CAIE A Level Biology 9700 · Transport in plants
A student is examining transverse sections of a herbaceous dicotyledonous plant and observes the structure of xylem vessel elements and phloem sieve tube elements.
Compare the structure of xylem vessel elements and phloem sieve tube elements in such plants. In your answer, explain why a sieve tube element requires an adjacent companion cell.
7 marks, so the mark scheme is looking for about 7 separate creditworthy points. Making the same point twice in different words earns it once.
Compare means: Give similarities or differences between two things, and say which side each point belongs to. Write each point as a pair, for example: A is X, whereas B is Y. Two separate descriptions rarely earn the marks.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.