COMPETITIVE EXAM MCQs SERIES of LIFE SCIENCES for CSIR-UGC NET/JRF, SLET, GATE, and other entrance tests: PLANT PHYSIOLOGY – Secondary Metabolites in Plants and Their Role.
Syllabus Outline
- Types and classes of secondary metabolites in plants
- Biosynthesis of terpenes, phenolic and nitrogenous compounds.
- Physiological roles of secondary metabolites and their ecological significance.
- Regulation and Localisation – gene expression, tissue-specific accumulation, and transport of secondary metabolites.
- Biotechnological and industrial applications of secondary metabolites.
This quiz contains 25 concept-based, most frequently asked MCQs on “PLANT PHYSIOLOGY – Secondary Metabolites in Plants and Their Role”. Each question has a single correct/most appropriate answer.
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1. Which specific environmental stress is primarily mitigated by the accumulation of phenylpropanoid compounds in epidermal layers?
A) Drought stress via osmotic regulation
B) Heavy metal toxicity via chelation
C) Fungal infection via antimicrobial action
D) Ultraviolet radiation damage
2. Which key feature classifies secondary metabolites distinctly from primary metabolites of plants?
A) They are synthesised in the chloroplasts and stored in vacuoles
B) They are structurally characterised by having a heterocyclic ring.
C) They are not essential for cell structure or basic growth processes.
D) They are regulated by phytohormone.
3. The shikimate pathway begins with the condensation of which two substrates?
A) Acetyl-CoA and glyoxylate
B) Phosphoenolpyruvate and erythrose-4-phosphate
C) Pyruvate and glyceraldehyde-3-phosphate
D) Succinyl-CoA and glycine
4. Glyphosate, a widely used herbicide, inhibits which enzyme in the shikimate pathway?
A) Shikimate kinase
B) 3-Dehydroquinate synthase
C) 5-Enolpyruvylshikimate-3-phosphate synthase
D) Chorismate synthase
5. When the enzyme 5-enolpyruvylshikimate-3-phosphate synthase is inhibited by glyphosate, what major metabolic effect occurs in plant cells?
A) Accumulation of chorismate
B) Depletion of shikimate-3-phosphate
C) Accumulation of shikimate
D) Conversion of shikimate into sucrose
6. Phenylalanine ammonia-lyase catalyses the first step in the phenylpropanoid pathway. What product is formed in this reaction?
A) Chorismic acid
B) Cinnamic acid
C) Shikimic acid
D) p-Coumaroyl-CoA
7. Which amino acids provide the nitrogen skeleton for the biosynthesis of tropane alkaloids in plants such as Datura and Atropa?
A) Tryptophan and phenylalanine
B) Ornithine and arginine
C) Lysine and histidine
D) Methionine and cysteine
8. Long-term detoxification of cyanide in animals and plants depends on which nutritional components?
A) Vitamin B₁₂ and folate
B) Sulfur-containing amino acids
C) NADPH oxidase enzymes
D) β-glycosidase enzymes
9. The occurrence of alkaloid biosynthetic steps in multiple cellular compartments provides what main advantage to the plant?
A) It increases the maximum enzyme activity.
B) It prevents the accumulation of intermediates in the endoplasmic reticulum.
C) It reduces cellular toxicity and enhances metabolic efficiency.
D) It increases the number of gene copies encoding the enzymes.
10. Catechins and other phenolic compounds released by certain invasive plants act as allelochemicals. How do these compounds promote invasion success?
A) They change the soil pH.
B) They inhibit the growth of mycorrhizal fungi.
C) They inhibit flowering in native species.
D) They inhibit nitrogen fixation in the soil.
11. What is the main ecological advantage of tissue-specific accumulation of defensive secondary metabolites in plants?
A) It minimises metabolic cost.
B) It protects against tissue-specific attackers.
C) It facilitates tissue-specific systemic signalling.
D) It promotes the degradation of toxins.
12. A deficiency of lignin biosynthesis in plants leads primarily to which physiological defect?
A) Increased sensitivity to ultraviolet light
B) Weak secondary cell walls and collapse of vascular tissues
C) Loss of floral fragrance production
D) Depletion of aromatic amino acids
13. Compounds such as piperine and berberine that accumulate in seeds and roots function mainly to:
A) Enhance nutrient absorption
B) Signal beneficial microorganisms
C) Defend against soil-borne pathogens
D) Regulate transpiration rate
14. Multidrug and toxic compound extrusion transporters mediate the vacuolar transport of flavonoid conjugates, by which driving force?
A) Hydrolysis of adenosine triphosphate
B) Sodium–potassium co-transport
C) Proton antiport mechanism
D) Passive diffusion through the membrane
15. If the vacuolar proton gradient is disrupted in a plant cell, how will this affect the function of Multidrug and toxic compound extrusion transporters?
A) The transporters will change their substrate specificity.
B) The transporters will cease to function due to loss of proton motive force.
C) The transporters will switch to ATP hydrolysis for energy.
D) The rate of substrate accumulation will increase.
16. What is the main functional advantage of metabolic channelling within multienzyme complexes in plant secondary metabolism?
A) Recycling of precursors
B) Protection of unstable intermediates
C) Enhancement of feedback inhibition
D) Regulation of water potential
17. Why do many alkaloid biosynthetic pathways in plants involve multienzyme complexes?
A) To prevent product degradation
B) To maximise metabolic flux toward the final product efficiently
C) To reduce the energetic cost of protein synthesis
D) To promote intermediate breakdown
18. Which of the following factors collectively regulate the accumulation of defence-related secondary metabolites in plants?
I – Stress-induced transcription factors
II – MicroRNAs
III – Vacuolar transporters
IV – Exogenous elicitors
A) I and III
B) I, II, and IV
C) II, III, and IV
D) I, II, III, and IV
19. The biosynthesis of major classes of secondary metabolites relies on distinct metabolic precursors and fundamental building blocks. Consider the following pairs linking the metabolite class to its primary chemical precursor and basic structural unit:
I – Terpenoids: Acetyl-CoA → Five-carbon isoprene unit
II – Phenolics: Shikimate Pathway → Phenylpropanoid unit
III – Alkaloids: Various Amino Acids → Heterocyclic nitrogen-containing ring
IV – Polyketides: Malonyl-CoA → Acetyl units
Which of the pairs correctly describe the biosynthetic origin of plant secondary metabolites?
A) I, II, and III only
B) II, III, and IV only
C) I, II, III, and IV
D) I and IV only
20. A mutant plant lacking the bifunctional enzyme 3-dehydroquinate dehydratase and shikimate dehydrogenase will most likely exhibit which features?
I – Reduced levels of lignin and flavonoids
II – Accumulation of 3-dehydroquinate
III – Normal synthesis of monoterpenes
IV – Increased flux through the mevalonate pathway
A) I and III
B) I, II, and IV
C) II and III
D) I, II, and III
21. Assertion (A): Certain invasive plants gain a competitive advantage through allelopathy.
Reason (R): Their allelochemicals inhibit the growth of native mycorrhizal fungi and reduce nutrient uptake by neighbouring plants.
A) Both A and R are true, and R explains A.
B) Both A and R are true, but R does not explain A.
C) A is true, but R is false.
D) A is false, but R is true.
22. Assertion (A): Channelling of metabolic intermediates between enzymes in plant secondary metabolism enhances efficiency.
Reason (R): Metabolic channelling reduces diffusion loss and protects unstable intermediates from degradation.
A) Both A and R are true, and R explains A.
B) Both A and R are true, but R does not explain A.
C) A is true, but R is false.
D) A is false, but R is true.
23. Assertion (A): Many terpenoids, such as limonene and oleanolic acid, exhibit potent antimicrobial activity against bacteria.
Reason (R): The primary physiological function of these terpenoids is to act as constitutive defences, offering protection to the plant against pathogens.
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.
24. Assertion (A): In higher plants, each of the seven reactions of the shikimate pathway is catalysed by a separate enzyme.
Reason (R): In fungi, a single multifunctional enzyme complex called the AROM complex catalyses five consecutive reactions of the same pathway.
A) Both A and R are true, and R explains A.
B) Both A and R are true, but R does not explain A.
C) A is true, but R is false.
D) A is false, but R is true.
25. Assertion (A): Allelochemicals are toxic to all nearby plants.
Reason (R): Allelopathic effects are specific to certain species and depend on the nature of the compound.
A) Both A and R are true, and R explains A.
B) Both A and R are true, but R does not explain 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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