CIE AS Biology (9700) exams from 2022

Revision Notes

4.2.3 Active Transport

The Process of Active Transport

  • Active transport is the movement of molecules and ions through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration
  • Active transport requires carrier proteins (each carrier protein being specific for a particular type of molecule or ion)
  • Although facilitated diffusion also uses carrier protein, active transport is different as it requires energy
  • The energy is required to make the carrier protein change shape, allowing it to transfer the molecules or ions across the cell membrane
  • The energy required is provided by ATP (adenosine triphosphate) produced during respiration
  • In the diagram below, molecules or ions are being pumped into the cell against a concentration gradient
  • Active transport is important in:
    • Reabsorption of useful molecules and ions into the blood after filtration into the kidney tubules
    • Absorption of some products of digestion from the digestive tract
    • Loading sugar from the photosynthesising cells of leaves into the phloem tissue for transport around the plant
    • Loading inorganic ions from the soil into root hairs

Exam Tip

Be careful not to get carrier proteins and channel proteins confused when answering questions on active transport. Active transport requires carrier proteins (transmembrane transport proteins that undergo conformational change) not channel proteins.


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