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Chapter 7 Key Terms

Chapter 7: Membrane Structure and Function

aquaporins A channel protein in the plasma membrane of a plant, animal, or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane.
concentration gradient A region along which the density of a chemical substance increases or decreases.
cotransport The coupling of the “downhill” diffusion of one substance to the “uphill” transport of another against its own concentration gradient.
diffusion The spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated.
electrochemical gradient The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).
electrogenic pump An active transport protein that generates voltage across a membrane while pumping ions.
endocytosis Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.
exocytosis The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
flaccid Limp. Lacking turgor, as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)
glycoprotein A protein with one or more covalently attached carbohydrates.
hypertonic Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
hypotonic Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
ion channel A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.
membrane potential The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.
osmoregulation Regulation of solute concentrations and water balance by a cell or organism.
plasmolysis A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall; occurs when the cell loses water to a hypertonic environment.
selective permeability A property of biological membranes that allows them to regulate the passage of substances across them.
sodium-potassium pump A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
turgid Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)
Created by: taylor.wendell



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