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 4 high concentration 9

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

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

**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.

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

IN Fluid or Liquid

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

Exocytosis OUT

IN OUT

Endocytosis & Exocytosis