Which of the following processes is a form of active transport?

Active transport is a biological process that moves molecules against their concentration gradient, which requires energy, typically in the form of ATP. The sodium-potassium pump is a prime example of active transport because it actively moves sodium ions out of the cell and potassium ions into the cell. This pump plays a crucial role in maintaining the electrochemical gradient essential for various cellular functions, such as nerve impulse transmission and muscle contraction.

In contrast, osmosis is a type of passive transport that involves the movement of water across a semipermeable membrane until an equilibrium is reached. Facilitated diffusion also represents a passive transport process that allows molecules to cross membranes with the assistance of transport proteins, without the expenditure of energy. Protein synthesis, while a complex metabolic process, does not classify as a form of transport, whether active or passive, but rather refers to the creation of proteins through transcription and translation involving ribosomes. Thus, the sodium-potassium pump distinctly illustrates active transport due to its energy requirement and function of moving ions against their concentration gradients.