0Amoeba is a holozoic and protozoan. The digestion is intracellular as it is a unicellular organism. The food taken remains in a food vacuole or gastric vacuole formed by the cell membrane and a bit of the cytoplasm. The vacuoles are transported deeper into the cells by cytoplasmic movements. Here they fuse with lysosomes that contain enzymes such as amylase and proteinase. Thus, amoeba can digest sugar, cellulose and protein. Fats, however, remain undigested.
Nutrition in Amoeba:-
Food - Amoeba is a holozoic and omnivorous animal. It feeds upon microscopic organisms like bacteria, Paramecium, Diatoms, Algae and dead organic matter.
Nutrition in Amoeba involves the following steps:
(i) Ingestion:- Amoeba has no mouth so ingestion may occur at any point of body surface but generally it occurs at the advancing end of the body. Ingestion occurs with the help of pseudopodia. The opening of food cup gradually becomes narrower and narrower, and finally closes. So the food is finally enveloped and taken inside a food-vacuole (called phagosome) along with a drop of water.
(ii) Digestion:- Amoeba shows intracellular and vacuolar digestion. In the cytoplasm, food vacuole fuses with lysosomes containing digestive enzymes. In this, the complex and non-diffusible nutrients are changed into simple and diffusible nutrients. Medium inside the food vacuole is first acidic but later becomes alkaline, (as in the alimentary canal of man).
(iii) Absorption:_ In absorption, the diffusible nutrients pass through the vacuolar membrane into the cytoplasm by diffusion and are then distributed to all the body parts by streaming movements of cytoplasm called cyclosis. Due to this, the size of food vacuole gradually decreases.
(iv)Assimilation: In the cytoplasm, a part of the absorbed food is oxidised to produce energy, most of the simple nutrients are combined to synthesise complex compounds. Thus, the absorbed food materials are utilised to get energy through respiration and make the different parts of Amoeba cell and it leads to the growth of Amoeba.
(v) Egestion: Egestion may occur at any point on the body surface.
