Study Guide for Chapter 31

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Biological Sciences
Mary Olaveson

Biology Chapter 31 Animals Origins and the Evolution of Body Plans Convincing evidence that all organisms considered to be animals share a common ancestor comes form there many shared derived molecular and morphological traits, much of which we have described in earlier chapters: -Many gene sequences such as the ribosomal RNA genes support the monophyly of animals. -Animals display similarities in the organization and function of their Hox genes -Animals have unique types of junctions between their cells (tight junctions, desmosomes, and gap junctions) -Animals have common extracellular matrix molecules, including collagen and proteoglycans -Clues to the evolutionary relationships among animal groups thus must be sought in derives traits that are found in some groups such as -Characteristics in fossils -Patterns in embryonic development -Morphology -Physiology of living animals, - The structure of animal molecules and in the genomes of animals (mitochondrial and RNA genes) Cleavage- the first few cell divisions of a zygote Cleavage patterns- different ways of cell division among different animals? -patterns are influenced by the configuration of the yolk the nutritive material that nourishes the growing embryo. Diploblastic animals- have only two of these cell layers: ectoderm- outer layer endoderm- inner layer Triploblastic animals- have three cell layers ectoderm endoderm mesoderm-lies between the ectoderm and endoderm Gastulation- a process where a hollow ball one cell thick indents to form a cup shaped Structure Blastopore- the opening of the cavity formed by this indentation -The pattern of development after formation of the blastopore has been used to provide the triploblastic animals into two major groups: 1) Protostomes- mouth first, the mouth arises from the blastopore; the anus forms later - Appears to be the derived condition 2) Deuterstomes-mouth second, the blastopore becomes the anus; the mouth forms later. - Appears to be the ancestral condition Body plan - the general structure of an animal, the arrangement of its organ systems, and the integrated functioning of its parts
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