lesson
Some transport works against a concentration difference
1 · Learn
Diffusion produces net movement down a concentration gradient. Active transport can move substances against that gradient using energy supplied by cellular processes and appropriate membrane proteins.
A cell does not use active transport for every movement. The mechanism depends on the substance, membrane and concentration conditions.
2 · Worked example
Root cells can take up some mineral ions from a lower external concentration into a higher internal concentration by active transport.
3 · Your turn
Why cannot simple diffusion explain sustained movement from lower to higher concentration in this example?
Check your answer
That direction is against the concentration gradient and requires an energy-dependent mechanism.
4 · Apply your learning
Compare two concentration diagrams and identify which proposed movement needs an additional energy source.
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