Here's why:
* Energy requirement: Active transport moves molecules against their concentration gradient, meaning from an area of low concentration to an area of high concentration. This process requires energy, usually supplied by ATP (adenosine triphosphate).
* Transport proteins: Active transport relies on specialized transport proteins embedded in the cell membrane. These proteins bind to the molecules being transported and use energy to move them across the membrane.
In contrast to active transport, passive transport:
* Doesn't require energy: It moves molecules down their concentration gradient, from an area of high concentration to an area of low concentration.
* Doesn't require transport proteins: It can occur directly through the membrane or with the help of channel proteins.
Examples of active transport include:
* Sodium-potassium pump: This vital pump moves sodium ions out of the cell and potassium ions into the cell, maintaining the cell's electrochemical gradient.
* Glucose uptake: Cells use active transport to take in glucose even when its concentration is lower outside the cell.
Therefore, active transport is the process that relies on energy and transport proteins to move molecules across the cell membrane against their concentration gradient.
