[Campbell Biology P.910] Which of the following statements accurately describes the mechanis... | Practice Question

Which of the following statements accurately describes the mechanism of positive gravitropism in plant roots, according to the statolith hypothesis?

  • A: Statoliths accumulate on the upper side of root cap cells, promoting cell elongation there.
  • B: Auxin accumulates on the lower side of the root, where it inhibits cell elongation, causing the upper side to grow faster.
  • C: Calcium and auxin are transported to the upper side of the root, stimulating rapid cell division.
  • D: Statoliths directly stimulate cell division in the root's zone of elongation, leading to downward growth.

Explanation

According to the statolith hypothesis, statoliths settle to the lower side of root cap cells, triggering a redistribution of calcium and auxin. Auxin accumulates on the lower side of the root's zone of elongation. At high concentrations, auxin inhibits cell elongation, causing the upper side of the root to elongate faster and the root to bend downward.