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passive transport

the movement of substances across a cell membrane without the use of energy by the cell


the movement of particles from regions of higher density to regions of lower density

concentration gradient

a difference in the concentration of a substance across a distance


a state that exists when the concentration of a substance is the same throughout a space


diffusion of molecules through a semipermeable membrane from a place of higher concentration to a place of lower concentration until the concentration on both sides is equal


describes a solution whose solute concentration is lower than the solute concentration inside a cell


describes a solution whose solute concentration is higher than the solute concentration inside a cell


describes a solution whose solute concentration is equal to the solute concentration inside a cell

contractile vacuole

in protists, an organelle that accumulates water and then releases it periodically to maintain osmotic pressure

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


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


the bursting of a cell

facilitated diffusion

the transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins

carrier protein

a protein that transports substances across a cell membrane.

ion channel

a complex of protein molecules in a cell membrane that form a pore through which ions can pass

active transport

the movement of chemical substances, usually across the cell membrane, against a concentration gradient; requires cells to use energy

sodium potassium pump

a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell


the process by which a cell membrane surrounds a particle and encloses the particle in a vesicle to bring the particle into the cell


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


a method of active transport across the cell membrane in which the cell takes in extracellular fluids


the process by which a cell engulfs large particles or whole cells, either as a defense mechanism or as a means to obtain food


a cell that ingests and destroys (digests) foreign matter or microorganisms


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

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