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CAIE A-Level Biology 7.2.7 Companion Cells and Assimilate Loading

Practise explaining ATP-driven proton pumping, proton–sucrose cotransport into companion cells and transfer through plasmodesmata into sieve-tube elements.

Syllabus
2028–2030
Course
Biology 9700
Level
AS

Exam points

  • use ATP to pump protons from companion cells and create an electrochemical gradient
  • explain proton return with sucrose through a cotransporter as secondary active transport
  • trace assimilate transfer from companion cell into adjacent sieve-tube elements

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