1. Transport across the cell membrane Active Transport Active Transport – requires energy in the form of ATP (Na+K+ pump, endocytosis & exocytosis) Passive Transport Passive Transport – no energy required (diffusion, osmosis, facilitated diffusion)

2. Active transport is responsible for cells containing relatively high concentrations of potassium ions but low concentrations of sodium ions. The mechanism responsible for this is the sodium-potassium pump which moves these two ions in opposite directions across the plasma membrane.

3. Concentrations of Na+ and K+ ions on the two sides of the membrane are interdependent = same carrier protein transports both ions. The carrier is an ATP-ase and it pumps 3 sodium ions out of the cell for every 2 potassium ions pumped in.

4. Function of the pump resting potentialresting potential The Na+/K+-pump helps maintain resting potential that assist s transport & regulates cell volume resting potential sodiumsodium low concentration of sodium ions within cellsodium potassiumpotassium high levels of potassium ions within the cellpotassium

5. Cells need to bring in substances (glucose, amino acids) by facilitated diffusion Carrier proteins combine with and transport substances across the cell membrane Possible because active transport maintains a concentration gradient Facilitated Diffusion

6. Movement of sodium from one side of a cell membrane to the other side creates an osmotic gradient that drives the absorption of water. Water diffuses back into the cell carrying needed substances Osmosis

7. Endocytosis & Exocytosis Larger substances are moved into & out of the cell by vesicle formation Requires ATP