Active transport
movement of substances across membranes using energy in the form of ATP.
ATP (adenosine triphosphate)
The energy molecule.
Concentration gradient
a gradient resulting from an unequal distribution of ions across the cell membrane.
Diffusion
passive movement of particles from a region of higher concentration to a region of lower concentration.
Endocytosis
the process in which the cell takes in materials from the outside by infolding of the membrane to form a vesicle.
Exocytosis
the process in which the cell releases materials to the outside by discharging them as membrane-bounded vesicles that pass through the cell membrane.
Facilitated diffusion
diffusion through a membrane that requires proteins.
Hypertonic
a more concentrated solution relative to another fluid.
Hypotonic
a less concentrated solution relative to another fluid.
Osmoregulation
control of the water balance of a living organism.
Osmosis
passive movement of water molecules from a region of lower solute concentration to a region of higher solute concentration.
Secretion
when material is released from a cell.
Semi-permeable membrane
membrane that allows some substances to diffuse through but not others. Transport pumps proteins in the plasma membrane that use ATP to move substances across the membrane. Vesicles a bubble-like membranous structure that stores and transports cellular pr