Here's why:
* Active Transport: This process requires energy to move substances across the cell membrane *against* their concentration gradient (from a low concentration area to a high concentration area).
* Carrier Proteins: These proteins bind to specific molecules and facilitate their movement across the membrane.
* Pumping Action: The carrier proteins use energy, often from ATP, to change their shape and actively move molecules. This "pumping" action allows them to transport substances against their concentration gradient.
Therefore, "pump proteins" accurately describes their role in active transport, highlighting their ability to move molecules uphill, requiring energy to do so.
