hii niharika
Amoeba is a microphagous feeder, which means that it feeds upon small aquatic organisms like bacteria, flagellates, ciliates and minute food particles.
When a hungry Amoeba approaches to some food particle, it produces out its pseudopodia in the form of food cup which engulf the food particle by turning into food vacuole. the food also contain some water. this complete ingestion. the next step is digestion which is faciliated by the lysosomes. A few lysosomes surround the food vacuole and get fused with the membrane to discharge their enzymatic contents(proteases, amylases and lipases)into it. Hence the digestion is intacellular. At this stage the vacuole becomes a digestive vacuole. It decrease in size as the water is withdrawn and its content first become acidic(pH 5.6) and then alkaline. When the digestion is completed, the digestive vacuole membrane is drawn into numerous fine canals. the soluble food particles are passed into the canals and finally into the surrounding cytoplasm by micropinocytosis. the digested food, water and minerals are absorbed(absorption) into the cytoplasm and circulate in it, through cyclosis where the food is assimilated into new protoplasm or is oxidized to librate energy. the undigested food is egested by exocytosis at the rear end.