The Digestive Systems

The Digestive Systems

The digestive systems works on nutrients taken from the environment, breaking them down into simpler
products, and then absorbing the products together with water and salts so they can be used in metabolism.

The individuals of all species contain many different protiens or carbohydrates in the cell walls of
bacteria, chitin in the external skeletons of arthropods, and so on and foreign proteins or carbohydrates are
rarely incorporated unchanged. They are usually first broken down to their constituents before being built
up again as the proteins or carbohydrates belonging to the organism.

In such organisms that are not cellular as amoebae, digestion occurs inside the cell. Intracelular
digestion is also found in some higher animals such as mussels and sponges. Muscles, for instance, filter
algae and other tiny organisms from the water and digest them within the cells of a special digestive gland.
Intracellular digestion occurs even in some animals that consume large pieces of food; the prey captured by
Hydra, for example, is partly digested in the coelenteron, a gut-like cavity, and the residue is completely
digested in cells of the body wall. Scientists believe that intracellular digestion in organisms such as Hydra
has evolved from such protozoans as amoebae and paramecia.

In most higher animals digestion is completed not in the cell in the cavity of a digestive tract (the
stomach and intestine). Animals with this type of digestion in...

The Digestive Systems

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