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

Isotonic

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

Facilitated Diffusion

The movement of substances across a plasma membrane with the aid of protein molecules embedded in the membrane