Homeostasis

Internal stability or "steady state" maintained by a cell or organism despite changes in the environment.

pH

A measure of how acidic or basic a solution is.

Buffer

Substance that maintains a fairly constant pH when an acid or base is added to it.

Diffusion

The movement of particles from an area of higher concentration to an area of lower concentration.

Passive Transport

Movement of materials into or out of a cell without the expenditure of energy.

Equilibrium

A state of balance.

Selectively Permeable

Allowing only some kinds of particles to pass through.

Osmosis

The passive transport of water across a selectively permeable membrane into a concentrated solution from a less concentrated solution.

Concentration Gradient

A difference in concentration on opposite sides of a plasma membrane.

Hypertonic

Having a higher concentration of solute outside a membrane than inside; water flows out of the cell.

Hypotonic

Having a higher concentration of solute inside a membrane than outside; water flows into the cell.

Isotonic

Having equal concentrations of a solute on both sides of a membrane; water flow is equal in both directions.

Facilitated Diffusion