Introduction: Plant hormones (phytohormones) like auxin, gibberellin, cytokinin, ethylene, abscisic acid, jasmonic acid and salicylic acid regulate growth, development and secondary metabolite production. For B. Pharm students, understanding their biosynthesis, signaling mechanisms (e.g., TIR1, GID1, PYR/PYL), transport (polar auxin transport), synthetic analogs (2,4‑D, NAA, BAP) and inhibitors (NPA, paclobutrazol) is essential for pharmacognosy, tissue culture, elicitation of medicinal compounds and post‑harvest applications. This topic links plant physiology with pharmaceutical applications such as micropropagation, optimizing bioactive compound yield and herbicidal action. The MCQs below probe mechanisms, receptor biology, biochemical pathways and applied uses relevant to pharmacy practice. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. What class of molecule is auxin and what is its principal naturally occurring form in plants?
- Terpenoid; gibberellic acid
- Amino‑acid derivative; indole‑3‑acetic acid
- Phenolic compound; salicylic acid
- Fatty acid derivative; jasmonic acid
Correct Answer: Amino‑acid derivative; indole‑3‑acetic acid
Q2. Which protein complex mediates auxin‑dependent degradation of Aux/IAA repressors?
- SCF (Skp1‑Cullin‑F‑box) complex with TIR1 F‑box receptor
- Proteasome activated by ACC oxidase
- Histidine kinase receptor complex (AHK2/AHK3)
- GID1‑DELLA polyubiquitination complex
Correct Answer: SCF (Skp1‑Cullin‑F‑box) complex with TIR1 F‑box receptor
Q3. Polar auxin transport is primarily facilitated by which transporter family?
- AUX/LAX influx and PIN efflux carrier families
- ABC transporters only
- GLUT transporter family
- G‑protein coupled receptors (GPCRs)
Correct Answer: AUX/LAX influx and PIN efflux carrier families
Q4. Which hormone commonly induces seed germination by mobilizing endosperm reserves?
- Abscisic acid (ABA)
- Gibberellin (GA)
- Ethylene
- Cytokinin
Correct Answer: Gibberellin (GA)
Q5. The GA receptor in plants is known as:
- TIR1
- GID1
- ETR1
- PYL
Correct Answer: GID1
Q6. Which hormone primarily mediates stomatal closure under drought stress?
- Cytokinin
- Abscisic acid (ABA)
- Auxin
- Brassinosteroid
Correct Answer: Abscisic acid (ABA)
Q7. Which enzyme is rate‑limiting in ethylene biosynthesis from S‑adenosylmethionine?
- ACC synthase (ACS)
- ACC oxidase (ACO)
- Polyphenol oxidase
- RuBisCO
Correct Answer: ACC synthase (ACS)
Q8. 2,4‑D is used in agriculture as which of the following?
- Growth retardant inhibiting gibberellin biosynthesis
- Auxinic herbicide causing uncontrolled growth in broadleaf weeds
- Ethylene inhibitor to delay fruit ripening
- Fungicide targeting cell wall synthesis
Correct Answer: Auxinic herbicide causing uncontrolled growth in broadleaf weeds
Q9. Which cytokinin is commonly used in tissue culture to stimulate shoot proliferation?
- Benzylaminopurine (BAP)
- Indole‑3‑acetic acid (IAA)
- Gibberellic acid (GA3)
- Abscisic acid (ABA)
Correct Answer: Benzylaminopurine (BAP)
Q10. DELLA proteins are key regulators in which hormone signaling pathway?
- Auxin signaling
- Gibberellin signaling as growth repressors
- Ethylene perception
- Jasmonic acid biosynthesis
Correct Answer: Gibberellin signaling as growth repressors
Q11. Which receptor family perceives abscisic acid (ABA) to initiate stress responses?
- Pyl/Pyr/RCAR family of cytosolic receptors
- GID1 membrane receptor
- ETR1 membrane histidine kinase
- TIR1 F‑box receptor
Correct Answer: Pyl/Pyr/RCAR family of cytosolic receptors
Q12. Jasmonic acid (JA) is particularly important in plants for:
- Regulation of photoperiodic flowering only
- Defense against herbivores and induction of secondary metabolites
- Promoting seed dormancy
- Stomatal opening during drought
Correct Answer: Defense against herbivores and induction of secondary metabolites
Q13. Which compound is an inhibitor of gibberellin biosynthesis used to produce dwarf phenotypes?
- Paclobutrazol
- 2,4‑D
- NAA (naphthaleneacetic acid)
- BAP (benzylaminopurine)
Correct Answer: Paclobutrazol
Q14. Salicylic acid (SA) plays a central role in:
- Systemic acquired resistance and defense against biotrophic pathogens
- Cell elongation in stems
- ABA‑mediated stomatal closure
- Auxin polar transport
Correct Answer: Systemic acquired resistance and defense against biotrophic pathogens
Q15. In micropropagation, a high auxin:cytokinin ratio generally favors:
- Shoot induction and proliferation
- Root initiation and callus formation
- Flower induction
- Somatic embryogenesis inhibition
Correct Answer: Root initiation and callus formation
Q16. Which hormone is primarily associated with the “triple response” in etiolated seedlings?
- Ethylene causing inhibited elongation, radial swelling and exaggerated apical hook
- Gibberellin causing stem elongation
- Cytokinin causing shoot proliferation
- Abscisic acid causing stomatal closure
Correct Answer: Ethylene causing inhibited elongation, radial swelling and exaggerated apical hook
Q17. Which synthetic auxin is commonly used to stimulate root formation in cuttings?
- Paclobutrazol
- Naphthaleneacetic acid (NAA)
- Gibberellic acid (GA3)
- Ethylene
Correct Answer: Naphthaleneacetic acid (NAA)
Q18. Which signaling component is a coreceptor for jasmonate perception involved in ubiquitin‑mediated degradation?
- COI1 F‑box protein as part of SCFCOI1 receptor complex
- TIR1 receptor for auxin
- PYL ABA receptor
- ETR1 ethylene receptor
Correct Answer: COI1 F‑box protein as part of SCFCOI1 receptor complex
Q19. Fluridone is used experimentally to block which biosynthetic pathway?
- Ethylene biosynthesis via ACC oxidase inhibition
- Abscisic acid (ABA) biosynthesis by inhibiting phytoene desaturase
- Auxin biosynthesis by blocking tryptophan aminotransferase
- Gibberellin biosynthesis by inhibiting ent‑kaurene oxidase
Correct Answer: Abscisic acid (ABA) biosynthesis by inhibiting phytoene desaturase
Q20. Cross‑talk between salicylic acid (SA) and jasmonic acid (JA) pathways typically results in:
- Complete synergism enhancing both responses equally
- Antagonistic interaction where SA suppresses JA responses for biotrophic vs necrotrophic defence partitioning
- JA converting into SA through beta‑oxidation
- No interaction; pathways are independent
Correct Answer: Antagonistic interaction where SA suppresses JA responses for biotrophic vs necrotrophic defence partitioning
Q21. Brassinosteroids primarily act through which type of receptor at the plasma membrane?
- Receptor serine/threonine kinase BRI1
- F‑box protein receptor
- G‑protein coupled receptor
- Histidine kinase receptor only found in bacteria
Correct Answer: Receptor serine/threonine kinase BRI1
Q22. Which hormone treatment is routinely used to synchronize or induce flowering or fruit set in horticulture?
- Cytokinin sprays to induce rooting
- Gibberellin sprays to induce flowering and fruit set in some crops
- Paclobutrazol to accelerate fruit ripening
- Fluridone to promote germination
Correct Answer: Gibberellin sprays to induce flowering and fruit set in some crops
Q23. What is a common pharmacological application of ethylene in post‑harvest handling?
- Used to delay ripening and extend shelf life
- Applied to accelerate fruit ripening and uniform maturation
- Used as a systemic fungicide
- Applied to increase alkaloid synthesis in roots
Correct Answer: Applied to accelerate fruit ripening and uniform maturation
Q24. Which plant hormone promotes cell division in conjunction with auxin during organogenesis?
- Cytokinin
- Abscisic acid (ABA)
- Ethylene
- Salicylic acid (SA)
Correct Answer: Cytokinin
Q25. Which statement about auxin transport inhibitors like NPA (n‑1‑naphthylphthalamic acid) is correct?
- They enhance polar auxin transport to accelerate growth
- They block auxin efflux carriers leading to altered developmental patterns
- They are gibberellin biosynthesis stimulators
- They mimic cytokinin action in tissue culture
Correct Answer: They block auxin efflux carriers leading to altered developmental patterns
Q26. Application of jasmonic acid or its methyl ester in culture is primarily used to:
- Suppress secondary metabolite production
- Elicit production of defense‑related secondary metabolites in medicinal plants
- Induce seed dormancy
- Inhibit root formation
Correct Answer: Elicit production of defense‑related secondary metabolites in medicinal plants
Q27. Which hormone is most directly associated with leaf senescence and abscission?
- Cytokinin delays senescence; ethylene promotes senescence and abscission
- Gibberellin initiates senescence
- Auxin promotes abscission by itself
- Brassinosteroids are the primary senescence hormones
Correct Answer: Cytokinin delays senescence; ethylene promotes senescence and abscission
Q28. In the context of pharmacognosy, manipulating phytohormones can increase yield of:
- Non‑bioactive structural carbohydrates only
- Medicinal secondary metabolites such as alkaloids, phenolics and terpenoids
- Only volatile oils with no effect on alkaloids
- Inorganic mineral content exclusively
Correct Answer: Medicinal secondary metabolites such as alkaloids, phenolics and terpenoids
Q29. The primary signaling mechanism shared by many plant hormones involves which cellular process?
- Ubiquitin‑mediated proteasomal degradation of transcriptional repressors
- Direct DNA methylation by hormones
- Permanent insertion of hormone genes into the genome
- Hormone‑activated ion channel opening only
Correct Answer: Ubiquitin‑mediated proteasomal degradation of transcriptional repressors
Q30. For B. Pharm students interested in producing plant‑derived drugs, which hormone strategy is most useful in in vitro culture to enhance biomass and metabolite production?
- Use of balanced auxin and cytokinin ratios with elicitors like methyl jasmonate and salicylic acid to stimulate secondary metabolite biosynthesis
- Exclusive application of high concentrations of ABA to maximize growth
- Complete removal of hormones to force differentiation only
- Rely solely on ethylene treatments to increase root biomass
Correct Answer: Use of balanced auxin and cytokinin ratios with elicitors like methyl jasmonate and salicylic acid to stimulate secondary metabolite biosynthesis
I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.
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