Auxin drives plant growth through cell elongation

Steps:

• Identify auxin as a key plant hormone regulating growth and development.
• Recall its primary function: promoting cell elongation in shoots via acid growth hypothesis.
• Evaluate choices against known roles—auxin influences tropisms and apical dominance, not meiosis or germination.
• Confirm A matches auxin's role in stem elongation for upward growth.

Why A is correct:

• Auxin stimulates proton pumps to acidify cell walls, loosening them for turgor-driven elongation per the acid growth theory.

Why the others are wrong:

• B: Meiotic division is regulated by hormones like cytokinins, not auxin.
• C: Auxin inhibits lateral root branching at high concentrations, promoting main root growth.
• D: Seed germination is primarily stimulated by gibberellins, not auxin.

Final answer: A