CAIE A Level Biology 9700 · Transport in plants
A student adds a blue dye to the water surrounding the roots of a young bean plant. After 30 minutes, a cross-section of the root is examined under a microscope. The dye is observed in the cell walls of the cortex but is absent from the endodermal cell walls. Outline how water moves from the soil into the root and then to the xylem, comparing the apoplast and symplast pathways. In your answer, explain the role of the Casparian strip in this process.
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.
Written by Markquill to follow the Cambridge International syllabus. Markquill is independent and is not affiliated with or endorsed by Cambridge International.