What is Active transport?
Topic: Active transport
Answer
ACTIVE TRANSPORT is the movement of molecules or ions across a cell membrane AGAINST the concentration gradient — from a region of lower concentration to one of higher — using ENERGY supplied by ATP and carrier proteins in the membrane.
Two elements must appear, and each is worth a mark: AGAINST the concentration gradient, and requiring ENERGY.
THE CONTRAST with passive processes makes the definition clear: DIFFUSION and OSMOSIS move substances DOWN the gradient, from high to low concentration, and need NO energy — like water flowing downhill. ACTIVE TRANSPORT moves them UP the gradient and therefore needs energy — like pumping water uphill.
WHY PLANTS NEED IT: soil often contains a LOWER concentration of a mineral than the root cell already holds. Diffusion would move the mineral out of the root, not in. Active transport is the only way a plant can go on absorbing such minerals, and it is why root cells contain many mitochondria — they need the ATP.