AL M NTARY

CANAL

A UNIQUE MACROMOLECULE

SPLITTING TOOL

Every organism requires energy for his various metabolic processes, which is obtained from food. Food is taken into the

alimentary canal, where it is digested and assimilated. The alimentary canal begins at the mouth, passes through the thorax,

abdomen, pelvis and ends at the anus. It has a general structure, which is modified at different levels in different organisms to

provide maximum benefit for the processes occurring at each level. This article is an effort to provide a collective information

about the diversity of this canal in synchronised manner.

The complex digestive processes in organisms are

necessary to simplify the food eaten until they are in a

form suitable for absorption. Macromolecules of food

therefore goes through a series of changes, which

releases their constituent nutrients, i.e., amino acids,

mineral salts, fat and vitamins. Chemical substances or

enzymes, which affect these changes are secreted into

the digestive or alimentary canal by special glands. Some

glands are found in the walls of this canal and some

outside the canal, but with ducts leading into it.

Diversity in Digestive Structures

of Invertebrates

In primitive multicellular organisms, such as cnidarians,

the gut is a blind (closed) sac called gastrovascular

cavity. They have an incomplete digestive tract

with a single opening.

Some specialised cells in the cavity secrete digestive enzymes

that begin the process of extracellular digestion. Other

phagocytic cells that line the cavity engulf food material and

continue intracellular digestion inside food vacuoles. Some

flatworms have similar digestive patterns.

Here we will discuss about

 the digestive system of a ciliated protozoan (intracellular

digestive system),

 digestive system of an insect (extracellular digestive

system with a complete digestive tract),

 digestive system of the bivalve mollusc (intracellular and

extracellular digestion).

Protozoa

 Protozoans may be autotrophic, saprozoic or heterotrophic.

Ciliated Protozoa utilise heterotrophic nutrition.

 Cilia direct food toward the cytostome (mouth). The food

enters the cytopharynx.

 In cytopharynx a food vacuole forms and detaches from it.

Dr. Anamika Tripathi