The most important plant hormone is

1. Analyze the question The question asks which plant hormone is considered the most important. The options are four major plant growth regulators.

2. Explain the concept Plant hormones (growth regulators) control growth and responses to the environment:

• Auxin (IAA): Promotes cell elongation, phototropism and geotropism, apical dominance, root initiation, and fruit development. It is also the first plant hormone discovered.
• Cytokinin: Promotes cell division and delays leaf senescence (ageing).
• Gibberellin: Promotes stem elongation, seed germination, and breaking of dormancy.
• Abscisic acid (ABA): An inhibitor. It causes stomatal closure, seed dormancy, and leaf fall in stress conditions.

3. Solution

• Abscisic acid mainly inhibits growth, so it is not the main growth hormone.
• Cytokinin and gibberellin have important but more specific roles (cell division and stem elongation or germination).
• Auxin has the widest range of effects. It controls tropisms, apical dominance, root formation, and fruit growth, and it interacts with the other hormones. This is why textbooks and JAMB treat it as the most important plant hormone.

4. Answer The correct option is C. auxin.

5. Exam tip Remember: "Auxin is A-number one." When a question asks for the "most important" or "main growth" hormone, think auxin. Link the others to a keyword: cytokinin = cell division, gibberellin = germination and tall stems, abscisic acid = stress and stomatal closure.