Question

In the most simple type of canal system of Porifera, water flows through which one of the following ways?
A. Ostia $\rightarrow$ Spongocoel $\rightarrow$ Osculum $\rightarrow$ Exterior
B. Spongocoel $\rightarrow$ Ostia $\rightarrow$ Osculum $\rightarrow$ Exterior
C. Osculum $\rightarrow$ Spongocoel $\rightarrow$ Ostia $\rightarrow$ Exterior
D. Osculum $\rightarrow$ Ostia $\rightarrow$ Spongocoel $\rightarrow$ Exterior

Answer 1

Hint: Porifera are the group of multicellular organisms which are chiefly aquatic in nature. They bear specialized cells that are capable of transforming into several other types of cells when needed. The peculiar features of the Porifera are the presence of numerous pores in the body which allows passage of water.

Complete answer:
Porifera are aquatic, multicellular organisms and are commonly known as sponges. These are sessile organisms that bear bodies perforated by a large number of pores. The pores or the channels allows the movement of water through them. The sponges consist of jelly like mesohyl that lies between the two layers of the cell. In sponges, there are no distinct and complex systems such as nervous system, digestive system or circulatory system. The different biological processes of the animal depends upon the passage and constant flow of water through their bodies. The water inlet and outlets are connected by an arrangement of chambers that are lined with cells.

The pores present on the bodies of the sponges are known as ostia. The ostia leads to the interior of the body of the sponges through the mesohyl layer. The water flow pattern of sponges can be compared with the chimneys. The water enters through the body pores or the ostia and is ejected out through a single large opening known as the osculum. The osculum is also known as the mouth of the sponge. After the entry of water through the ostia, it enters the central cavity of the sponge. The central cavity is known as the spongocoel.

The spongocoel can be a simple type of cavity in some sponges and may be a complex type and it depends on the body plan of the sponge. The spongocoel is lined by special types of cells that are known as the choanocytes. These cells bear a whip-like flagella and it helps to push the water through the spongocoel through their synchronized beating movements.

The water from the central cavity then moves towards the largest opening present at the top of the sponge. The large opening is an excretory pore and called as the osculum. The osculum opens to the outside through which the water is expelled out of the body. The water expelled through the osculum to the exterior of the sponge is called an excurrent system.

Hence, The correct answer is option (A).

Note: Sponges are aquatic organisms and bear several pores on the body which are known as ostia. Through the ostia, the water enters the body of the sponge and moves towards the spongocoel or the central cavity of the sponges. The water is then moved to the osculum and it is expelled to the exterior environment. The sponges are sessile organisms so they depend on the flow and current of water to supply food materials and to remove the waste materials from the body.