Which one of the following cells maintain a current of water in sponge ?

Question

Accepted Answer

The correct option is 4: Choanocyte

The single-most important cellular component that powers the entire life support system of a sponge—the water current—is the Choanocyte, also famously known as the collar cell. These highly specialized cells line the internal chambers and canals of the sponge's complex aquiferous system. Each choanocyte is equipped with a single, long, whip-like flagellum whose powerful, rhythmic, and coordinated beating acts as a microscopic propeller, creating the low-pressure zones that draw water into the sponge through the dermal pores (ostia). Surrounding the base of the flagellum is a delicate ring of microvilli called the 'collar,' which functions as a fine sieve. As the water current flows past, this collar traps minute food particles, which are then engulfed by the cell body. Therefore, the choanocytes are not merely responsible for feeding, but their flagellar action is the fundamental engine that maintains the continuous flow of water necessary for respiration (gas exchange), waste removal, and reproduction. Without the tireless beating of the choanocyte flagella, the sponge would cease to function and quickly perish.

The incorrect option is 1: Porocyte

The Porocyte is a tubular, cylinder-shaped cell that is found embedded in the pinacoderm, which is the outer layer of the sponge body. In the simplest sponge type (Asconoid), a single porocyte forms a channel known as an *ostium* or incurrent pore, allowing water to pass from the exterior directly into the central cavity (spongocoel). While porocytes are structurally essential for the *entry* of water, their function is to act as a fixed, passive conduit. They are not ciliated or flagellated and therefore possess no contractile or propulsive mechanism to actively *generate* or *maintain* the flow of water that passes through them. The current that flows through the porocyte is solely established by the beating action of the choanocytes elsewhere in the sponge body.

The incorrect option is 2: Myocyte

Myocytes are contractile cells that resemble muscle cells (hence the root 'myo'). They are typically found arranged in rings or bands around the main water openings, such as the *osculum* (the excurrent opening) and sometimes around the *ostia*. Their function is to constrict or dilate these openings, allowing the sponge to regulate the overall rate of water flow passing in and out of its body. For example, a sponge may contract its myocytes to narrow the osculum if the water contains excessive sediment or is flowing too rapidly. However, just like porocytes, myocytes are not flagellated. Their role is purely regulatory and contractile—they control the *aperture* of the water flow, but they do not possess the necessary machinery to *create* the current itself.

The incorrect option is 3: Chromocyte

Chromocytes are a type of amoeboid cell, meaning they are motile and irregularly shaped, found within the mesohyl (the jelly-like matrix between the outer and inner cell layers). As their name suggests, they are pigment-containing cells that are responsible for giving the sponge its specific color, which can vary widely in nature. Their function is related to coloration and possibly UV protection, serving a largely aesthetic or protective role. Chromocytes have no direct involvement in the maintenance of the aquiferous system. They do not possess flagella, nor are they strategically positioned near the pores or canals to influence the current. Thus, they are essential for the sponge's visual characteristics but completely separate from its water-pumping mechanism.