Ans.
Collar cells or choanocytes are specialized cells, which are found in sponges and help them in digestion. The collar cells generate a water current through the organisms and to catch and ingest the food particles, by the process of phagocytosis.
Digestion of food takes place inside the collar cells, where lysosomes get fused with food vacuole. Lysosomes contain many digestive enzymes that help in digestion of complex food particles into simpler food molecules.
Thus, the correct words to be filled in the given blanks are 'phagocytosis' and 'lysosomes', respectively.
