Final answer:
Carrier proteins are involved in both facilitated diffusion and active transport. In facilitated diffusion, they allow the movement of substances without ATP. In active transport, they move substances against concentration gradients using ATP.
Step-by-step explanation:
Carrier proteins are involved in both facilitated diffusion and active transport. In facilitated diffusion, carrier proteins allow the movement of substances from an area of higher concentration to an area of lower concentration, without requiring ATP. These proteins are less selective and allow the transportation of various molecules. On the other hand, in active transport, carrier proteins or pumps are responsible for moving substances against their concentration gradients, from a low concentration to a high concentration, and this process requires ATP. Active transport carrier proteins are more selective and can transport specific ions or molecules.