CAIE A Level Biology 9700 · Transport in plants
In a plant, sucrose produced in leaf mesophyll cells must be loaded into phloem sieve tubes for transport to sinks. Companion cells adjacent to sieve tubes play a key role in this process. Outline how companion cells use proton pumps and cotransporter proteins to load sucrose into sieve tubes.
4 marks, so the mark scheme is looking for about 4 separate creditworthy points. Making the same point twice in different words earns it once.
Outline means: Give the main points briefly. Less detail than describe, but every key step has to be there. One short line per step, in order. The marks are for coverage, not depth.
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