Chapter 7

Front 1

active transport

Back 1

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.

Front 2

amphipathic

Back 2

Having both a hydrophilic region and a hydrophobic region

Front 3

aquaporin

Back 3

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

Front 4

concentration gradient

Back 4

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

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 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.

Front 7

electrochemical gradient

Back 7

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).

Front 8

electrogenic pump

Back 8

An active transport protein that generates voltage across a membrane while pumping ions.

Front 9

endocytosis

Back 9

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

Front 10

exocytosis

Back 10

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

Front 11

facilitated diffusion

Back 11

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 expenditur

Front 12

flaccid

Back 12

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.)

Front 13

fluid mosaic model

Back 13

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

Front 14

gated channel

Back 14

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

Front 15

glycolipid

Back 15

A lipid with one or more covalently attached carbohydrates.

Front 16

glycoprotein

Back 16

A protein with one or more covalently attached carbohydrates

Front 17

hypertonic

Back 17

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

Front 18

hyotonic

Back 18

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

Front 19

integral protein

Back 19

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).

Front 20

ion channel

Back 20

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

Front 21

isotonic

Back 21

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

Front 22

ligand

Back 22

A molecule that binds specifically to another molecule, usually a larger one.

Front 23

membrane potential

Back 23

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.

Front 24

osmoregulation

Back 24

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

Front 25

osmosis

Back 25

The diffusion of free water across a selectively permeable membrane

Front 26

peripheral protein

Back 26

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

Front 27

phagocytosis

Back 27

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).

Front 28

pinocytosis

Back 28

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

Front 29

plasmolsis

Back 29

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.

Front 30

proton pump

Back 30

An active transport protein in a cell membrane that uses ATP to transport hydrogen ions out of a cell against their concentration gradient, generating a membrane potential in the process.

Front 31

receptor-mediated

Back 31

The movement of specific molecules into a cell by the infolding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.

Front 32

selective permeability

Back 32

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

Front 33

sodium-potassium pump

Back 33

A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.

Front 34

tonicity

Back 34

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

Front 35

transport protein

Back 35

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

Front 36

turgid

Back 36

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.)