1. ACTIVE TRANSPORT
Active transport – the transport of a substance across the cell membrane against its concentration gradient; because the movement of substances is against the concentration gradient it requires energy (ATP).
low concentration
high concentration

2. 1. Transport Proteins – are involved in moving substances against the concentration gradient, therefore they act as “pumps”
ex: the sodium-potassium pump transports 3 sodium ions out of the cell and 2 potassium ions into the cell against their concentration gradients

3. Sodium-Potassium Pump
out
Na+ is normally transported into the cell through an ion channel. in
(Cytoplasm)

4. **The Importance of the Sodium-Potassium Pump:
It helps maintain the concentration gradient of sodium and potassium ions across the cell membrane.
It prevents sodium from accumulating in the cell. If Na+ were not removed by the sodium-potassium pump water would enter the cell through osmosis and the cell would swell and eventually burst.
Sodium continuously diffuses into the cell through ion channels.

5. 2. Endocytosis – the movement of a substance into a cell by a vesicle; the cell membrane forms a pouch around a substance, the pouch then closes up and pinches off to form a vesicle, the substance is then carried into the cell
*sugar and polysaccharides are too large to be transported by carrier proteins so they are transported by endocytosis
ex: phagocytosis – the cell engulfs a
food particle or other solid substance
pinocytosis – the cell engulfs a water
particle or other liquid

6. Endocytos i s
(solids)
(liquids)

7. 3. Exocytosis – the movement of a substance by a vesicle to the outside of a cell, vesicles in the cell fuse with the cell membrane releasing their contents to the outside of the cell
ex: tear glands use exocytosis to excrete a salty solution containing proteins

8. Exocytosis

9. Endocytosis & Exocytosis