front 1 active transport | back 1 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. |
front 2 amphipathic molecule | back 2 A molecule that has both a hydrophilic region and a hydrophobic region. |
front 3 aquaporin | back 3 A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis). |
front 4 concentration gradient | back 4 An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes. When a gradient exists, the ions or other chemical substances involved tend to move from where they are more concentrated to where they are less concentrated. |
front 5 cotransport | back 5 The coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient. |
front 6 diffusion | back 6 The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area. |
front 7 electrochemical gradient | back 7 The diffusion gradient of an ion, representing a type of potential energy that accounts for both the concentration difference of the ion across a membrane and its tendency to move relative to the membrane potential. |
front 8 electrogenic pump | back 8 An ion transport protein generating voltage across the membrane. |
front 9 endocytosis | back 9 The cellular uptake of macromolecules and particulate substances by localized regions of the plasma membrane that surround the substance and pinch off to form an intracellular vesicle. |
front 10 exocytosis | back 10 The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane. |
front 11 facilitated diffusion | back 11 The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients. |
front 12 flaccid | back 12 Limp. Walled cells are flaccid in isotonic surroundings, where there is no tendency for water to enter. |
front 13 fluid mosaic model | back 13 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. |
front 14 gated channel | back 14 A protein channel in a cell membrane that opens or closes in response to a particular stimulus. |
front 15 glycoprotein | back 15 A protein covalently attached to a carbohydrate. |
front 16 hypertonic | back 16 In comparing two solutions, referring to the one with a greater solute concentration. |
front 17 hypotonic solution | back 17 In comparing two solutions, the one with a lower solute concentration. |
front 18 integral protein | back 18 Typically transmembrane proteins with hydrophobic regions that completely span the hydrophobic interior of the membrane. |
front 19 isotonic | back 19 Having the same solute concentration as another solution. |
front 20 ligand | back 20 A molecule that binds specifically to a receptor site of another molecule. |
front 21 membrane potential | back 21 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. |
front 22 osmoregulation | back 22 The control of water balance in organisms living in hypertonic, hypotonic, or terrestrial environments. |
front 23 osmosis | back 23 The diffusion of water across a selectively permeable membrane. |
front 24 passive transport | back 24 The diffusion of a substance across a biological membrane. |
front 25 peripheral protein | back 25 Protein appendages loosely bound to the surface of the membrane and not embedded in the lipid bilayer. |
front 26 pinocytosis | back 26 A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes. |
front 27 plasmolysis | back 27 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. |
front 28 plasmolyze | back 28 The shrinkage of a cell due to water loss. |
front 29 proton pump | back 29 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. |
front 30 receptor-mediated endocytosis | back 30 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. |
front 31 selective permeability | back 31 A property of biological membranes that allows some substances to cross more easily than others. |
front 32 sodium-potassium pump | back 32 A special transport protein in the plasma membrane of animal cells that transports sodium out of the cell and potassium into the cell against their concentration gradients. |
front 33 transport protein | back 33 A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane. |
front 34 turgid | back 34 Firm. Walled cells become turgid as a result of the entry of water from a hypotonic environment. |