chapter 7

The movement of a substance across a cell membrane against its concentration or electrochemical gradient, mediated by specific transport proteins and requiring an expenditure of energy.

Having both a hydrophilic region and a hydrophobic region.

A channel protein in a cellular membrane that specifically facilitates osmosis, the diffusion of free water across the membrane.

A region along which the density of a chemical substance increases or decreases.

The random thermal motion of particles of liquids, gases, or solids. In the presence of a concentration or electrochemical gradient, diffusion results in the net movement of a substance from a region where it is more concentrated to a region where it is less concentrated.

The diffusion gradient of an ion, which is affected by both the concentration difference of an ion across a membrane (a chemical force) and the ion's tendency to move relative to the membrane potential (an electrical force).

Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.

The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.

The passage of molecules or ions down their electrochemical gradient across a biological membrane with the assistance of specific transmembrane transport proteins, requiring no energy expenditure.

Limp. Lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell. (A walled cell becomes flaccid if it has a higher water potential than its surroundings, resulting in the loss of water.)

The currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.

A transmembrane protein channel that opens or closes in response to a particular stimulus.

A lipid with one or more covalently attached carbohydrates.

A protein with one or more covalently attached carbohydrates.

Referring to a solution that, when surrounding a cell, will cause the cell to lose water.

Referring to a solution that, when surrounding a cell, will cause the cell to take up water.

A transmembrane protein with hydrophobic regions that extend into and often completely span the hydrophobic interior of the membrane and with hydrophilic regions in contact with the aqueous solution on one or both sides of the membrane (or lining the channel in the case of a channel protein).

A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.

Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.

The difference in electrical charge (voltage) across a cell's plasma membrane due to the differential distribution of ions. Membrane potential affects the activity of excitable cells and the transmembrane movement of all charged substances.

Regulation of solute concentrations and water balance by a cell or organism.

The diffusion of free water across a selectively permeable membrane.

The diffusion of a substance across a biological membrane with no expenditure of energy.

A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.

A type of endocytosis in which large particulate substances or small organisms are taken up by a cell. It is carried out by some protists and by certain immune cells of animals (in mammals, mainly macrophages, neutrophils, and dendritic cells).

A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.

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.

A property of biological membranes that allows them to regulate the passage of substances across them.

The ability of a solution surrounding a cell to cause that cell to gain or lose water.

A type of integral protein that spans the entire membrane.

A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.

Swollen or distended, as in plant cells. (A walled cell becomes turgid if it has a lower water potential than its surroundings, resulting in entry of water.)