Here's why:
* Active transport moves molecules against their concentration gradient, meaning from a region of lower concentration to a region of higher concentration. This movement requires energy because it goes against the natural flow of molecules, which would normally move from high to low concentration.
* ATP (adenosine triphosphate) is the primary energy currency of cells. Active transport systems utilize the energy released from the breakdown of ATP to power the movement of molecules across the membrane.
Examples of active transport include:
* Sodium-potassium pump: This pump moves sodium ions out of the cell and potassium ions into the cell, both against their concentration gradients.
* Proton pumps: These pumps move protons (H+ ions) across membranes, establishing a proton gradient that can be used to drive other processes, such as ATP synthesis.
* Glucose uptake: The transport of glucose into cells can also be an active process, particularly in cells with high glucose demands, such as brain cells.
Key takeaway: Active transport is the only type of membrane transport that directly uses ATP as an energy source.
