Ans.3. 1. Food : Sycon (sponges) feeds on minute organisms such as bacteria, diatoms and protozoans and other organic particles in water.
2. Feeding: Food enters inside sponge body along with water current through ostia. When water current passes through the flagellated chambers, the food picked up by choanocytes in either of the two ways:
(a) Food particles adhere to the outer surface of collar of choanocytes and are taken in, or
(b) Food particles are caught between the collars and are passed into the cytoplasm of choanocytes.
3. Digestion: The digestion of food might occur either inside the choanocytes, or is passed on to distribute the digested food from cell to cell. In any case, the digestion is intracellular occurring inside the food vacuoles.
The food vacuoles are at first acidic and become alkaline later on. The enzymes are secreted from the surrounding cytoplasm. Several enzymes such as trypsin, pepsin, rennin, lipase, invertase and amylase have been detected.
4. Assimilation: The digested food is distributed from cell to cell by the wandering amoebocytes found in mesenchyme. The digested food is stored as glycogen, fat, etc., in the amoebocytes.
5. Egestion : The undigested food residue is egested out from the amoebocytes into the outgoing water current and expelled out of the body.