Question

Explain how digestion occurs in sponges.

Short answer

Digestion in sponges occurs through a process involving the structure and organization of the sponge, the role of choanocytes, ingestion of food particles, intracellular digestion, and egestion of waste products. Sponges are filter feeders that draw in water through their pores and capture food particles using specialized flagellated cells called choanocytes. These cells ingest the food particles into food vacuoles, where intracellular digestion takes place, and the nutrients are absorbed and transported to other cells within the sponge. Waste products are then released by the choanocytes into the surrounding water and flushed out of the sponge through the osculum.

Step-by-step solution

1. Structure and organization of a sponge

Sponges (Phylum Porifera) are simple, sessile marine animals that lack true tissues and organs. They have a porous structure made up of a few cell types, primarily including choanocytes, which play a significant role in the digestive process. The body of a sponge consists of an outer dermal layer, an inner layer called the choanoderm, and a central cavity called a spongocoel. The pores or ostia on the surface lead to a system of canals, which are lined with choanocytes.

2. Role of choanocytes in digestion

Choanocytes, also known as collar cells, are specialized flagellated cells that line the inner canals and chambers of a sponge's body. They have a thin collar surrounding a single flagellum, which creates water currents when the flagella beat. Choanocytes are responsible for filtering food particles from the water and initiate the process of digestion.

3. Ingestion of food particles

Sponges are filter feeders, which means they obtain their nutrients by filtering water through their porous bodies. The beating of flagella from choanocytes creates a steady flow of water through the sponge's canal system, entering into the ostia and exiting through the osculum. As the water passes through the canals, tiny food particles such as bacteria, plankton, and organic matter are trapped by the collar of choanocytes and ingested into the cell.

4. Intracellular digestion process

Once the food particles are ingested, they are enclosed within a food vacuole inside the choanocyte. The intracellular digestion of food particles occurs within these food vacuoles, where enzymes are secreted to break down the nutrients. The digested nutrients are then absorbed by the choanocyte and transported to other cells within the sponge's body.

5. Egestion of waste products

Waste products from digestion, such as carbon dioxide and other excretory materials, are released by the choanocytes into the surrounding water. This process of eliminating waste products is called egestion. The water current generated by the choanocytes continuously flushes waste products out of the sponge through the osculum, maintaining a clean environment and providing a continuous supply of nutrients for the sponge.