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active transport
the movement of chemical substances, usually
across the cell membrane, against a
concentration gradient; requires cells to use
energy
carrier protein
a protein that transports substances across a cell
membrane
concentration gradient
a difference in the concentration of a substance
across a distance
contractile vacuole
in protozoans, an organelle that accumulates
water and then releases it periodically to
maintain osmotic pressure
cytolysis
the bursting of a cell
diffusion
the movement of particles from regions of higher
density to regions of lower density
endocytosis
the process by which a cell membrane surrounds
a particle and encloses the particle in a vesicle
to bring the particle into the cell
equilibrium
in biology, a state that exists when the
concentration of a substance is the same
throughout a space
exocytosis
the process by which a substance is released
from the cell through a vesicle that transports the
substance to the cell surface and then fuses with
the membrane to let the substance out
facilitated diffusion
the transport of substances through a cell
membrane along a concentration gradient with
the aid of carrier proteins
hypertonic
describes a solution whose solute concentration is
higher than the solute concentration inside a cell
hypotonic
describes a solution whose solute concentration is
lower than the solute concentration inside a cell
ion channel
a pore in a cell membrane through which ions
can pass
isotonic
describes a solution whose solute concentration is
equal to the solute concentration inside a cell
osmosis
the diffusion of water or another solvent from a
more dilute solution (of a solute) to a more
concentrated solution (of the solute) through a
membrane that is permeable to the solvent
passive transport
the movement of substances across a cell
membrane without the use of energy by the cell
phagocyte
a cell that ingests and destroys (digests) foreign
matter or microorganisms
phagocytosis
the process by which a cell engulfs large particles
or whole cells, either as a defense mechanism or
as a means to obtain food
pinocytosis
a method of active transport across the cell
membrane in which the cell takes in extra cellular
fluids
plasmolysis
the contraction or shrinking of the cell membrane
of a plant cell in a hypertonic solution in response
to the loss of water by osmosis
sodium-potassium pump
a carrier protein that uses ATP to actively
transport sodium ions out of a cell and potassium
ions into the cell
turgor pressure
the pressure that is exerted on the inside of cell
walls and that is caused by the movement of
water into the cell
vesicle
a small cavity or sac that contains materials in a
eukaryotic cell; forms when part of the cell
membrane surrounds the materials to be taken
into the cell or transported within the cell