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48 Cards in this Set

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Movement of molecules from one location to another because of random thermal molecular motion; net diffusion always occurs from a region of higher concentration to a region of lower concentration
Amount of a substance crossing a surface in a unit of time.
Net flux
Difference between two one-way fluxes
Diffusion equilibrium
State during which diffusion fluxes in opposite directions are equal; that is, the net flux equals zero.
Permeability constant, kp
Number that defines the proportionality between a flux and a concentration gradient and depends on the properties of the membrane and the diffusing molecule
Small passage in plasma membrane formed by integral membrane proteins and through which certain small-diameter molecules and ions can diffuse
Membrane potential
Voltage difference between inside and outside of cell
Electrochemical gradient
The driving force across a plasma membrane that dictates whether an ion will move into or out of a cell; it is established by both the concentration difference and the electrical charge difference between the cytosolic and extracellular surfaces of the membrane.
Channel gating
Process of opening and closing ion channels
Patch clamping
A procedure for isolating individual ion channels on the surface of a living cell and recording current through the channel.
Ligand-gated channels
Membrane channel operated by the binding of specific molecules to channel proteins
Voltage-gated channels
Cell-membrane ion channel opened or closed by changes in membrane potential.
Mechanically gated channels
Membrane ion channel that is opened or closed by deformation or stretch of the plasma membrane.
Integral membrane protein that mediates passage of molecule through membrane; also called carrier.
Movement of molecules across membrane by binding to protein transporter; characterized by specificity, competition, and saturation; includes facilitated diffusion and active transport.
Facilitated diffusion
System using a transporter to move molecules from high to low concentration across a membrane; energy not required.
Active transport
Energy-requiring system that uses transporters to move ions or molecules across a membrane against an electrochemical difference
Primary active transport
Active transport in which chemical energy is transferred directly from ATP to transporter protein.
Secondary active transport
Active transport in which energy released during transmembrane movement of one substance from higher to lower concentration is transferred to the simultaneous movement of another substance from lower to higher concentration.
Form of secondary active transport in which net movement of actively transported substance and “downhill” movement of molecule supplying the energy are in the same direction.
Form of secondary active transport in which net movement of actively transported molecule is in direction opposite “downhill” movement of molecule supplying the energy.
Protein membrane channel through which water can diffuse.
Net diffusion of water across a selective barrier from region of higher water concentration (lower solute concentration) to region of lower water concentration (higher solute concentration).
Total solute concentration of a solution; measure of water concentration in that the higher the solution osmolarity, the lower the water concentration.
1 mole of solute ions and molecules
Semipermeable membrane
Membrane permeable to some substances (usually water) but not to others (some solutes)
Osmotic pressure
Pressure that must be applied to a solution on one side of a membrane to prevent osmotic flow of water across the membrane from a compartment of pure water; a measure of the solution’s osmolarity.
Nonpenetrating solutes
Dissolved substances that do not passively diffuse across a plasma membrane.
Containing the same number of effectively nonpenetrating solute particles as normal extracellular fluid.
Solutions containing a lower concentration of effectively nonpenetrating solute particles than normal (isotonic) extracellular fluid.
Solutions containing a higher concentration of effectively membrane-impermeable solute particles than normal (isotonic) extracellular fluid.
Having the same total solute concentration as extracellular fluid.
Having total solute concentration greater than normal extracellular fluid.
Having total solute concentration less than that of normal extracellular fluid.
Process in which plasma membrane folds into the cell, forming small pockets that pinch off to produce intracellular, membrane-bound vesicles
Process in which intracellular vesicle fuses with plasma membrane, the vesicle opens, and its contents are liberated into the extracellular fluid.
Fluid endocytosis
Invagination of a plasma membrane by which a cell can engulf extracellular fluid.
Adsorptive endocytosis
Receptor-mediated invagination of plasma membranes by which both extracellular fluid and specific extracelluar molecules are moved into cytosol.
Endocytosis when the vesicle encloses extracellular fluid or specific molecules in the extracellular fluid that have bound to proteins on the extracellular surface of the plasma membrane.
Engulfment of particles by a cell.
Intracellular vesicles and tubular elements between Golgi apparatus and plasma membrane; sorts and distributes vesicles during endo- and exocytosis
Luminal membrane
Portion of plasma membrane facing the lumen; also called apical or mucosal membrane.
Basolateral membrane
Sides of epithelial cell other than luminal surface; also called serosal or blood side of cell
Paracellular pathway
The space between adjacent cells of an epithelium through which some molecules diffuse as they cross the epithelium
Transcellular pathway
Crossing an epithelium by movement into an epithelial cell, diffusion through the cytosol of that cell, and exit across the opposite membrane.
Exocrine gland
Cluster of epithelial cells specialized for secretion and having ducts that lead to an epithelial surface.
Endocrine gland
Group of epithelial cells that secrete into the extracellular space hormones that then diffuse into bloodstream; also called a ductless gland.
Chemical messenger synthesized by specific endocrine cells in response to certain stimuli and secreted into the blood, which carries it to target cells.