Movement of Substances

Movement of materials in and out of cells

Cells allow for the movement of materials across the plasma membranes through either passive process or active processes.

Passive Process – Where substances flow across plasma membranes without the expenditure of energy. The following are examples of passive processes:

  • Diffusion – Where a high concentration of a substance will diffuse to areas of low concentration
  • Facilitated Diffusion – Another type of diffusion, accomplished with the assistance of integral proteins in the membrane that serves as a carrier
  • Osmosis – Is the net movement of water molecules from an area of high water concentration to low
  • Bulk flow – The movement of a large number of substances/materials in the same direction as a result of other processes forces that push them
  • Filtration – This process involves the movement of solvents and dissolved substances across a membrane by gravity or mechanical pressure
  • Dialysis – The separation of small molecules from large molecules by diffusion across a membrane

Active Process – When cells actively participate in moving substances across membranes by expending energy. Examples include:

  • Active Transport – The process where substances are moved across a membrane typically from an area of low concentration to high
  • Endocytosis – Where segments of the plasma membrane enclose around a substance and brings it into the cell
  • Exocytosis – The opposite of endocytosis where the cell expels a substance