AGRC1020 Lecture Notes - Lecture 9: Ediacaran, Ediacara Hills, Tight Junction
6 Aug 2018
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Biologists have identified 1. 3 million living species of animals. Estimates of the total number of animal species run far higher, from 10 to million to as many as 100 to 200 million. Eukaryotes with tissues that develop from embryonic layer. There are exceptions to nearly every criterion for distinguishing an anima other life forms. However, five criteria, taken together, comprise a reasonable definition. Animals take in preformed organic molecules through ingestion other organisms or organic material that is decomposing. Animal cells lack cell walls that provide structural support for plants a fungi. The multicellular bodies of animals are held together by extrace structural proteins, especially collagen. Animals have other unique types of intercellular junctions, inclu tight junctions, desmosomes, and gap junctions, which hold tissu together. These junctions are also composed of structural proteins. Animals have two unique types of cells: nerve cells for impulse cond and muscle cells for movement.
