Passive and Active Transport Movement of material into and out of cells

Passive transport is the movement of substances across the cell membrane without the use of energy by the cell

Diffusion is the movement of a substance from an area of high concentration to an area of lower concentration

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

Ion Channels Ion channels are proteins that have a pore through which ions can cross the cell membrane. Ions cannot diffuse across the cell membrane due to the lipid bi-layer. Ion channels move ions from an area of high ion concentration to an area of low ion concentration (down the ion’s concentration gradient).

Facilitated Diffusion In facilitated diffusion, a carrier protein transports a substance across the cell membrane down the concentration gradient of the substance

Active transport is the movement of a substance against the concentration gradient of the substance. Active transport requires cells to use energy Active Transport

Sodium-Potassium Pump In animal cells, the sodium-potassium pump uses energy supplied by ATP to transport sodium ions out of the cell and potassium ions into the cell Sodium-Potassium Pump

Endocytosis Click for video of Endocytosis and Exocytosis During endocytosis, substances are moved into a cell by a vesicle that pinches off from the cell membrane Endocytosis

During exocytosis substances inside a vesicle are released from a cell as the vesicle fuses with the cell membrane Exocytosis

Communications between Cells Communication between cells often involves signal molecules that are bound by receptor proteins Communications between Cells