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Poorly Written Answer is not written properly. Factually Incorrect Facts stated in the Answer are incorrect. Water entering the spongocoel is extruded via a large, common opening called the osculum. However, sponges exhibit a range of diversity in body forms, including variations in the size of the spongocoel, the number of osculi, and where the cells that filter food from the water are located. The specialized cell types in sponges b each perform a distinct function.
While sponges excluding the Hexactinellids do not exhibit tissue-layer organization, they do have different cell types that perform distinct functions. Pinacocytes, which are epithelial-like cells, form the outermost layer of sponges, enclosing a jelly-like substance called mesohyl. Mesohyl is an extracellular matrix consisting of a collagen -like gel with suspended cells that perform various functions. The gel-like consistency of mesohyl acts as an endoskeleton, maintaining the tubular morphology of sponges.
In addition to the osculum, sponges have multiple pores called ostia on their bodies that allow water to enter the sponge. In some sponges, ostia are formed by porocytes: single, tube-shaped cells that act as valves to regulate the flow of water into the spongocoel. In other sponges, ostia are formed by folds in the body wall of the sponge. Whereas pinacocytes line the outside of the sponge, choanocytes tend to line certain inner portions of the sponge body that surround the mesohyl.
The structure of a choanocyte is critical to its function, which is to generate a water current through the sponge and to trap and ingest food particles by phagocytosis. Note that there is a similarity in appearance between the sponge choanocyte and choanoflagellates Protista. This similarity suggests that sponges and choanoflagellates are closely related and probably share a recent, common ancestry. The cell body is embedded in mesohyl. The cumulative effect of the flagella from all choanocytes aids the movement of water through the sponge: drawing water into the sponge through the numerous ostia, into the spaces lined by choanocytes, and eventually out through the osculum or osculi.
Meanwhile, food particles, including waterborne bacteria and algae, are trapped by the sieve-like collar of the choanocytes, slide down into the body of the cell, are ingested by phagocytosis, and become encased in a food vacuole. Finally, choanocytes will differentiate into sperm for sexual reproduction; they will become dislodged from the mesohyl, leaving the sponge with expelled water through the osculum.
The second crucial cells in sponges are called amoebocytes or archaeocytes , named for the fact that they move throughout the mesohyl in an amoeba-like fashion. Amoebocytes have a variety of functions: delivering nutrients from choanocytes to other cells within the sponge; giving rise to eggs for sexual reproduction which remain in the mesohyl ; delivering phagocytized sperm from choanocytes to eggs; and differentiating into more-specific cell types.
Some of these more-specific cell types include collencytes and lophocytes, which produce the collagen-like protein to maintain the mesohyl; sclerocytes, which produce spicules in some sponges; and spongocytes, which produce the protein spongin in the majority of sponges. These cells produce collagen to maintain the consistency of the mesohyl.
Sponges are sessile, feed by phagocytosis, and reproduce sexually and asexually; all major functions are regulated by water flow diffusion. Sponges, despite being simple organisms, regulate their different physiological processes through a variety of mechanisms. These mechanisms regulate metabolism, reproduction, and locomotion. Sponges lack complex digestive, respiratory, circulatory, reproductive, and nervous systems. Their food is trapped when water passes through the ostia and out through the osculum.
Bacteria smaller than 0. Particles that are larger than the ostia may be phagocytized by pinacocytes. In some sponges, amoebocytes transport food from cells that have ingested food particles to those that do not. For this type of digestion, in which food particles are digested within individual cells, the sponge draws water through diffusion.
The limit of this type of digestion is that food particles must be smaller than individual cells. 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 openings.
All cell types within the sponge obtain oxygen from water through diffusion. Likewise, carbon dioxide is released into seawater by diffusion. In addition, nitrogenous waste produced as a by-product of protein metabolism is excreted via diffusion by individual cells into the water as it passes through the sponge. Water flow in a sponge : In a sponge, water enters through the body pores and exits in the direction of the osculum direction of blue arrow.
This diffusion of water through the body supports major functions in the sponge. Sponges reproduce by sexual, as well as, asexual methods. The typical means of asexual reproduction is either fragmentation where a piece of the sponge breaks off, settles on a new substrate, and develops into a new individual or budding a genetically-identical outgrowth from the parent eventually detaches or remains attached to form a colony.
An atypical type of asexual reproduction is found only in freshwater sponges, occurring through the formation of gemmules. Gemmules are environmentally-resistant structures produced by adult sponges wherein the typical sponge morphology is inverted.
In gemmules, an inner layer of amoebocytes is surrounded by a layer of collagen spongin that may be reinforced by spicules. The collagen that is normally found in the mesohyl becomes the outer protective layer. In freshwater sponges, gemmules may survive hostile environmental conditions such as changes in temperature. They serve to recolonize the habitat once environmental conditions stabilize. Gemmules are capable of attaching to a substratum and generating a new sponge. Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism.
Sexual reproduction in sponges occurs when gametes are generated. Sponges are monoecious hermaphroditic , which means that one individual can produce both gametes eggs and sperm simultaneously.
In some sponges, production of gametes may occur throughout the year, whereas other sponges may show sexual cycles depending upon water temperature. Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later.
Oocytes arise by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa result from the differentiation of choanocytes and are ejected via the osculum.
Ejection of spermatozoa may be a timed and coordinated event, as seen in certain species. Spermatozoa carried along by water currents can fertilize the oocytes borne in the mesohyl of other sponges.
Early larval development occurs within the sponge; free-swimming larvae are then released via the osculum. Sponges are generally sessile as adults and spend their lives attached to a fixed substratum. They do not show movement over large distances as do free-swimming marine invertebrates. However, sponge cells are capable of creeping along substrata via organizational plasticity.
Under experimental conditions, researchers have shown that sponge cells spread on a physical support demonstrate a leading edge for directed movement. It has been speculated that this localized creeping movement may help sponges adjust to microenvironments near the point of attachment.
It must be noted, however, that this pattern of movement has been documented in laboratories, but it remains to be observed in natural sponge habitats.
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