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active transport
Pumping of a specific solute across a cell membrane against its concentration gradient, through the interior of a transport protein. Requires energy input, as from ATP.
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adhesion proteins
Of multicelled species, a plasma membrane protein that helps cells stick together in tissues and to extracellular matrixes such as basement membrane.
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biofilms
Large microbial populations that anchored themselves to epithelium, rocks, or other surfaces by their own secretions.
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bulk flow
The mass movement of one or more substances in the same direction, most often in response to pressure.
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calcium pump
Active transport protein; pumps calcium ions across a cell membrane against their concentration gradient.
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communication proteins
A membrane protein that helps form an open channel between the cytoplasm of adjoining cells.
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concentration gradient
Difference in the number of molecules or ions of any one substance between two adjoining regions.
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diffusion
Net movement of like ions or molecules from a region where they are most concentrated to an adjoining region where they are less concentrated; they move down their concentration gradient.
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electric gradient
A difference in electric charge between adjoining regions.
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endocytosis
Cell uptake of substances by forming vesicles from patches of plasma membrane. Three modes are receptor-mediated endocytosis, phagocytosis, and the bulk transport of extracellular fluid.
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exocytosis
Fusion of a cytoplasmic vesicle with the plasma membrane; as it becomes part of the membrane, its contents are released to extracellular fluid.
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fluid mosaic model
A cell membrane has a mixed composition (mosaic) of lipids and proteins, the interactions and motions of which impart fluidity to it.
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hydrostatic pressure
Pressure exerted by a volume of fluid against a cell wall, membrane, or some other structure that contains it; also called turgor pressure.
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hypertonic solution
Of two fluids, the one with the higher solute concentration.
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hypotonic solution
Of two fluids, the one with the lower solute concentration.
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isotonic solution
Any fluid having the same solute concentration as another fluid to which it is being compared.
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lipid bilayer
Structural basis of all cell membranes; mainly phospholipids arranged tail-to-tail in two layers, with hydrophilic heads of one dissolved in cytoplasmic fluid and heads of the other in extracellular fluid.
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osmosis
Diffusion of water across a selectively permeable membrane from a region where the water concentration is higher to a region where it is lower.
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osmotic pressure
The amount of pressure which, when applied to a hypertonic fluid, will stop osmosis from occurring across a semipermeable membrane.
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passive transport
Diffusion of a solute across a cell membrane, through the interior of a transport protein.
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phagocytosis
[Gk. phagein, to eat] �Cell eating,� a common endocytic pathway by which various cells engulf food bits, microbes, and cellular debris.
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phospholipid
A lipid with a phosphate group in its hydrophilic head. The main constituent of cell membranes.
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pressure gradient
Difference in pressure between two adjoining regions.
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recognition proteins
One of a class of glycoproteins or glycolipids that project above the plasma membrane and that identify a cell as nonself (foreign) or self (belonging to one�s own body tissue).
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selective permeability
Built-in capacity of a cell membrane to prevent or allow specific substances from crossing it at certain times, in certain amounts.
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sodium-potassium pump
Cotransporter that, when energized, actively transports sodium out of a cell and helps potassium passively diffuse into it at the same time.
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tonicity
Relative solute concentrations of two fluids.
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transport proteins
Membrane protein that passively or actively assists specific ions or molecules into or out of a cell. The solutes move through the protein�s interior.
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