Vocabulary

active transport

The energy-requiring process of pumping molecules and ions across membranes against a concentration gradient.

carrier protein

A transport protein that is specific for an ion, molecule, or group of substances; carries the ion or molecule across the membrane by changing shape after the binding of the ion or molecule.

channel protein

A transport protein that acts like a pore in the membrane that lets water molecules or small ions through quickly.

contractile vacuole

A type of vacuole that removes excess water from a cell.

diffusion

The movement of molecules from an area of high concentration of the molecules to an area with a lower concentration.

endocytosis

The process of capturing a substance or particle from outside the cell by engulfing it with the cell membrane.

exocytosis

The process of vesicles fusing with the plasma membrane and releasing their contents to the outside of the cell.

facilitated diffusion

The diffusion of solutes through transport proteins in the plasma membrane.

gated channel protein

A transport protein that opens a "gate," allowing a molecule to flow through the membrane.

ion channel

A protein that transports ions across the membrane by facilitated diffusion.

ligand

A small molecule that binds to a larger molecule.

osmosis

The diffusion of water molecules across a selectively permeable membrane from an area of higher concentration to an area of lower concentration.

passive transport

A way that small molecules or ions move across the cell membrane without input of energy by the cell.

second messenger

A small molecule that starts a change inside a cell in response to the binding of a specific signal to a receptor protein.

selectively permeable

The characteristic of the cell membrane that allows certain molecules to pass through the membrane, but not others.

signal-transduction pathway

The signaling mechanism by which a cell changes a signal on it surface into a specific response inside the cell; most often involves an ordered sequence of chemical reactions inside the cell which is carried out by enzymes and other molecules.

sodium-potassium pump

A carrier protein that moves sodium and potassium ions against large concentration gradients, moves two potassium ions into the cell where potassium levels are high, and pumps three sodium ions out of the cell and into the extracellular fluid.

transport protein

A protein that completely spans the membrane, and allows certain molecules or ions to diffuse across the membrane; channel proteins, gated channel proteins, and carrier proteins are three types of transport proteins that are involved in facilitated diffusion.