A biology student placed a germinating broad bean seed horizontally in a dark chamber to investigate gravitropism in roots. After 24 hours, the student observed that the primary root had bent downwards towards gravity, as shown in the diagram below.
Which of the following statements, A to D, correctly explains this physiological response?
Auxin accumulates on the lower side of the root, inhibiting cell elongation on this side.
Auxin accumulates on the lower side of the root, stimulating cell elongation on this side.
Auxin accumulates on the upper side of the root, inhibiting cell elongation on this side.
Gibberellins accumulate on the upper side of the root, stimulating cell division on this side.
