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img046 - Chapter 4 ”Organization of the Cell” 1...

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Unformatted text preview: Chapter 4: ”Organization of the Cell” 1. Describe the cell theory The cell theory holds that (1) cells are the basic living units of organization and function in all organisms and (2) all cells come from other cells. Evidence that all living cells have evolved from a common ancestor is supported by the basic similarities in their structures and in their molecular composition. " 2. Cell organization and homeostasis The organization of cells is important in maintaining homeostasis, an appropriate internal environment. Cells have many organelles, internal structures that carry out specific functions to help maintain homeostasis. Every cell is surrounded by a plasma membrane that separates it from its external environment. The plasma membrane allows the cell to maintain internal conditions that may be very different from those of the outer environment. The plasma membrane also allows the cell to exchange materials with its outer environment. 3. Cell size and homeostasis A critical factor in determining cell size is the ratio of the plasma membrane to the cell’s volume. The plasma membrane must be large enough relative to the cell volume to regulate the passage of materials into and out of the ell. For this reason, most cells are microscopic. Cell size and shape are related to function and are limited by the need to maintain homeostasis. 4. Prokaryotic and Eukaryotic cells, Plant and animal cells Prokaryotic cells are bounded by a plasma membrane but have little or no internal membrane organization. They have a nuclear area rather than a membrane-enclosed nucleus. Prokaryotic cells typically have a cell wall and ribosomes and may have propeller- like flagella. Eukaryotic cells have a membrane—enclosed nucleus, and their cytoplasm contains a variety of organelles; the fluid component of the cytoplasm is the cytosol. Plant cells differ from animal cells in that plant cells have rigid cell walls, plastids, and large vacuoles; cells of most plants lack centrioles. Vacuoles are important in plant growth and development. 5. Functions of the cell membrane Membranes divide the cell into compartments, allowing it to conduct specialized activities within small areas of the cytoplasm, concentrate reactants, and organize metabolic reactions. Small membrane-enclosed sacs, called vesicles, transport materials between compartments. Membranes are important in energy storage and conversion A system of interacting membranes forms the enclo-membrane system. I""II“"IlllllllllllllllllllllllllllllllllllllilllllllllllllllllllllllllllnilIIllllllllmlllmmIlnIInInImIImImmmum:mummmnmmum.m. ...
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