exocytosis Movement of substances out of the cell by a vesicle fusing with the plasma
membrane.
facilitated diffusion Diffusion in which a carrier protein physically moves the molecule
across the membrane; a form of passive transport.
homeostasis Maintaining a stable internal environment despite any external changes.
hypertonic solution Having a higher solute concentration than the cell; cell will lose
water by osmosis.
hypotonic solution Having a lower solute concentration than the cell; cell will gain water
by osmosis.
ion An atom that carries a negative or positive charge.
ion channel Protein in the plasma membrane that allows ions to pass through.
isotonic solution Asolutioninwhichtheamountofdissolvedmaterialisequalbothinside
and outside the cell; no net gain or loss of water.
osmosis Diffusion of water across a membrane.
passive transport Movement of molecules from an area of higher concentration to an area
of lower concentration; requires no energy.
phagocytosis Movement of large substances, including other cells, into the cell by vesicle
formation.
phospolipid A lipid molecule with a hydrophilic head and two hydrophobic tails; makes
up the cell membrane.
pinocytosis Movement of macromolecules into the cell by vesicle formation.
selectively permeable Semipermeable; property of allowing only certain molecules to
pass through the cell membrane.
sodium-potassium pump Carrier protein that moves sodium ions out of the cell and
potassium ions into the cell; works against the concentration gradient and requires
energy.
vesicle formation The formation of a small membrane-bound sac that can store and move
substances into and out of the cell.