The Fluid Mosaic Model of the Cell Membrane

Getting Materials In and Out of Cells

The Phospholipid Bilayer is Semi Permeable

Some molecules can diffuse freely through membranes, while others require assistance from membrane proteins (facilitated diffusion). These two methods allow materials to flow along their concentration gradient. Since NO energy is required, this is called passive transport. Some molecules must enter the cell against their concentration gradient (eg. glucose). This requires protein pumps which use ATP for energy. Since energy is required, this is called active transport.

Osmosis: The Diffusion of Water

Exocytosis