Every organism needs a continuous supply of metabolites
for growth and energy to function normally in life. Most organisms
get both metabolites and energy from the food they
consume.
Food is the first requisition of the process
of nutrition. It is essential for several purposes :
-
It provides metabolites or building material
for the body of an organism.
-
It constitutes a source of energy for the organism.
-
It also helps in the normal functioning and
well balanced growth of the body.
-
It compensates for the wear and tear of the
body.
The process in which food is obtained, prepared,
absorbed and converted into body substances, is called nutrition.
It is the main life-sustaining process in an organism: it
provides the raw materials for the maintenance of life.
Nutrition in animals occurs in five phases namely
(i) feeding or ingestion, (ii) digestion
(iii) absorption and (iv) assimilation.
-
Ingestion is the process of taking
in food.
-
Digestion is the process of breaking
up complex substances into simpler substances.
-
Absorption is concerned with diffusion
of digested food into blood and lymph.
-
Assimilation is the conversion or
incorporation of absorbed simple food into the complex substances
constituting the body.
-
Egestion is the elimination of
undigested food from the body.
Figure 16.1 Nutrition in higher animals
