Which process uses cellular energy to move substances against their concentration gradient?

The process that uses cellular energy to move substances against their concentration gradient is known as primary active transport. In this process, energy, typically from ATP, is utilized to transport molecules across a membrane from an area of lower concentration to an area of higher concentration. This is essential for maintaining cellular functions and concentrations of ions, nutrients, and other substances that cells need to operate effectively.

Primary active transport specifically involves the use of transport proteins, often called pumps, which can change shape when energy is supplied, allowing them to move substrates in a direction that contradicts natural diffusion tendencies. For instance, the sodium-potassium pump is a classic example of primary active transport, where sodium ions are expelled from the cell while potassium ions are brought in against their respective concentration gradients.

In contrast, facilitated diffusion and simple diffusion do not require cellular energy; they utilize concentration gradients to allow substances to move from high to low concentration naturally. Passive processes encompass these types of transport, where the movement is driven by already existing gradients without the need for additional energy input. Therefore, the distinction lies in the requirement of energy to drive movement against the concentration gradient, which is a fundamental characteristic of primary active transport.