped by Chlorophyll. Examples of organisms that exhibit this process include flowering plants, Spirogyra, Euglena etc.
II. Chemosynthetic nutrition: It is another mode of nutrition in which certain bacteria are able to synthesize organic compounds from simple inorganic materials such as carbon dioxide, water, ammonia or nitrite to manufacture their food. The energy used for the synthesis comes from the oxidation of the inorganic materials or chemicals; hence the process is called Chemosynthesis, e.g. Nitrosomonas, Nitrobacter.
2. Heterotrophic nutrition: This is the type of nutrition in which the organisms cannot manufacture their foo but depend directly or indirectly on plants(autotrophs) for their food. Organisms which cannot manufacture their food are called heterotrophs. Most animals, fungi, protozoa and some bacteria belong to this group.
I. Holozoic nutrition: This involves the feeding on other organisms or solid organic substances synthesized by green plants. The organisms ingest, digest and assimilate these food substances into their bodies. 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 plants
(c) Omnivores like man, pig etc. that feed on both flesh and plants/vegetables
d. Scavengers like vultures that feed on dead animals
II. Parasitic nutrition: This is the type of nutrition in which certain organisms feed on another organism in order to derive nourishment from it. This mode of nutrition is called parasitic nutrition while the association is called Parasitism. Parasitism is an association between two organisms, usually of different species in which one called the parasite gains from the association while the other called the host is harmed or suffered losses. Examples include Tapeworm, plasmodium, ticks, bugs, dodder (plant), mistletoe (plant) etc.
Animal parasites are classified as endoparasites and ectoparasites.
I.Ectoparasites:- These are parasites which live on (outside) the body of their hosts where they derive food and shelter from e.g. flea, bedbug, and tick.
II. Endoparasites:- These are parasites which live inside the body of their hosts such as man and other animals. Examples include Tapeworm (host- pig and man), Liverfluke (Fasciola hepatica, host – sheep), Filaria (Wucheraria brancrofti, host – cattle, sheep and goat), Guinea worm (Drancunculus medinensis).
