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20 Cards in this Set
- Front
- Back
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active transport
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the movement of a substance across a biological membrane against its concentration or electrochemical gradient with the help of energy input and specific transport proteins
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apoplast
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In plants, the nonliving continuum formed by the extracellular pathway provided by the continuous matrix of cell walls.
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aquaporin
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A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis).
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bulk flow
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the movement of water due to a difference in pressure between two locations
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Casparian strip
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A water-impermeable ring of wax around endodermal cells in plants that blocks the passive flow of water and solutes into the stele by way of cell walls.
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chemiosmosis
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An energy-coupling mechanism that uses energy stored in the form of a hydrogen ion gradient across a membrane to drive cellular work, such as the synthesis of ATP. Most ATP synthesis in cells occurs by chemiosmosis.
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circadian rhythm
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A physiological cycle of about 24 hours that is present in all eukaryotic organisms and that persists even in the absence of external cues.
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cotransport
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the coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient
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flaccid
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limp. walled cells are flaccid in isotonic surroundings, where there is no tendency of water to enter
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guttation
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the exudation of water droplets, caused by root pressure in certain plants
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megapascal (MPa)
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A unit of pressure equivalent to 10 atmospheres of pressure
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membrane potential
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the charge difference between the cytoplasm and extracellular fluid in all cells due to the differential distribution of ions. membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances
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passive transport
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the diffusion of a substance across a biological membrane
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pressure potential
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a component of water potential; a measure of the effect of pressure or tension on a substance's ability to absorb or release water
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proton pump
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An active transport mechanism in cell membranes that consumes ATP to force hydrogen ions out of a cell and, in the process, generates a membrane potential.
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solute potential
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"osmotic potential"; always negative; a measure in the change in water potential of a system due to the presence of solute molecules
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turgid
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Firm. Walled cells become turgid as a result of the entry of water from a hypotonic environment.
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symplast
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In plants, the continuum of cytoplasm connected by plasmodesmata between cells.
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tonoplast
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A membrane that encloses the central vacuole in a plant cell, separating the cytosol from the cell sap.
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water potential
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the physical property predicting the direction in which water will flow, goverend by solute concentration and applied pressure
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