use of a plasma membrane carrier protein to move a molecule or ion from a region of lower concentration to one of higher concentration; it opposes equilibrium and requires energy.
junction between cells in which the adjacent plasma membranes do not touch but are held together by intercellular filaments attached to buttonlike thickenings
protein that combines with and transports a molecule or ion across the plasma membrane.
structure that surrounds a plant, protistan, fungal, or bacterial cell and maintains the cell's shape and rigidity
protein that forms a channel to allow a particular molecule or ion to cross the plasma membrane
one of the major lipids found in animal plasma membranes; makes the membrane impermeable to many molecules.
in animal cells, shriveling of the cell due to water leaving the cell when the environment is hypertonic
ability of plasma membranes to regulate the passage of substances into and out of the cell, allowing some to pass through and preventing the passage of others.
movement of molecules or ions from a region of higher to lower concentration; it requires no energy and tends to lead to an equal distribution
process by which substances are moved into the cell from the environment by phagocytosis (cellular eating) or pinocytosis (cellular drinking); includes receptor mediated endocytosis
process in which an intracellular vesicle fuses with the plasma membrane so that the vesicle's contents are released outside the cell.
passive transfer of a substance into or out of a cell along a concentration gradient by a process that requires a carrier.
model for the plasma membrane based on the changing location and pattern of protein molecules in a fluid phospholipid bilayer
junction between cells formed by the joining of two adjacent plasma membranes; it lends strength and allows ions, sugars, and small molecules to pass between cells.
lipid in plasma membranes that bears a carbohydrate chain attached to a hydrophobic tail.
higher solute concentration (less water) than the cytoplasm of a cell; causes cell to lose water by osmosis.
Lower solute (more water) concentration than the cytoplasm of a cell; causes cell to gain water by osmosis
solution that is equal in solute concentration to that of the cytoplasm of a cell; causes cell to neither lose nor gain water by osmosis
measure of the tendency of water to move across a differentially permeable membrane; visible as an increase in liquid on the side of the membrane with higher solute concentration
process by which amoeboid-type cells engulf large substances, forming an intracellular vacuole.
in plants, cytoplasmic strands that extend through pores in the cell wall and connect the cytoplasm of two adjacent cells.
selective uptake of molecules into a cell by vacuole formation after they bind to specific receptor proteins in the plasma membrane
protein located in the plasma membrane or within the cell; binds to a substance that alters some metabolic aspect of the cell.
carrier protein in the plasma membrane that moves sodium ions out of and potassium ions into animal cells; important in nerve and muscle cells
junction between cells when adjacent plasma membrane proteins joint to form an impermeable barrier.
osmolarity of a solution compared to that of a cell. If the solution is isotonic to the cell, there is no net movement o f water; if the solution is hypotonic the cell gains water; and if the solution is hypertonic, the cell loses water.