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Unformatted text preview: Biology 05B Spring Quarter 2009 Lab 2 page 1 Animal Diversity I Biological Classification, an Introduction to 2 Animal Phyla, and Animal Development. Contents: Topic Page 1. Biological Classification 1 2. Phylum Porifera the Sponges 4 3. Phylum Cnidaria the Stinging Animals 7 4. Animal Development Echinoderm Embryology 11 1. BIOLOGICAL CLASSIFICATION A. GENERAL INFORMATION : Because the diversity of living organisms is so enormous, the study of biology would be chaotic without a system of classification that is both logical and meaningful. We could group organisms on the basis of color, size, or the places where they live, and this would impose a certain order on this complexity. However, these sorts of groupings would convey little meaningful information because they are not based on any fundamental differences or similarities among organisms. We need a catalogue of living things that is not only useful in reducing the diversity to manageable proportions, but also will enable us to readily determine the general nature of an organism (its anatomical organization, pattern of development, chemical constitution, etc.) once we are aware of its place in the classification scheme. Thus, once you know the classification of an organism you will also know a great deal about its anatomy, development, etc. The classification system used in biology today is based on phylogenetic relationships. It tells us not only what the organisms are like, but also how closely related they are. The basic organizational category is the species, and this is the only taxonomic group which has a biological definition. A species can be thought of as an assemblage of individuals which can interbreed in nature. However, there are certain practical problems when we are dealing with two or more populations which are geographically separated. How do we know if their members can potentially interbreed? Thus, in practice, individuals which are essentially alike in all details of anatomy are considered the same species. Higher grouping is based on a series of natural relationships which reflect the evolutionary history of present-day organisms. In other words, similarity in body structure usually indicates that the organisms concerned have descended from a common ancestor. If this ancestral relationship is a distant one, only general similarities may be preserved; if two species have branched off from a common stock fairly recently, they will often resemble each other more closely. Thus, it is possible to express the degree of relationship between organisms, and their body features as well, by a series of categories, each more general than the preceding one. Closely related species are grouped together into a genus; related genera make up a family; families are combined into orders, which in turn are contained in classes and finally phyla. An example of how humans are classified is as follows: Biology 05B Spring Quarter 2009 Lab 2 page 2 Domain Eukarya...
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- Spring '09