Here's why:
* Active transport moves substances against their concentration gradient, meaning from an area of low concentration to an area of high concentration. This movement requires energy because it is going against the natural tendency of molecules to move from high to low concentration.
* Passive transport, on the other hand, does not require energy. It relies on the natural movement of molecules down their concentration gradient. Examples include diffusion, osmosis, and facilitated diffusion.
Examples of active transport:
* Sodium-potassium pump: This pump actively moves sodium ions out of the cell and potassium ions into the cell, maintaining the cell's membrane potential and allowing for nerve impulses.
* Glucose uptake in the intestines: Glucose is transported from the intestines into the bloodstream against its concentration gradient, requiring energy.
* Proton pumps: These pumps move protons across membranes, generating a proton gradient that is used to drive other cellular processes.
Key takeaway: Active transport is the process that requires energy to move substances against their concentration gradient, ensuring cells maintain their internal environment and carry out essential functions.
