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Chapter 8 Key Terms

TermDefinition
selective permeability A property of biological membranes that allows some substances to cross more easily than others.
amphipathic Has both a hydrophilic region and a hydrophobic region.
fluid mosaic model The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally in a fluid bilayer of phospholipids.
integral proteins Generally transmembrane proteins, with hydrophobic regions that completely span the hydrophobic interior of the membrane.
peripheral proteins Proteins that are not embedded in the lipid bilayer at all; they are loosely bound to the surface of the membrane, often to the exposed parts of integral proteins.
transport proteins Proteins that function to transfer specific ions and polar molecules across the plasma membrane.
diffusion The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area.
concentration gradient The principle that in the absence of other forces, a substance will diffuse from where it is more concentrated to where it is less concentrated.
passive transport Diffusion across a membrane.
hypertonic In comparing two solutions of unequal solute concentration, the solution with a higher concentration of solutes is hypertonic.
hypotonic In comparing two solutions of unequal solute concentration, the solution with a lower concentration of solutes is the hypotonic solution.
isotonic Solutions of equal solute concentration are said to be isotonic.
osmosis The passive transport of water.
osmoregulation The control of water balance.
turgid Firm; walled cells become turgid as a result of the entry of water from a hypotonic environment.
plasmolysis A phenomenon in walled cells in which the cytoplasm shrivels and the plasma membrane pulls away from the cell wall when the cell loses water to a hypertonic environment.
facilitated diffusion The phenomenon of many polar molecules and ions impeded by the lipid bilayer of the membrane diffusing with the help of transport proteins that span the membrane.
gated channels Proteins that function to open or close in response to a given stimulus, which could be electrical or chemical. If chemical, it is a substance other than the one to be transported.
active transport The pumping of solutes against their concentration gradients.
sodium-potassium pump A protein pump that exchanges Na ion for K ion.
membrane potential The voltage across a membrane, which ranges from about -50 to -200 millivolts.
electrochemical gradient The combination of chemical force and electrical force acting on an ion. Chemical force is the ion's concentration gradient, and electrical force is the effect of the membrane potential on the ion's movement.
electrogenic pump A transport protein that generates voltage across a membrane.
proton pump The main electrogenic pump of plants, bacteria, and fungi, which actively transports H+ ions (protons) out of the cell.
cotransport A mechanism by which a membrane protein couples the transport of one solute to another.
exocytosis The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane.
phagocytosis A type of endocytosis involving large, particulate substances.
pinocytosis A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
receptor-mediated endocytosis The movement of specific molecules into a cell by the inward budding of membranous vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.
ligand A molecule that binds specifically to a receptor site of another molecule.
Created by: LordWiitalian
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