Why Does Active Transport Require Energy?
Part of Cell Transport — GCSE Biology
This how it works covers Why Does Active Transport Require Energy? within Cell Transport for GCSE Biology. Diffusion, osmosis, active transport, factors affecting transport, surface area to volume ratio, and practical investigations It is section 9 of 18 in this topic. Use this how it works to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 9 of 18
Practice
18 questions
Recall
20 flashcards
⚙️ Why Does Active Transport Require Energy?
Diffusion and osmosis are passive — particles naturally move from where there are many of them to where there are fewer. They are following the laws of physics, like water running downhill. No energy input is needed because the movement is "downhill" along the concentration gradient.
Active transport, however, moves substances against the concentration gradient — from an area of LOW concentration to an area of HIGH concentration. This is the equivalent of pumping water uphill. Just as a pump needs electricity to force water upwards, the cell needs energy to force molecules against their natural tendency.
This energy comes from ATP (adenosine triphosphate), which is produced by mitochondria during aerobic respiration. Carrier proteins (also called pump proteins) in the cell membrane use the energy from ATP to change shape, physically grabbing molecules on one side of the membrane and releasing them on the other side — against the gradient.
This is why cells that rely heavily on active transport (e.g. root hair cells absorbing mineral ions, kidney tubule cells reabsorbing glucose) are packed with large numbers of mitochondria. More mitochondria = more ATP = more capacity for active transport.
By contrast, diffusion needs no membrane proteins and no ATP — it occurs spontaneously whenever a concentration gradient exists.
Key Exam Point — Grade 7-9
Quick Check: Root hair cells absorb mineral ions from the soil even when the concentration of minerals in the soil is lower than inside the cell. Which type of transport is used? How do you know?
Active transport. The mineral ions are moving from an area of LOW concentration (soil) to an area of HIGH concentration (inside the cell) — this is against the concentration gradient. Only active transport can move substances against a gradient, and it requires ATP from mitochondria to do so. Root hair cells have many mitochondria to provide this energy.