Intake of food, digestion of food, absorption of digested food materials and elimination of undigested waste materials are included in nutrition.
Toad is a carnivorous animal. The main food of toad is live worms, insects, earth worms, snails etc. With the sticky tongue, it catches the prey and swallows it. Like all vertebrate animals, in the food of toad protein, carbohydrate, fat, salt, vitamins and water components are present. These six types of components can be obtained from the bodies of worms and insects. It is not required to digest salt, vitamins and water.
The cells of the body of toad can directly absorb these three types of food. But protein, carbohydrate and fat are complex organic substances; hence the body cells cannot absorb them directly. In the presence of enzymes, these insoluble, complex and non-absorbable food substances take part in organic chemical reactions and transform into simple and absorbable liquid components. These changes of food substances are called digestion.
After the intake of the food, there are no chemical changes inside the buccal cavity. The food substances become slippery by the mucus secreted from the walls of the buccal cavity. Food substances reach the stomach through the oesophagus where digestion begins.