Movements Into and Out of the Cell (3.3) Terms

Passive mechanisms

Processes that move substances across the cell membrane without requiring cellular energy (ATP)

Active mechanisms

Processes that use cellular energy (ATP) to move substances across the cell membrane

Diffusion

The movement of atoms

Concentration gradient

The difference in concentration of a substance between two regions.

Diffusional equilibrium

The state where the concentration of a substance is uniform throughout a solution.

Facilitated diffusion

Diffusion in which a carrier molecule or ion channel helps a substance cross the cell membrane.

Osmosis

The movement of water across a selectively permeable membrane toward a higher concentration of non-permeable solute.

Isotonic

A solution that has the same osmotic pressure as body fluids

Hypertonic

A solution with a higher osmotic pressure than body fluids

Hypotonic

A solution with a lower osmotic pressure than body fluids

Filtration

A process that forces molecules through membranes by exerting pressure.

Active transport

The movement of substances from a region of lower concentration to a region of higher concentration using carrier molecules and ATP.

Endocytosis

The process by which a cell membrane envelops a substance and draws it into the cell in a vesicle.

Pinocytosis

A type of endocytosis where a cell engulfs droplets of liquid.

Phagocytosis

A type of endocytosis where a cell engulfs solid particles

Receptor-mediated endocytosis

A selective form of endocytosis where specific molecules bind to receptors on the cell membrane before being taken in.

Exocytosis

The process by which a vesicle fuses with the cell membrane to release its contents outside the cell.

Transcytosis

A process that combines endocytosis and exocytosis to selectively and rapidly transport a substance across a cell.