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CH07 Membrane Structure and Function - Vocab
Vocabulary from Chapter 7 of Campbell Biology (9th ed.)
37
Biology
Undergraduate 2
02/28/2011

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Term
active transport
Definition
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.
Term
amphipathic
Definition
Having both a hydrophilic region and a hydrophobic region.
Term
aquaporins
Definition
A channel protein in the plasma membrane of a plant, animal or microorganism cell that specifically facilitates osmosis, the diffusion of free water across the membrane.
Term
concentration gradient
Definition
A region along which the density of a chemical substance increases or decreases.
Term
cotransport
Definition
The coupling of the “downhill” diffusion of one substance with the “uphill” transport of another against its own concentration gradient.
Term
diffusion
Definition
The spontaneous movement of a substance down its concentration or electrochemical gradient, from a region where it is more concentrated to a region where it is less concentrated.
Term
electrochemical gradient
Definition
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).
Term
electrogenic pump
Definition
An active transport protein that generates voltage across a membrane while pumping ions.
Term
endocytosis
Definition
Cellular uptake of biological molecules and particulate matter via formation of vesicles from the plasma membrane.
Term
exocytosis
Definition
The cellular secretion of biological molecules by the fusion of vesicles containing them with the plasma membrane.
Term
facilitated diffusion
Definition
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.
Term
flaccid
Definition
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.)
Term
fluid mosaic model
Definition
The currently accepted model of cell membrane structure, which envisions the membrane as mosaic of protein molecules drifting laterally in a fluid bilayer of phospholipids.
Term
gated channels
Definition
A transmembrane protein channel that opens or closes in response to a particular stimulus.
Term
glycolipids
Definition
A lipid with one or more covalently attached carbohydrates.
Term
glycoproteins
Definition
A protein with one or more covalently attached carbohydrates.
Term
hypertonic
Definition
Referring to a solution that, when surrounding a cell, will cause the cell to lose water.
Term
hypotonic
Definition
Referring to a solution that, when surrounding a cell, will cause the cell to take up water.
Term
integral proteins
Definition
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).
Term
ion channels
Definition
A transmembrane protein channel that allows a specific ion to diffuse across the membrane down its concentration or electrochemical gradient.
Term
isotonic
Definition
Referring to a solution that, when surrounding a cell, causes no net movement of water into or out of the cell.
Term
ligands
Definition
A molecule that binds specifically to another molecule, usually another one.
Term
membrane potential
Definition
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.
Term
osmoregulation
Definition
Regulation of solute concentrations and water balance by a cell or organism.
Term
osmosis
Definition
The diffusion of free water across a selectively permeable membrane.
Term
passive transport
Definition
The diffusion of a substance across a biological membrane with no expenditure of energy.
Term
peripheral proteins
Definition
A protein loosely bound to the surface of a membrane or to part of an integral protein and not embedded in the lipid bilayer.
Term
phagocytosis
Definition
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).
Term
pinocytosis
Definition
A type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes.
Term
plasmolysis
Definition
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.
Term
proton pump
Definition
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.
Term
receptor-mediated endocytosis
Definition
The movement of specific molecules into a cell by the inward budding of vesicles containing proteins with receptor sites specific to the molecules being taken in; enables a cell to acquire bulk quantities of specific substances.
Term
selective permeability
Definition
A property of biological membranes that allows them to regulate the passage of substances across them.
Term
sodium-potassium pump
Definition
A transport protein in the plasma membrane of animal cells that actively transports sodium out of the cell and potassium into the cell.
Term
tonicity
Definition
The ability of a solution surrounding a cell to cause that cell to gain or lose water.
Term
transport proteins
Definition
A transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane.
Term
turgid
Definition
Swollen or distended, as in plant cells. (A walled cell becomes turgid if it was a lower water potential than its surroundings, resulting in the entry of water.)
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