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| 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. |
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| A molecule that has both a hydrophilic region and a hydrophobic region. |
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| A transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis). |
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| 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. |
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| The coupling of the downhilldiffusion of one substance to the uphilltransport of another against its own concentration gradient. |
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| The spontaneous tendency of a substance to move down its concentration gradient from a more concentrated to a less concentrated area. |
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| 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. |
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| An ion transport protein that generates voltage across a membrane. |
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| 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. |
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| The cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane. |
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| The spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients. |
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| Limp. A walled cell is flaccid in surroundings where there is no tendency for water to enter. |
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| 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. |
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| A protein channel in a cell membrane that opens or closes in response to a particular stimulus. |
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| In comparing two solutions, referring to the one with a greater solute concentration. |
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| In comparing two solutions, referring to the one with a lower solute concentration. |
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| Typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane. |
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| Having the same solute concentration as another solution. |
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| A molecule that binds specifically to a receptor site of another molecule. |
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| The charge difference between a cell’s cytoplasm and the extracellular fluid, due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances. |
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| The regulation of solute and water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, and terrestrial environments. |
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Definition
| The diffusion of water across a selectively permeable membrane. |
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Definition
| The diffusion of a substance across a biological membrane. |
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| A protein appendage loosely bound to the surface of a membrane and not embedded in the lipid bilayer. |
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| A type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells. |
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| A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes. |
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| 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. |
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| An active transport mechanism in cell membranes that uses ATP to force hydrogen ions out of a cell, generating a membrane potential in the process. |
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Term
| receptor-mediated endocytosis |
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Definition
| 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. |
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| A property of biological membranes that allows some substances to cross more easily than others. |
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| 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. |
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Definition
| A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane. |
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| Very firm. A walled cell become turgid if it has a greater solute concentration than its surroundings, resulting in entry of water. |
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