1.Ingestion:In this process food is taken inside by the organisms. Excepting a few (Spiders, mosquitoes, flies which suck in liquid food), all animals consume solid food. Different organs are involved in different animals for this purpose. Amoeba, a unicellular organism can take the food from surface of its body. In Hydra, the food is ingested with the help of tentacles. There are well-developed organs and methods to take food in vertebrates like lizards, birds and mammals.
The acquisition and ingestion of food is collectively termed feeding. Depending upon the nature of food, feeding may be of three types in animals.
(a) Microphagy:
It involves the feeding of particles which are small in comparison to the size of the organism. Paramecium, sponges, crustaceans, snails, certain fishes and birds, blue whales, etc. show microphagy. In this method water passes through filters. The contained food particles are retained and uti9lised. This method is hence, known as filter feeding.
(b) Macrophagy:
It involves the feeding of particles which are large in comparison to the size of the organism, Amoeba, Hydra, certain amphibians, reptiles, fishes and birds show such type of feeding. They swallow the food as a whole without chewing.
(c) Liquid feeding:
It is also known as fluid-feeding. Leeches, tape-worm, bats, mosquitoes, be bugs, spiders, flies and mil-sucking young mammals are the examples of this type. The foods engulfed or captured by most of the mammals are mechanically broken into smaller pieces. Teeth, jaw bones and muscles help them in doing this work.
In the animals which feed on plant (herbivores) like-horse, sheep, cow, the premolar and molar teeth have well developed ridges for effective grinding of the food. In the animals which feed on other animals (carnivores) like tiger, cat, dog, leopard, the canine teeth are sharp and large for terracing the flesh.
2. Digestion: Food is digested within the cell in unicellular organisms like Amoeba. This process is termed intracellular digestion. In multi-cellular organisms too, digestion can take place inside the cell, for example, in Hydra. But digestion in multi-cellular organisms takes place in a long tube celled the elementary canal. As against the word 'intracellular', the expression extracellular digestion can be used for the digestion taking place in the mouth or in elementary canal. 3. AbsorptionIn this process the soluble parts of the food form the digestive region are absorbed across a membrane into the blood vessels. 4. AssimilationThe absorbed food material is utilized by the body to provide energy. 5. EgestionIt is process by which the insoluble parts of the food are discharge from the body of the animal as faeces.
