Active transport requires cells to use energy in the form of ATP to move substances against their concentration gradient, such as the sodium-potassium pump transporting sodium and potassium ions across nerve cell membranes. The sodium-potassium pump uses ATP to pump 3 sodium ions out and 2 potassium ions into the cell against their gradients. Transport proteins also use active transport for molecules too large to pass through the membrane on their own, such as during endocytosis and exocytosis.

13. TYPES OF TRANSPORT MOLECULES: UNIPORT SYMPORT ANTIPORT Antiport transports the solute in (or out) and the co-transported solute the opposite direction. One goes in the other goes out or vice-versa. Symport transports the solute and a cotransported solute at the same time in the same direction. Uniport transports one solute at a time.

22. ENDOCYTOSIS & EXOCYTOSIS

23. Phagocytosis refers to the process of engulfing large particles. PHAGOCYTOSIS??