Movement of Substances (Terms)

Selectively Permeable Membrane

A Selectivley Permeable Membrane allows only specific substances to pass.


The substance whose movement is being described may be water.


The substance dissolved in the water.

Down the Concentration Gradient

Movement of substances may occur from higher to lower concentration.

Against the Gradient

The reverse of Down the Concentration Gradient.


A higher concentration of solutes.


An equal concentration of solutes.

Passive or Active Movement

Active movement requires the expenditure of energy and usually up a gradient.

Bulk Flow

Bulk flow is the collective movement of substances in the same direction in response to a force or pressure.

Passive Transport Processes


Diffusion is the net movement of substances from an area of higher concentration to an area of lower concentration.


Osmosis is the diffusion of water molecules across a selectively permeable membrane.


Dialysis is the diffusion of solutes across a selectively permeable membrane.


Plasmolysis is the movement of water out of a cell (osmosis) that results in a collapse of the cell.

Facilitated Diffusion

Facilitated diffusion is the diffusion of solutes through channel proteins in the plasma membrane.

Countercurrent Exchange

Countercurrent Exchange describes the diffusion of substances between two regions in which substances are moving by bulk flow in opposite directions.

Vesicular Transport

  • Exocytsis
  • Endocytosis
  1. Phagocytosis
  2. Pinocytosis
  3. Receptor-mediated Endocytosis