Emergency Medical Technician (EMT) Intermediate Practice Exam

What is the term for the movement of a substance against a concentration gradient?

1. Simple diffusion

2. Osmosis

3. Facilitated diffusion

4. Active transport

The correct answer is: Active transport

Active transport refers to the movement of a substance across a cell membrane against its concentration gradient, which means that it moves from an area of lower concentration to an area of higher concentration. This process requires energy, typically derived from adenosine triphosphate (ATP), because it is working against the natural tendency of substances to move from high to low concentration. In contrast to active transport, simple diffusion involves the movement of molecules from an area of higher concentration to an area of lower concentration without the use of energy. Osmosis specifically refers to the movement of water across a semipermeable membrane and also occurs down a concentration gradient. Facilitated diffusion, on the other hand, is a form of passive transport that utilizes specific proteins to help move substances across a membrane, still following the concentration gradient and not requiring energy. Thus, active transport is distinct in that it requires energy to move substances against their natural flow.