COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for CSIR-UGC NET/JRF, SLET, GATE, and other entrance tests: PLANT PHYSIOLOGY – Plant Hormones.
Syllabus Outline
- Biosynthesis, storage, breakdown and transport of plant hormones (e.g. auxins, gibberellins, cytokinins, abscisic acid, ethylene, brassinosteroids, jasmonates, salicylic acid, and strigolactones)
- Physiological roles, signalling pathways, and mechanisms of action of plant hormones.
- Role of plant hormones in regulating responses to biotic and abiotic stresses.
- Synergistic interactions among different plant hormones.
This quiz contains 25 concept-based, most frequently asked MCQs on “PLANT PHYSIOLOGY – Plant Hormones”. Each question has a single correct/most appropriate answer.
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1. In the absence of Abscisic Acid, the protein responsible for maintaining the subclass III SnRK2 kinases in an inactive state is:
A) PYL/RCAR receptor
B) B-type Response Regulator (ARR-B)
C) Group A Protein Phosphatase 2C (PP2C)
D) Indole-3-acetic acid
2. Which plant hormone signalling pathway utilises dephosphorylation of its key nuclear transcription factor as the primary activation mechanism, leading to nuclear accumulation of the transcription factor rather than receptor-mediated degradation of a nuclear repressor?
A) Auxin
B) Gibberellin
C) Brassinosteroids
D) Jasmonate
3. Which of the following components acts as a key negative regulator (GSK3-like kinase) of the Brassinosteroids signalling pathway, maintaining transcription factors BZR1/BES1 in an inactive, cytoplasmic/degradation-prone state in the absence of the hormone?
A) ETR1
B) CTR1
C) BIN2
D) MAX2
4. Which molecular event immediately follows the binding of Ethylene to its receptor (ETR1/ERS) in the endoplasmic reticulum membrane?
A) Activation of the constitutive triple response 1 (CTR1) kinase.
B) Activation of the transcription factor EIN3 by phosphorylation.
C) Inactivation of the CTR1 kinase by receptor dimerisation.
D) Ubiquitination and degradation of the EIN3 repressor.
5. A gain-of-function mutant of a D53-like SMXL repressor protein, which is resistant to ubiquitination and degradation by the Strigolactone pathway, is generated in Arabidopsis. What is the predicted phenotype concerning shoot architecture?
A) Reduced shoot branching (compact rosette).
B) Increased shoot branching (highly bushy phenotype).
C) Wild-type branching phenotype, but decreased lateral root formation.
D) Dwarfism and delayed flowering.
6. Considering the antagonistic relationship observed in many signalling pathways, if a plant lacks the capacity to synthesise Strigolactones, which major developmental process would be constitutively enhanced?
A) Stomatal closure
B) Seed dormancy
C) Shoot branching
D) Flowering time
7. The most widely accepted major biosynthetic route for Indole-3-acetic acid in higher plants involves which intermediate pathway?
A) Indole-3-pyruvic acid pathway
B) Tryptamine pathway
C) Indole-3-acetonitrile pathway
D) Methylerythritol phosphate pathway
8. The primary chemical inhibitor used to study polar auxin transport that works by directly associating with and inhibiting the activity of PIN efflux carriers is:
A) Paclobutrazol
B) N-1-naphthylphthalamic acid
C) Salicylic acid
D) Abscisic acid
9. If a researcher applies the transport inhibitor N-1-naphthylphthalamic acid symmetrically to the tip of a maize coleoptile and then exposes the coleoptile to unilateral blue light, what is the predictable physiological outcome?
A) The coleoptile bends towards the light, but the curvature is enhanced compared to the control.
B) The coleoptile bends away from the light due to the lack of an asymmetrical auxin gradient.
C) The coleoptile fails to bend, remaining straight due to the lack of an asymmetrical auxin gradient.
D) The coleoptile undergoes the triple response due to increased Ethylene production.
10. Which set of phytohormones are chemically categorised primarily as terpenoid derivatives?
A) Auxins and Ethylene
B) Gibberellins and Abscisic acid
C) Cytokinins and Salicylic acid
D) Jasmonates and Brassinosteroids
11. The ability of the root apex to sense and grow away from areas of high salinity relies fundamentally on the rapid redistribution of which specific Auxin efflux carrier protein?
A) DELLA
B) TIR1
C) PIN2
D) MAX2
12. A key evolutionary aspect of Auxin biology is its polar transport mechanism. Which statement accurately describes the function of Auxin Influx Carriers relative to Efflux Carriers?
A) Influx carriers are constitutively active; efflux carriers are regulated by phosphorylation.
B) Influx carriers are located apically; efflux carriers are located basally, maintaining directionality.
C) Efflux carriers facilitate the movement of protonated Indole-3-acetic acid into the cell; influx carriers move anionic Indole-3-acetic acid out of the cell.
D) Influx carriers facilitate the movement of protonated Indole-3-acetic acid into the cell; efflux carriers move anionic Indole-3-acetic acid out of the cell.
13. Polar transport of Auxin is crucial for developmental patterning. Which protein family is essential for actively mediating the efflux of the Indole-3-acetic acid anion out of the plant cell?
A) LAX
B) TIR
C) PIN
D) ARF
14. A researcher generates an Arabidopsis line that constitutively overexpresses the GH3.17 gene, which encodes an Indole-3-acetic acid-amino acid synthetase responsible for Auxin conjugation and inactivation. What phenotype is most likely to be observed in the root meristem?
A) Larger root meristem size due to enhanced effective free Auxin concentration.
B) Smaller root meristem size due to reduced effective free Auxin concentration.
C) Increased sensitivity to Cytokinin application.
D) A constitutive triple response phenotype.
15. Strigolactones regulate the number of lateral shoots by repressing the transcription factor BRANCHED1 (BRC1), which itself inhibits shoot outgrowth. The primary function of Strigolactone signalling is therefore generally seen as:
A) Promoting vegetative growth and cell expansion.
B) Inducing flowering and senescence.
C) Inhibiting shoot branching and regulating root-mycorrhizal symbiosis.
D) Mediating seed dormancy and stomatal closure.
16. A dominant mutant is isolated with a constitutively active TOR kinase (CA-TOR), meaning TOR activity cannot be downregulated. When this CA-TOR mutant is subjected to severe drought stress, what is the most probable outcome compared to the wild-type?
A) Enhanced stomatal closure and increased stress tolerance due to constitutive growth suppression.
B) Reduced Abscisic Acid signalling sensitivity and failure to halt growth, leading to poor survival.
C) Constitutive activation of SnRK2, regardless of Abscisic Acid presence.
D) Accumulation of DELLA proteins and dwarfism.
17. Under conditions of hypoxia (waterlogging), plants often promote the formation of adventitious roots and aerenchyma tissue to increase oxygen retention. Which phytohormone is primarily responsible for triggering these adaptive changes?
A) Cytokinin
B) Abscisic Acid
C) Ethylene
D) Auxin
18. Ethylene is implicated in modulating salinity stress tolerance. Experimental studies have shown that exogenous application of the Ethylene precursor 1-aminocyclopropane-1-carboxylic acid can enhance salinity tolerance, largely by:
A) Inhibiting the breakdown of Na+/K+
B) Increasing Reactive Oxygen Species accumulation in the cytosol.
C) Inducing antioxidant defence systems and maintaining nutrient uptake.
D) Promoting Abscisic Acid synthesis, which mediates stress tolerance.
19. A PIN2 null mutant is placed under unilateral salinity stress. How would its root growth response likely differ from the wild type?
A) The wild-type root would bend towards the salt, but the PIN2 mutant would bend away.
B) The PIN2 mutant root would fail to bend away from the salt due to the inability to establish the required asymmetrical Auxin gradient.
C) Both wild-type and PIN2 mutant roots would continue normal vertical growth, as PIN2 is irrelevant for salinity responses.
D) The PIN2 mutant would exhibit a constitutive triple response due to increased Ethylene sensitivity.
20. Which of the following phytohormones are known to synergistically promote cell elongation and stem growth, often leading to enhanced dwarfism when both pathways are functionally impaired?
A) Gibberellins and Brassinosteroids
B) Gibberellins, Brassinosteroids, and Abscisic Acid
C) Brassinosteroids, Abscisic Acid and Ethylene
D) Gibberellins and Ethylene
21. Identify the correct physiological role for the corresponding phytohormone:
I – Strigolactones: Inhibition of shoot branching.
II – Cytokinin: Delaying leaf senescence.
III – Abscisic acid: Promotion of seed dormancy and stomatal closure.
IV – Ethylene: Regulation of fruit ripening and the triple response in seedlings.
A) I, III, and IV
B) I, II, and III
C) I, II, III, and IV
D) II and IV only
22. Consider a homozygous mutant line of Arabidopsis that cannot synthesise Gibberellins. Which of the following phenotypic defects would be expected?
I – Severe dwarfism
II – Failure of stamen development and pollen production
III – Delayed or abolished flowering in long-day plants
IV – Constitutive triple response phenotype
A) I and III only
B) I, II, and III
C) II and IV only
D) I, III, and IV
23. Which of the following molecular components act as negative regulators in the Cytokinin signalling and homeostasis system?
I – Type-A Response Regulators
II – Cytokinin oxidase/dehydrogenase
III – Histidine Phosphotransfer proteins
IV – Type-B Response Regulators
A) I and II only
B) I, II, and III
C) I, II, and IV
D) II, III, and IV
24. An antagonistic interaction between Auxin and Cytokinin controls the maintenance of the root apical meristem size. Cytokinin typically limits root apical meristem size by:
I – Promoting the expression of the auxin degradation gene GH3.
II – Decreasing the expression of auxin influx carriers AUX1 and LAX2 in the root stem cell niche.
III – Inducing the degradation of Aux/IAA repressors.
IV – Promoting the expression of WOX5 in the Quiescent Centre.
A) I and II only
B) I, II, and III
C) II, III, and IV
D) I, II, and IV
25. Assertion (A): The antagonistic relationship between Auxin and Cytokinin creates distinct gradients, essential for establishing the Quiescent Centre and the Transition Zone in the root.
Reason (R): High Auxin promotes cell division near the tip, while high Cytokinin acts slightly further up, reducing auxin sensitivity by decreasing Auxin influx carrier expression, thereby promoting differentiation.
A) Both (A) and (R) are true, and (R) is the correct explanation for (A).
B) Both (A) and (R) are true, but (R) is NOT the correct explanation for (A).
C) (A) is true, but (R) is false.
D) (A) is false, but (R) is true.
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References
- Hopkins, W. G., & Hüner, N. P. A. (2008). Introduction to Plant Physiology, John Wiley & Sons. 4th Edition.
- Pandey, S. N., & Sinha, B. K. (2015). Plant Physiology, Vikas Publishing House. 4th Edition.
- Jain, V. K. (2018). Fundamentals of Plant Physiology, S. Chand Publishing. 20th Edition.
- Verma, Mohit & Verma, S. K. (2022). A Textbook of Plant Physiology, Biochemistry and Biotechnology, S. Chand Publishing. 13th Edition.
- Lincoln Taiz, Ian Max Møller, Angus Murphy, and Eduardo Zeiger (2022). Plant Physiology and Development, Oxford University Press, 7th Edition.
- Nelson, David L. & Cox, Michael M. (2021). Lehninger Principles of Biochemistry, W. H. Freeman, 8th Edition.
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