Which process requires energy to move substances against their concentration gradient?

Active transport is the correct process that requires energy to move substances against their concentration gradient. This means that during active transport, molecules are transported from an area of lower concentration to an area of higher concentration, which is contrary to the natural direction of diffusion where substances move from higher to lower concentrations.

This process typically utilizes ATP (adenosine triphosphate) as the energy source to power transport proteins in the cell membrane. These proteins can be specific for certain molecules, allowing for selective uptake or expulsion of substances vital for the cell’s functions, such as ions, glucose, and amino acids.

In contrast, diffusion, facilitated diffusion, and osmosis do not require energy because they rely on the natural kinetic movement of molecules to achieve equilibrium. Diffusion allows substances to move freely along their concentration gradient, while facilitated diffusion uses a transport protein but still moves substances down their gradient. Osmosis specifically refers to the movement of water across a semipermeable membrane and similarly follows its concentration gradient.