Active Transport Active Transport – the movement of materials from a low concentration to a high concentration, which requires energy, or ATP. I. Cell Pumps – special carrier proteins that require energy to pump substances against a concentration gradient (low to high). A. How Cell Pumps Work 1. Carrier Protein (pump) binds to a specific molecule. 2. The protein changes shape (when ATP is available), protecting the molecule and moving it through the cell membrane. 3. The protein releases molecule & returns to its original shape. *It’s the same as facilitated diffusion, except molecules are being pumped from a low concentration to a high concentration with the use of ATP. B. An Example of a Cell Pump: The Sodium-Potassium Pump 1. Many animal cells require a high concentration of sodium on the outside of the cell, and high concentrations of potassium on the inside of the cell. II. Endocytosis vs. Exocytosis The transporting of macromolecules, large food particles, and other large substances that cannot use carrier proteins. Also can be used to move large quantities of smaller molecules. Requires energy, or the use of ATP. A. Endocytosis – moving substances into the cell, even other smaller cells. 1. How it Works A portion of the cell membrane moves inward, forming a pouch. Molecules enter this pouch & the membrane continues pinching inward, eventually completely surrounding the molecules. The pouch pinches off completely from the cell membrane and becomes a vesicle. 2. Pinocytosis – the endocytosis of liquids 3. Phagocytosis - the endocytosis of solids or whole cells B. Exocytosis - releasing substances to the outside of the cell 1. How it Works A Vesicle from inside the cell starts to merge or fuse with the cell membrane. Once completely fused, the contents of the vesicle are released to the outside. Membrane of the vesicle is now a part of the cell membrane. 2. Some vesicles are made by the Golgi Apparatus and contain proteins that need to leave the cell.