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Chapter 3

BIOL 2030 Chapter 3.docx

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York University
BIOL 2030
German Reyes

Chapter 3: Animal Architecture The Hierarchical Organization of Animal Complexity  Eukaryotic cell is the basic building block of animals  There are 5 major levels of organization within the eukaryotes 1. Protoplasmic Level a. Characterizes unicellular organisms b. All life functions confined within the cell i. Organelles perform specialized functions c. Cells vary in terms of their subcellular structures 2. Cellular Level a. Either colonial or multicellular i. Colonial 1. Aggregation of undifferentiated cells 2. Unspecialized 3. All are able to reproduce ii. Multicellular 1. Aggregation of functionally differentiated cells 2. Specialized 3. Reproduction is limited to certain cells only 4. Its evolution evolved independently in as many as 25 lineages of which is a lineage, called Opisthokonta, which led to the animals b. The aggregated cells communicate with each other i. May secrete extracellular matrix (ECM) to which cells adhere c. Examples: protozoan colonial forms and some place the sponges (phylum: porifera) at this level 3. Cell-Tissue Level a. Similar cells aggregate into definite patterns or layers b. Tissue = a group of similar cells organized to perform a common function c. Has 3 distinct types of junctions between cells: i. Adherens ii. Separate iii. Gap junctions d. Examples: Cnidarians such as jellyfish; some place sponges at this level i. Excellent example of tissue is the Cnidarian nerve net formed from nerve cells and function in coordination 4. Tissue-Organ Level a. Tissues assemble into organs b. More specialized function than tissues c. Usually one type of tissue carries the burden of an organ’s chief function i. Parenchyma = chief functional cells of an organ 1. E.g. muscle tissue in heart ii. Stroma = supportive tissues of an organ 1. E.g. epithelial, connective, and nervous tissues in heart d. Example: flatworms (platyhelminthes) i. Flatworms have well-defined organs such as eyespots, a digestive tract, and reproductive organs 5. Organ-System Level a. Organs operate together to perform some function b. Systems are associated with basic body functions c. 11 Systems in metazoans: i. skeletal vii. excretory ii. muscular viii. nervous iii. integumentary ix. endocrine iv. digestive x. immune v. respiratory xi. reproductive vi. circulatory d. Examples: most animals demonstrate this level of organization i. Some examples are: frog (phylum: chordate), crab (phylum: arthropod), and earthworm (phylum: annelid) Animal Body Plans  Animal Symmetry Symmetry = balanced proportions / correspondence in size & shape of parts on opposite sides of a median plane o Asymmetrical Bodies  Not balanced  No plane through which they can be divided into identical halves o Spherical symmetry  Any plane passing through the center divides the body into equivalent/mirrored halves  Best suited for floating or rolling organisms  Example: some protozoans; rare in animals o Radial symmetry  Forms that can be divided into similar halves by more than 2 planes passing through the longitudinal axis  Best suited for: sessile, free-floating, or weakly swimming organisms  In sessile forms, the aboral (region opposite the mouth) surface is used for attachment  Common in: Tubular-shaped, vase-shaped, or bowl-shaped animals which in one end of the longitudinal axis is usually the oral surface (mouth)  Example: hydras & jelly fishes (phylum: Cnidaria), sea urchins (phylum: Echinodermata), and some sponges (phylum: Porifera)  Radial symmetry: Biradial symmetry  Some part that’s single or paired can be divided into 1 or 2 planes passing through the longitudinal axis to produce mirrored halves  Example: sea walnuts and comb jellies (phylum: Ctenophora) o They’re roughly globular in form but have a pair of tentacles  Example: echinoderms are primarily bilateral (during larval stages) and secondarily radial (during adult stage)  Radiata: animals that are primarily radially symmetrical  Example: phyla Cnidaria and Ctenophora o Bilateral symmetry  Forms that can be divided along sagittal plane into 2 mirrored portions  i.e. left & right halves  major innovation because allows organisms to be better fitted for directional movement  strongly related to cephalization  cephalization = differentiation of a head end  advantageous on animals moving in its environment head first o grants ability to sense and respond to environment  accompanied by differentiation along the anteroposterior axis o i.e. polarity o important during development where the poles produce gradient of chemical signals  regions of body develop differently  Bilateria: animals that are bilaterally symmetrical  Development of Animal Body Plans o Zygote  Formed post-fertilization of egg  Single large cell o Blastomere  Formed post-cleavage of zygote  Cleavage = orderly sequence of cell division o Adult structures do not form until well after cleavage o Occurs in different ways:  Poriferans & Cnidarians lack distinct cleavage pattern  Bilateria exhibit either radial or spiral cleavage o Radial Cleavage  Produces tiers/layers of cells on top of each other in an early embryo  Occurs with regulative development  Each blastomere that’s separated from the others can adjust its development into complete and well-proportioned embryo o Spiral Cleavage  By the 8 cell stage, cleavage produces 2 quartets of cells that furrows between cells  Tend to pack their cells tightly together  Most have a form of mosaic development  Organ-forming determinants in egg cytoplasm become strictly localized in egg  Leads to separated blastomere continuing to develop for a time as if it’s still part of the whole finally forming into defective, partial embryo  At the 29 cell stage, a blastomere called the 4d cell, is formed that will give rise to all mesoderm of the embryo  Large # of smaller-than-zygote cells o Blastula  Many blastomeres surrounding blastocoel  Blastocoel =
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