| Term | Definition |
|---|
| diffusion | the spontaneous movement of a substance down its concentration gradient, from a region where it is more concentrated to a region where it is less concentrated |
| concentration gradient | a region along which the density of a chemical substance increases or decreases |
| passive transport | the diffusion of a substance across a biological membrane with no expenditure of energy |
| osmosis | the diffusion of water across a selectively permeable membrane |
| tonicity | the ability of a solution surround a cell to cause that cell to gain or loose water |
| isotonic | referring to a solution that, when surrounding a cell, has no effect on the passage of water into or out of a cell |
| hypertonic | reffering to a solution that, when surrounding a cell, will cause the cell to lose water |
| hypotonic | reffering to a solution, that when surrounding a cell, will cause the cell to take up water |
| osmoregulation | regulation of solute concentrations and water balance by a cell or organism |
| turgid | swollen or distended, as in plants ( a walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water) |
| flaccid | limp. lacking in stiffness, as in plant cell in surroundings where there is no tendency for water to enter the cells |
| 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 |
| facilitated diffusion | the spontaneous passage of molecules or ions across a biological membrane with the assistance of specific transmembrane transport proteins |
| ion channel | a transmembrane protein channel that allows a specific ion to flow across the membrane down its concentration gradient |
| gated channel | a transmembrane protein channel that opens or closes in response to a particular stimulus |
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