Campbell Biology in Focus Chapter 5

selective permeability

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

amphipathic

having both a hydrophilic region and a hydrophobic region

fluid mosaic model

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

integral protein

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)

peripheral protein

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

glycolipid

a lipid with one or more covalently attached carbohydrates

glycoprotein

a protein with one or more covalently attached carbohydrates

transport protein

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

channel protein

a type of transport protein that functions by having a hydrophilic channel that certain molecules or atomic ions use as a tunnel through a membrane

aquaporin

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

carrier protein

a type of transport protein that holds onto its passengers and changes shape in a way that shuttles them across a membrane

diffusion

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

concentration gradient

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

passive transport

the diffusion of a substance across a biological membrane with no expenditure of energy

osmosis

the diffusion of free water molecules across a selectively permeable membrane

tonicity

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

isotonic

referring to a solution that has the same concentration of solute and free water as outside the cell, causes no net movement of water into or out of the cell

hypertonic

referring to a solution that has a higher solute concentration and lower free water than inside the cell, will cause the cell to lose waterand shrink

hypotonic

referring to a solution that has a lower solute concentration and higher free water than inside the cell, will cause the cell to take in water and swell

osmoregulation

regulation of solute concentration and water balance by a cell or organism

turgor pressure

a back pressure exerted by a cell wall that occurs when the cell swells

turgid

swollen or distended, as in plant cells occurs in a walled cell if it has a lower water potential than its surroundings, resulting in entry of water

flaccid

limp lacking turgor (stiffness or firmness), as in a plant cell in surroundings where there is a tendency for water to leave the cell occurs in a walled cell if it has a higher water potential than its surroundings, resulting in the loss of water

plasmolysis

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

facilitated diffusion

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

ion channel

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

gated channel

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

active transport

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

sodium

potassium pump

membrane potential

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

electrochemical gradient

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)

electrogenic pump

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

proton pump

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

cotransport

the coupling of the "downhill" diffusion of one substance to the "uphill" transport of another against its own concentration gradient

exocytosis

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

endocytosis

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

phagocytosis

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)

pinocytosis

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

receptor

mediated endocytosis