Which is an example of active transport?

• A. Diffusion
• B. Facilitated diffusion
• C. Active transport
• D. Filtration

Answer: (C)

Active transport is a vital process in cellular biology that involves the movement of substances across a cell membrane against their concentration gradient, meaning that molecules move from an area of lower concentration to an area of higher concentration. This process requires energy, typically in the form of ATP, because it works against the natural tendency for substances to move from high to low concentration.

In this context, active transport itself is the correct example being asked about. Unlike diffusion and facilitated diffusion, which are passive processes that do not require energy and rely on the inherent kinetic energy of molecules to move down their concentration gradients, active transport explicitly requires energy input. Filtration, while also a form of transport, typically relies on pressure differences rather than energy invested by the cell.

Active transport's role is crucial for maintaining essential concentrations of ions, nutrients, and other substances within cells, ensuring that cells can regulate their internal environment regardless of external conditions. For example, the sodium-potassium pump is a classic model of active transport, where sodium ions are pumped out of the cell while potassium ions are pumped in, both against their concentration gradients, using ATP.