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BSsqans-lect09 pori

BSsqans-lect09 pori - choanocytes whose flagellar movements...

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BIS 1B (Winter 2008) Study question answers: Porifera Lecture 9 1. Describe the skeletal system of a sponge. The skeletal system is produced by cells in the mesohyl (gel matrix), and has both organic and inorganic components. The organic component is made up of strong, pliable fibers of the protein collagen. In many sponges, collagen fibers occur in a modified form called spongin. (Spongin gives commercial sponges their water- absorbing properties.) The inorganic component is made up of rigid spicules, containing either silica (siliceous spicules) or calcium carbonate (calcareous spicules). 2. How do sponges generate a flow of water through their bodies? The water current (or aquiferous) system of a sponge is a series of tubes and chambers that brings water through the sponge, and close to the cells responsible for feeding, gas exchange, and excretion. Although the architecture of this plumbing system is quite variable, the water flow is generated by flagellated collar cells, the
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Unformatted text preview: choanocytes, whose flagellar movements cause water to enter through the ostia and escape from the osculum. 3. How do sponges feed? Sponges are filter (or suspension) feeders. Choanocytes create a current of water. The flagellum of each choanocyte is surrounded by a collar-like sieve (composed of microvilli, cross-connecting microfibrils, and mucus) that functions as a filter. Water passes through this filter and small food particles (e.g., plankton) are trapped and ingested by the choanocyte and passed on to archaeocytes (ameboid cells) in the mesohyl for intracellular digestion. 4. What animal-like features are lacking in sponges? Sponges lack true tissues, a nervous system, muscle cells, differentiated head, etc. There is also no gastrulation and consequently no production of germ layers (ectoderm and entoderm). Nor is there an elaborate gas exchange and excretion system, since wastes and gases move by simple diffusion. 1...
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