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Keen S11 -1- BIS 2C Study Questions 3 Metazoans 1. The cnidarian life cycle contains polyps, medusae, and a free-swimming larva. Explain which parts of the life cycle are made by asexual reproduction, which are made by sexual reproduction, and which engage in sexual reproduction. The stage that reproduces sexually is the medusa in Hydrozoan and Scyphozoa. The polyp reproduces sexually and asexually in Anthozoa. When a medusa reproduces sexually gametes fuse to make a free-swimming larva. This settles to become the first polyp of a new genotype. The remaining polyps are made asexually. Polyps also make medusa asexually. 2. What feature is shared between fungi and insect exoskeletons? Why would someone say that this feature first evolved in opisthokonts and is ancestral for all metazoans? They both have chitin in them. Fungi and metazoans are both within Opisthokonta, so it is possible that the common ancestor of fungi and metazoans had chitin, making it ancestral for both clades. 3. Biologists develop a new term, dikaryotic or N + N, for fungi. Why did the diplontic life cycle terms haploid (N) and diploid (2N) not suffice in this case? In ascomycete and basidiomycete fungi there are times when the hyphae fuse and haploid nuclei from two different mating types (genotypes) are in contact (shared cytoplasm), but the nuclei do not fuse. In this case the hyphae with both types of nuclei are N+N. It would be wrong to call the hyphae haploid, but since the nuclei have not fused, they are also not diploid. 4. Which of the following organisms belong to the group of cnidarians without a medusa stage in the life cycle? large ocean-going jellies sea anemones corals cubozoans the polyp stage of hydrozoans 5. Bivalves are unusual molluscs because: a) they have a foot b) they have a mantle c) they lack a radula d) they have a closed circulatory system e) they have gills
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Keen S11 -2- 6 . What is the Principle of Continuity and how does a sponge use it to slow water down during food collection and to speed water up as it exits the body? This Principle says that, given an incompressible fluid and a rigid pipe, the inflow velocity times the inflow cross-sectional area = the outflow velocity times the outflow cross-sectional area. If water enters a sponge through a small pore and reaches an area with a larger cross-sectional area, it will slow down—this is where the choanocytes collect food. When water that entered across a cross- sectional area that is the sum of many tiny inputs exits through a pore that has a cross-sectional area much less than the summed cross-sectional area, it (water) speeds up. This is necessary to avoid re-filtering the same water. 7. How does segmentation permit an annelid to anchor its body? The segments that will anchor the body have the longitudinal muscles
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This note was uploaded on 10/23/2011 for the course BIS 101 taught by Professor Simonchan during the Spring '08 term at UC Davis.

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