Question

Which of the following is a plant growth regulator?

• A. Auxin
• B. Cytokinin
• C. Gibberellin
• D. All of these Correct Answer: (D) All of these

Hint:

To easily master the five primary Plant Growth Regulators for your biology exams, split them into two clear functional groups: 1. The Promoters (Growth Boosters): Auxins, Gibberellins, and Cytokinins. 2. The Inhibitors (Stress Responders): Abscisic Acid (ABA) and Ethylene. This functional breakdown helps you spot them instantly in any multiple-choice list!

Answer 1

The Correct Option is D

Step 1: Understanding the Concept:
Plant Growth Regulators (PGRs), also widely known as phytohormones, are simple, small chemical molecules produced in minute quantities by plant tissues. They travel throughout the plant body to control, alter, and regulate various physiological and developmental processes—such as cell division, elongation, seed dormancy, flowering, fruit ripening, and leaf fall.

Step 2: Detailed Explanation:
Let's examine the primary functions of each chemical substance listed in the options: - (A) Auxin: The first discovered plant hormone, primarily synthesized at growing shoot tips. It plays a critical role in apical dominance, cell elongation, and phototropic bending. - (B) Cytokinin: A hormone that promotes active cytokinesis (cell division). It is found in abundance in areas undergoing rapid division, such as root apexes and developing coconut milk, and helps delay leaf senescence. - (C) Gibberellin: A vast family of acidic hormones that promote internodal stem elongation, break seed dormancy, and induce bolting (sudden elongation of stems) in rosette plants. Since Auxin, Cytokinin, and Gibberellin are all major classes of naturally occurring phytohormones that regulate plant development, they collectively fit the definition of plant growth regulators. This makes option (D) the correct choice.

Step 3: Final Answer:
All of the listed options (Auxin, Cytokinin, and Gibberellin) are plant growth regulators.