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cell theory
All organisms are composed of one or more cells, within which the processes of life occur
Cells are the smallest living things. Nothing smaller than a cell is considered alive
Cells arise only by division of a previously existing cell. Although life likely evolved spontaneously in the environment of the early earth, biologists have concluded that no additional cells are originating spontaneously at present. Rather, life on earth represents a continuous line of descent from those early cells
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surface-to-volume ratio
as cell size increases, volume grows much more rapidly than surface area
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plasma membrane
lipid bilayer membrane encasing cells
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phospholipids
- polar head w/ two non-polar tails
- form the basic structure of the plasma membrane
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membrane proteins
float within the lipid bilayer
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cell surface proteins
act as markers to identify particular types of cells, or as beacons to bind specific hormones or proteins to the cell
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transmembrane proteins
provide pasageways for ions and polar molecules to pass into and out of the cell
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prokaryotes
- simplest cellular organisms; small, single-celled, most have cell wall and plasma membrane
- no organelles
- no nucleus
- uniform cytoplasm (no subdivision)
examples: bacteria and archaea
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flagellum
long, threadlike structures, made of protein fibers that project from the surface of a cell
used for feeding and locomotion
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organelle
specialized structure within which particular cell processes occur
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