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| Membrane Potential | The charge difference between a cell's cytoplasm and the extracellular fluid, due to the differential distribution of ions. It effects the activity of excitable cells and the transmembrane movement of all charged substances |
| Electrochemical Gradient | 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 |
| Electrogenic Pump | An ion transport protein that generates voltage across a membrane |
| Cotransport | The coupling of the downhill diffusion of one substance to the uphill transport of another against its own concentration gradient |
| exocytosis | The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane |
| phagocytosis | A type of endocytosis involving large, particular substances, accomplished by macrophages, neutrophils, and dendritic cells |
| 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 molecule being taken in and enables a cell to acquire bulk quantities of specific substances |
| Selective permeability | A property of biological membranes that allows some substances to cross more easily than others |
| Amphipathic | A molecule that has both a hydrophilic region and hydrophobic region |
| Fluid mosaic model | The currently accepted model of cell membrane structure, which envisions the membrane as mosaic of individual protein molecules drifting laterally in a fluid bilayer of phospholipids |
| Integral proteins | Typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane |
| Peripheral proteins | A protein appendage loosely bound to the surface of a membrane ad not embedded in the lipid bilayer |
| Transport proteins | A transmembrane protein that helps a certain substance or class of closely related substances to cross the 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 | An increase or decrease in the density of a chemical substance in an area. Cells often maintain concentration gradients of ions across their membranes |
| Passive transport | The diffusion of a substance across a biological membrane |
| Hypertonic | In comparing two solutions, referring t the one with a greater solute concentration |
| Hypotonic | In comparing two solutions, referring to the one with a lower solute concentration |
| Isotonic | Having the same solute concentration as another solute |
| Osmosis | The diffusion of water across a selectively permeable membrane |
| Osmoregulation | How organisms regulate solute concentrations and balance the gain and loss of water |
| Turgid | Very firm. A walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water |
| 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 spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients |
| Gated channels | A protein channel in a cell membrane that opens or closes in response to a particular stimulus |
| Active transport | The movement of a substance across a biological membrane against its concentraion or electrochemical gradient with the help of energy input and specific transport proteins |
| Na-K pump | 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 |
