Which term refers to the energy-requiring process to move substances across membranes?

• A. Absorption
• B. Active Transport
• C. Distribution
• D. Pharmacokinetics

Answer: (B)

Energy-dependent movement of substances across membranes is achieved by active transport. This process uses cellular energy, typically ATP or existing ion gradients, to move molecules against their concentration or electrochemical gradient through specific transport proteins like pumps or transporters. That energy requirement is what sets it apart from other membrane transport processes. Absorption refers to uptake into the body and can involve passive or active steps but isn’t defined by the need for energy to cross membranes. Distribution describes how a drug spreads through body compartments after entry. Pharmacokinetics covers the overall processes of absorption, distribution, metabolism, and excretion. So the term that captures the energy-requiring movement across membranes is active transport.