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Biology (Sci)
BIOL 111

Bio 111 Alanna Houston October 23, 2007 - Look at animal phylogeny - Sponges do not have tissues - Multicellularity has evolved more than once in the evolutionary history of life. - - Bilateral symmetry evolved at D (protostomes and deuterostomes) - The first triploblasts (3 layers of cells) also evolved at D - The flatworms are at F (Lophotrochozoans) - Protostomes and Deuterostomes split in the Cambrian period - Animals have cleavage (huge ball of cells from one cell) in embryonic development: Bio 111 Alanna Houston - - Protostomes: blastopore becomes mouth and second opening becomes anus (worms) - Deuterostomes: blastopore becomes anus and second opening becomes mouth (humans) - Digestive tract evolved at D although arrow worms and lophotrochozoans lost it through evolution and only has a digestive cavity - Advantages of digestive tract: o Specialization of gut regions o Sequential food processing o Continuous operation - One difference between the three groups of worms is body cavity (coel = cavity) Acoelomate: - no coelom (no body cavity) - solid except for gut space - flatworms, (cnidarians – diploblasts) Pseudocoelomate: - false coelom - mesoderm lines the outside of the coelom - nematodes Coelomate: - mesoderm lines entire cavity as a ‘peritoneum’ - annelids - A coelom provides hydrostatic support, locomotion, storage, space for organ development, isolation of digestive tract PROTOSTOMES Lophtrochozoans: - move using cilia - Annelids: o 15000 species o Segmented worms Bio 111 Alanna Houston o Terrestrial and aquatic o Coelomates o 0.5mm – 3.0 m o Segmentation o Segmentation is advantageous  Multiple copies of organs, structures  Efficient nervous control: ganglion in each segment therefore faster responses  Modification of segments  Better control of movement  Increases body size by unit repetition o Look at pictures of annelid segments o Locomotion with segments  Each segment has longitudinal and circular muscles and coelomic space  Coelomic fluid trapped in each segment and anterior end elongates  Longitudinal muscles contract and the posterior end brought forward o Annelid Systems  Respiratory system: skin (epidermis)  Nervous system: anterior brain, ganglia, ventral nerve cord  Circulatory system: closed, dorsal and ventral blood vessels, aortic arches = hearts o Advantages of circulatory system:  Improved exchange between deeper tissues and surface (O2 and CO2) and gut and muscles (nutrient delivery)  Permits development of a thicker body (free of diffusion limit) o E
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