Final answer:
Active transport uses carrier proteins to move molecules against a concentration gradient, requiring energy in the form of ATP, as seen in the sodium-potassium pump of nerve cells.
Step-by-step explanation:
The process that uses proteins to move molecules against a concentration gradient is known as active transport. During active transport, carrier proteins or pumps use energy, usually in the form of ATP (adenosine triphosphate), to move substances from an area of low concentration to an area of high concentration. This is crucial for maintaining the necessary concentrations of ions and other substances for cell function, despite the passive movements that tend to even out concentrations.
Examples include the sodium-potassium pump in nerve cells, which is essential for transmitting messages to the brain.