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 ChannelsIon 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 DiffusionIn facilitated diffusion, a carrier protein transports a substance across the cell membrane down the concentration gradient of the substance

Active Transport

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

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

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

Exocytosis

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

Communications between Cells

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