digestive system lab

• Sponges lack complex digestive, respiratory, circulatory, and nervous systems.
• Sponge food is trapped as water passes through the ostia and out through the osculum. Bacteria smaller than 0.5 microns in size are trapped by choanocytes, which are the principal cells engaged in feeding, and are ingested by phagocytosis. 
• All other major body functions in the sponge (gas exchange, circulation, excretion) are performed by diffusion between the cells that line the openings within the sponge and the water that is passing through those
• intracellular digestion: a form of digestion which takes place within the cytoplasm of the organism takes place in animals without a digestive tract, in which food items are brought into the cell for digestion
• extracellular digestion: a process in which animals feed by secreting enzymes through the cell membrane onto the food
• The enzymes break the food into molecules small enough to be taken pass through the cell membrane into the cell. These nutrients are transferred into the blood or other body fluids and distributed to the rest of the body