Active Transport
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
Amphipathic Molecule
a molecule that has both a hydrophilic region and a hydrophobic region
Aquaporin
a transport protein in the plasma membrane of a plant or animal cell that specifically facilitates the diffusion of water across the membrane (osmosis)
Concentration Gradient
an increase or decrease in he 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 chemica
Cotransport
the coupling of the downhill diffusion of one substance to the uphill transport of another against its own concentration gradient
Diffusion
the spontaneous tendency of a substance to move down its concentration gradient from a more to a less concentrated gradient
Electrochemical Gradient
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 memb
Electrogenic Pump
an ion transport protein that generates voltage across a membrane
Endocytosis
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
Exocytosis
the cellular secretion of macromolecules by the fusion of vesicles with the plasma membrane
Facilitated Diffusion
the spontaneous passage of molecules and ions, bound to specific carrier proteins, across a biological membrane down their concentration gradients
Flaccid
limp; a walled cell is this in surroundings where there is no tendency for water to enter
Fluid Mosaic Model
the currently accepted model of cell membrane structure, which envisions the membrane as a mosaic of individually inserted protein molecules drifting laterally on a fluid bi-layer of phospholipid
Gated Channel
a protein channel in a cell membrane that opens or closes in response to a particular stimulus
Glycolipid
a lipid covalently attached to a carbohydrate
Glycoprotein
a protein covalently attached to a carbohydrate
Hypertonic
in comparing two solutions, referring to the one with higher solute concentration
Hypotonic
in comparing two solutions, referring to the one with a lower solute concentration
Integral Proteins
typically a transmembrane protein with hydrophobic regions that completely spans the hydrophobic interior of the membrane
Ion Channel
a single protein or protein complex that traverses the lipid bilayer of cell membranes and form a channel to facilitate the movement of ions through the membrane according to their electrochemical gra
Isotonic
having the same solute concentration as another solution
Ligand
a molecule that binds specifically to a receptor site of another molecule
Membrane Potential
the change difference between a cell's cytoplasm and the extracellular fluid, due to the differential disribution of ions; membrane potential affects the activities of excitable cells and the transmem
Osmoregulation
the regulation of solute and water concentrations in body fluids by organisms living in hyperosmotic, hypoosmotic, and terrestrial environments
Osmosis
the diffusion of water across a selectively permeable membrane
Passive Transport
the diffusion of a substance across a biological membrane
Peripheral Proteins
a protein appendage loosely bound to the surface of a membrane and not embedded in the lipid bilayer
Phagocytosis
a type of endocytosis involving large, particulate substances, accomplished mainly by macrophages, neutrophils, and dendritic cells
Pinocytosis
a type of endocytosis in which the cell ingests extracellular fluid and its dissolved solutes
Plasmolysis
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
Proton Pump
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
Receptor-Mediated Endocytosis
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 a cell to acquir
Selective Permeability
a property of biological membranes that allows some substances to cross more easily than others
Sodium-Potassium Pump
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
Tonicity
the ability of a solution to cause a cell within it to gain or lose water
Transport Protein
a transmembrane protein that helps a certain substance or class of closely related substances to cross the membrane
Turgid
very firm; a walled cell becomes turgid if it has a greater solute concentration than its surroundings, resulting in entry of water
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