Stress Physiology of Plants: Important MCQs

COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for CSIR-UGC NET/JRF, SLET, GATE, and other entrance tests: PLANT PHYSIOLOGY – Stress Physiology of Plants.

Syllabus Outline

1. Types of stress and corresponding plant responses.
2. Biotic stresses (e.g., pathogens and insects) and abiotic stresses (e.g., water, temperature, and salinity).
3. Plant responses to pathogens, parasites, and competitors.
4. Plant responses to flooding and drought conditions.
5. Plant responses to high and low temperature stresses.
6. Plant responses to high salinity stress.
7. Plant responses to mineral deficiency and toxicity stresses.
8. Plant responses to oxidative stress caused by reactive oxygen species (e.g., H₂O₂).

This quiz contains 25 concept-based, most frequently asked MCQs on “PLANT PHYSIOLOGY – Stress Physiology of Plants”. Each question has a single correct/most appropriate answer.

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1. In higher plants, each reaction of the shikimate pathway is catalysed by a separate enzyme, whereas in fungi, five reactions are catalysed by a multifunctional enzyme complex. What is this fungal enzyme complex called?

A) AROM complex

B) Shikimate synthase

C) Chorismate mutase

D) Pentafunctional oxidase

2. Which of the following statements correctly describes SnRK2 kinases?

A) They act as negative regulators of abscisic acid signalling.

B) They are activated through dephosphorylation.

C) They are activated when PP2C inhibition is relieved.

D) They function exclusively in roots under drought conditions.

3. During drought stress, Abscisic Acid accumulation triggers stomatal closure primarily through:

A) Activation of plasma-membrane H⁺-ATPase

B) Efflux of K⁺ and anions from guard cells

C) Uptake of Ca²⁺ into vacuoles

D) Degradation of actin filaments

4. Which statement best explains Abscisic acid-induced gene regulation?

A) It represses transcription.

B) It acts via cAMP-dependent protein kinases.

C) It activates transcription factors through phosphorylation.

D) It signals bypasses transcriptional control.

5. Which reactive oxygen species is most stable and commonly measured as an indicator of oxidative stress in plants?

A) Hydroxyl radical (•OH)

B) Singlet oxygen (¹O₂)

C) Hydrogen peroxide (H₂O₂)

D) Superoxide anion (O₂•–)

6. The enzyme superoxide dismutase converts superoxide radicals to:

A) Water and oxygen

B) Hydroxyl radicals

C) Singlet oxygen

D) Hydrogen peroxide and oxygen

7. Which antioxidant enzyme decomposes hydrogen peroxide in peroxisomes?

A) Catalase

B) Glutathione peroxidase

C) Ascorbate peroxidase

D) Peroxidase

8. In plants, reactive oxygen species production mainly occurs at:

A) PSI and PSII electron-transport chains

B) Cell wall peroxidases

C) Glycolysis

D) Vacuoles

9. Which compound directly scavenges hydroxyl radicals in plant cells?

A) Proline

B) Sucrose

C) Glutathione

D) β-Carotene

10. Salicylic acid accumulation during biotic stress is mainly synthesised via which pathway?

A) Mevalonate pathway

B) Terpenoid pathway

C) Shikimate-independent pathway

D) Isochorismate pathway

11. Which molecule acts as a mobile signal in systemic acquired resistance in plants?

A) Jasmonic acid methyl ester

B) Auxin

C) Cytokinin

D) Methyl salicylate

12. Small heat-shock protein protects plants from heat injury primarily by:

A) Denaturing aggregated proteins

B) Stabilising and refolding partially denatured proteins

C) Inhibiting reactive oxygen species generation

D) Blocking membrane transport

13. Plants tolerant to drought often accumulate osmoprotectants such as proline. The major function of proline under stress is:

A) Osmotic adjustment and reactive oxygen species scavenging

B) Acting as a respiratory substrate

C) Hormone signalling to stop evapotranspiration during the night

D) Electron generated during the light reaction for the photolysis of water are absorbed by proline

14. During flooding, the accumulation of ethylene in submerged tissues promotes:

A) Reduction in aerenchyma formation

B) Elongation of petioles and adventitious roots

C) Suppression of antioxidant enzymes

D) Abscisic acid biosynthesis to regulate stress

15. Salt stress causes both osmotic and ionic stress in plants. The major toxic ion contributing to ionic stress is:

A) K⁺

B) Mg²⁺

C) Ca²⁺

D) Na⁺

16. The Salt Overly Sensitive pathway mitigates Na⁺ toxicity by activating:

A) Vacuolar H⁺-ATPase

B) Salt-porin

C) Chloride channel

D) Plasma membrane Na⁺/H⁺ antiporter

17. The compatible solute glycine betaine protects the photosynthetic machinery by:

A) Inhibiting chlorophyll degradation

B) Stabilising the oxygen-evolving complex and thylakoid membranes

C) Acting as a transcriptional repressor

D) Decreasing stomatal aperture

18. Highlight stress in chloroplasts causes over-reduction of the electron transport chain, leading to:

A) Decreased ROS generation

B) Chlorophyll synthesis

C) Formation of nitric oxide

D) Increased production of singlet oxygen (¹O₂) at PSII

19. Photorespiration helps plants under stress by:

A) Producing secondary metabolites to protect plants

B) Acting as a sink for excess reducing power

C) Increasing water loss to eliminate excess photon energy

D) Enhancing metabolic activities to minimise the accumulation of intermediate metabolites

20. Abscisic acid and ethylene often show antagonistic interaction during:

A) Seed dormancy maintenance

B) Stomatal closure under drought

C) Leaf abscission

D) Fruit ripening

21. The “stress memory” phenomenon in plants refers to:

A) Epigenetic and metabolic imprinting enabling faster response to recurrent stress

B) Genetic mutations due to stress, enabling faster response to recurrent stress

C) Permanent gain of stress tolerance

D) Silencing of stress-inducing gene enabling faster response to recurrent stress

22. Calcium acts as a secondary messenger in plant stress signalling by:

A) Binding to transcription factors

B) Modulating protein kinases

C) Enhance the specificity of photoreceptors

D) Co-factor of reactive oxygen species production in chloroplasts

23. The primary detoxification site for reactive nitrogen species is:

A) Chloroplast

B) Mitochondria and peroxisomes

C) Endoplasmic Reticulum

D) Vacuole

24. Which osmoprotectant primarily accumulates in halophytes and contributes to ionic balance without interfering with enzyme activity?

A) Sucrose

B) Proline

C) Glycine betaine

D) Trehalose

25. Which hormone is most closely linked to root-to-shoot signalling under water deficit?

A) Ethylene

B) Salicylic acid

C) Abscisic acid

D) Cytokinin

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References

1. Hopkins, W. G., & Hüner, N. P. A. (2008). Introduction to Plant Physiology, John Wiley & Sons. 4th Edition.
2. Pandey, S. N., & Sinha, B. K. (2015). Plant Physiology, Vikas Publishing House. 4th Edition.
3. Jain, V. K. (2018). Fundamentals of Plant Physiology, S. Chand Publishing. 20th Edition.
4. Verma, Mohit & Verma, S. K. (2022). A Textbook of Plant Physiology, Biochemistry and Biotechnology, S. Chand Publishing. 13th Edition.
5. Lincoln Taiz, Ian Max Møller, Angus Murphy, and Eduardo Zeiger (2022). Plant Physiology and Development, Oxford University Press, 7^th Edition.
6. Nelson, David L. & Cox, Michael M. (2021). Lehninger Principles of Biochemistry, W. H. Freeman, 8^th Edition.

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