PASSIVE AND ACTIVE TRANSPORT IN CELLS

Passive Transport Movement across the cell membrane that does not require the cell’s energy

Concentration Gradient A difference in concentration of a substance throughout a space

Equilibrium Concentration of a substance is equal throughout a space

Diffusion Movement of a substance from an area of high concentration to an area of low concentration

Selectively Permeable Membrane Only allows some substances to pass through

Diffusion Through Ion Channels A transport protein with a polar pore that allows ions to diffuse into and out of the cell The electrical charge of an ion can affect its ability to diffuse- The inside of a typical cell is negative, so it is more likely a positive ion will diffuse into the cell and a negative ion will diffuse out. Opposites attract and like charges repel

Carrier Proteins Most cells have a different kind of protein that can bind to a specific substance on one side of the cell membrane and carry it to the other side

Facilitated Diffusion Carrier proteins are used to transport specific substances without using the cell’s energy

OSMOSIS Diffusion of water across a selectively permeable membrane Hypertonic- water diffuses out of cell- cell shrinks Hypotonic- water diffuses into cell- cell swells Isotonic- water diffuses into and out of cells at equal rates

Active Transport Movement of a substance across the cell membrane against the concentration gradient – against diffusion i.e. from low to high concentration REQUIRES ENERGY from the cell supplied by ATP http://www.phschool.com/science/biology_place/biocoach/biomembrane1/diffusion.html

VESICLES Substances that are too large to be transported by carrier proteins, such as proteins and polysaccharides, are moved across the membrane by vesicles Endocytosis- movement of a substance into a cell by a vesicle Exocytosis- movement of a substance out of a cell by a vesicle

Endocytosis

Exocytosis

Endocytosis and Exocytosis

Receptor Proteins Cells must also respond to important information and filter out unimportant information. To receive messages sent by signal molecules, cell membranes contain specialized proteins called receptor proteins that bind to the signal molecules allowing the cell to respond to the signal