Active transport
Energy-requiring process that moves material across a cell membrane against a concentration difference.
Cell membrane
Thin, flexible barrier around a cell; regulates what enters and leaves the cell.
Cell wall
Strong supporting layer around the cell membrane in plants, algae, and some bacteria.
Concentration
The mass of solute in a given volume of solution, or mass/volume.
Diffusion
Process by which molecules tend to move from an area where they are more concentrated to an area where they are less concentrated.
Endocytosis
Process by which a cell takes material into the cell by infolding of the cell membrane.
Equilibrium
When the concentration of a solute is the same throughout a solution.
Exocytosis
Process by which a cell releases large amounts of material.
Facilitated diffusion
Movement of specific molecules across cell membranes through protein channels.
Hypertonic
When comparing two solutions, the solution with the greater concentration of solutes.
Hypotonic
When comparing two solutions, the solution with the lesser concentration of solutes.
Isotonic
When the concentration of two solutions is the same.
Lipid bilayer
Double-layered sheet that forms the core of nearly all cell membranes.
Osmosis
Diffusion of water through a selectively permeable membrane.
Phagocytosis
Process in which extensions of cytoplasm surround and engulf large particles and take them into the cell.
Pinocytosis
Process by which a cell takes in liquid from the surrounding environment.