Cell Functions of a Sponge

Sponges are invertebrates--animals without backbones. A simple kind of sponge looks like a narrow-mouthed vase. It consists of two layers of cells with a jelly-like region called mesohyl in between. The center of the sponge is a hollow area called the spongocoel. There is a large opening called an osculum at one end, and little pores called ostia lie on the sides. The cells of the sponge form a loosely organized unit. There are different kinds of cells, each with its own specialized function.

  1. Water Circulation

    • Choanocytes are cells with whip-like structures called flagella. By an undulating movement of the flagella, the choanocytes set up a current of water. The water enters the sponge through the pores, proceeds through the spongocoel and exits through the osculum.

    Trapping Food

    • Sponges attach themselves to a suitable surface on the ocean floor. They cannot move about to find food, but the water current generated by the choanocytes draws tiny plants and animals collectively called plankton into the sponge. The choanocytes have funnel-shaped membranes called collars at the foot of their flagella, which trap this nourishing plankton. The choanocytes eat as much of this plankton as they need by a process called phagocytosis.

    Transporting Food

    • In the mesohyl between the two layers of cells in the sponge's body are cells capable of independent movement called amoebocytes. These amoebocytes crawl to the collars of the choanocytes, remove the extra food that is stuck there, eat what they need and transport the rest to the other cells on the outer layer of the sponge's body.

    Producing Skeletal Material

    • The amoebocytes also produce a tough substance that gives a measure of rigidity to the sponge's body. In some species, the amoebocytes produce spongin, which is the substance that people use in natural kitchen sponges. In other species, the amoebocytes produce a glass-like substance. Still others secrete a calcium carbonate skeleton.

    Sensing Stimuli

    • The sponge possesses no nervous system, but each cell receives sensations independently, according to the book "Biology" by Campbell, Reece and Mitchell.

    Closing the Openings

    • Cells located near the pores and the osculum have the ability to contract and close these openings, according to "Biology."

    Reproduction

    • To reproduce, some of the amoebocyte cells undergo a change so that they can produce eggs or sperm. The sperm cells are swept out of one sponge and into another by a current of water. The choanocytes trap the sperm cells, change form and transport them to the eggs. Fertilization then takes place. The resulting fertilized cells are called zygotes. They have flagella by which they can swim abroad, settle down on a suitable base and start a new sponge, according to Belleramine University and Earth Life.