Chapter 32

Chapter 32 - Chapter 32: An Introduction to Animals...

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Chapter 32: An Introduction to Animals Animals: a monophyletic group of eukaryotes that can be recognized by three traits o Multicellular o Ingest their food o Move under their own power at some point in their life cycle Heterotrophs: obtaining carbon compounds they need from other organisms Primary producers: photosynthetic protists and bacteria that form the base of the food chain in most marine environments Consumers: occupy upper levels of food chains in both marine and terrestrial regions; eat producers and other organisms *The cells of animals lack walls but have an extensive extracellular matrix, which includes proteins specialized for cell-cell adhesion and communication. Animals are the only lineage on the tree of life with species that have muscle tissue and nervous tissue. *Although many animals reproduce both sexually and asexually, no animals undergo alternation of generations. During an animal’s life cycle, adults of most species are diploid; the only haploid cells are gametes produced during sexual reproduction. *Four basic elements of an animal’s body plan: o Number of tissue layers found in embryos o Type of body symmetry and degree of cephalization (informally, this means the formation of a head region) o The presence or absence of a fluid-filled body cavity o The way in which the earliest events in the development of an embryo proceed Tissues: tightly integrated structural and functional units Epithelium: a layer of tightly joined cells that covers the surface The number of tissue layers that exist in an embryo is a key trait: o Diploblast: two types of tissue layers (endoderm and ectoderm) Same pattern as below holds true, except (1) muscle is simpler in organization and is derived from ectoderm, and (2) reproductive tissues are derived from endoderm Cnidarians and ctenophorans o Triploblast: three types of tissue layers (endoderm, ectoderm, and mesoderm) Ectoderm: forms skin and nervous system Endoderm: forms lining of the digestive tract Mesoderm: circulatory system, muscle, and internal structures such as bone and most organs Symmetry and cephalization o Asymmetry: having no planes of symmetry Ex: sponges o Radial: have at least two planes of symmetry Ex: jellyfish Most either float in water or live attached to a substrate o Bilateral: have one plane of symmetry and tend to have a long, narrow body Ex: humans o Cephalization: the evolution of a head, or anterior region where structures for feeding, sensing the environment, and processing information are concentrated o All triploblastic organisms, except echinoderms, have bilateral symmetry. Echinoderms are radially symmetric, but their larvae are bilaterally symmetric.
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o *To explain the pervasiveness of bilateral symmetry, biologists point out that locating and capturing food is particularly efficient when movement is directed by a distinctive head region and powered by a long posterior region. In combination with the origin of mesoderm,
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This note was uploaded on 04/15/2008 for the course LS 1 taught by Professor Thomas during the Winter '05 term at UCLA.

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Chapter 32 - Chapter 32: An Introduction to Animals...

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