The hormones that regulate plant growth are
A. ethylene and auxins
B. auxin and gibberellins
C. cytokinin and abscisic acid
D. ethylene and gibberellins
Hormones are internal chemical substances which assists living organisms in a specialized function, example of this function is growth in plants. Some hormones inhibit plant growth, while others expedite the same. By regulate, the examiner would mean control and not outright inhibition.
Now for the right answer to the above question:
- Ethylene is a plant hormone responsible for drooping and dropping of leaves, it is also responsible for ripening of fruits. Therefore, A is incorrect. Yes, auxins are known plant growth promoters, they promote the development of flowers and roots, but the presence of ethylene, which directly do not contribute to conventional growths renders this option wrong.
- Yes, gibberellins speed up germination and promote cell division and elongation. In addition to auxins, which have been established as true growth promoters, confirms an answer. B is very correct.
- Cytokinin is also a hormone known for cell division, a mixture of cytokinin and auxin is used to regulate the development of shoot and root system in plants. However, C is wrong because abscisic acid is a plant hormone which inhibits plant growth rather than promote same. By the term ‘regulate’ in the question, I would assume the examiner meant growth control and not outright inhibition.
- D is also incorrect; again, ethylene, though also a plant hormone isn’t responsible for conventional growth, but for ripening of fruits, drooping and dropping of leaves.
You may please note that:
- All the above mentioned options are valid plant hormones.
- Some of these hormones are not responsible for growth, but for some other function such as ripening of fruits, drooping and dropping of leaves, regulation of aging (cytokinin).
Use the questions and answers session to raise further questions on this topic…
/ culled from 2017 JAMB-UTME biology question 2 /