CAIE A Level Biology 9700 · Transport in plants
A researcher studying phloem transport in a flowering plant observes that treating leaves with an inhibitor of plasma membrane H+-ATPases (proton pumps) causes a rapid decrease in the concentration of sucrose in the sieve tubes of the phloem. Outline the mechanism by which sucrose is loaded into sieve tubes, including the roles of companion cells, proton pumps, and cotransporter proteins.
6 marks, so the mark scheme is looking for about 6 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.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.