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