Introduction: The properties of secondary metabolites—alkaloids, glycosides, terpenoids and phenolics—govern their bioactivity, extraction, stability and formulation in pharmaceutical applications. For B.Pharm students, mastering physicochemical characteristics (polarity, solubility, pKa, partition coefficient, molecular weight), biosynthetic origins (shikimate, acetate-mevalonate, amino-acid pathways) and analytical identification techniques (HPLC, MS, NMR, UV) is essential to predict bioavailability, metabolism, toxicity and structure–activity relationships. Understanding stability under pH, light and heat, as well as interactions with excipients, aids isolation, standardization and quality control in pharmacognosy and phytopharmaceutical development. Now let’s test your knowledge with 30 MCQs on this topic.
Q1. Which biosynthetic pathway primarily produces aromatic phenolic secondary metabolites?
- Acetate (polyketide) pathway
- Mevalonate pathway
- Shikimate pathway
- Amino acid decarboxylation pathway
Correct Answer: Shikimate pathway
Q2. Which physicochemical property most directly predicts a compound’s membrane permeability?
- Melting point
- Partition coefficient (Log P)
- Optical rotation
- Boiling point
Correct Answer: Partition coefficient (Log P)
Q3. Alkaloids are best defined as secondary metabolites that typically contain which element?
- Nitrogen
- Sulfur
- Phosphorus
- Halogens
Correct Answer: Nitrogen
Q4. Which analytical technique provides definitive molecular weight and fragmentation pattern for secondary metabolites?
- UV-Visible spectroscopy
- Mass spectrometry (MS)
- Infrared spectroscopy (IR)
- Polarimetry
Correct Answer: Mass spectrometry (MS)
Q5. Glycosides are characterized by a sugar moiety attached to an aglycone. Which property of glycosides is most increased by glycosylation?
- Lipophilicity
- Thermal stability
- Water solubility
- UV absorption
Correct Answer: Water solubility
Q6. Which functional group commonly confers antioxidant activity in phenolic secondary metabolites?
- Ether group
- Hydroxyl group on an aromatic ring
- Alkyl halide
- Carboxylate ester
Correct Answer: Hydroxyl group on an aromatic ring
Q7. Which property is most critical when choosing a solvent for extracting non-polar terpenoids from plant material?
- High polarity
- Low boiling point only
- Solvent polarity matching analyte (non-polar)
- Ability to form hydrogen bonds
Correct Answer: Solvent polarity matching analyte (non-polar)
Q8. In stability studies, which condition is most likely to cause hydrolysis of glycosidic bonds in secondary metabolites?
- Neutral pH and darkness
- Acidic pH and elevated temperature
- Low temperature and dry conditions
- Presence of antioxidants
Correct Answer: Acidic pH and elevated temperature
Q9. Which instrument provides information about functional groups present in a secondary metabolite?
- NMR spectroscopy
- Mass spectrometry
- Infrared spectroscopy (IR)
- Microscopy
Correct Answer: Infrared spectroscopy (IR)
Q10. Which class of secondary metabolites is biosynthesized mainly via the mevalonate and non-mevalonate pathways?
- Alkaloids
- Terpenoids (isoprenoids)
- Phenolics
- Glycosides
Correct Answer: Terpenoids (isoprenoids)
Q11. A high polar surface area (PSA) in a secondary metabolite generally predicts which of the following?
- High passive membrane permeability
- Poor aqueous solubility
- Low oral bioavailability due to limited permeation
- Increased volatility
Correct Answer: Low oral bioavailability due to limited permeation
Q12. During HPLC method development for a phenolic compound, which detector is most sensitive to conjugated aromatic systems?
- Evaporative light scattering detector (ELSD)
- PDA/UV-Vis detector
- Refractive index detector
- Flame ionization detector
Correct Answer: PDA/UV-Vis detector
Q13. Which structural feature often increases metabolic stability of a secondary metabolite in the liver?
- Multiple free hydroxyl groups
- Bulky lipophilic substituents near sites of metabolism
- Low molecular weight under 100 Da
- Highly flexible linear chains
Correct Answer: Bulky lipophilic substituents near sites of metabolism
Q14. Which secondary metabolite class commonly shows basic properties and forms salts with acids?
- Flavonoid glycosides
- Alkaloids
- Saponins
- Polyphenols
Correct Answer: Alkaloids
Q15. In TLC profiling of plant extracts, a compound with high Rf on a non-polar solvent system is likely to be:
- Highly polar
- Highly non-polar (lipophilic)
- Highly ionic
- Strongly hydrogen bonded
Correct Answer: Highly non-polar (lipophilic)
Q16. Which property of secondary metabolites is most relevant for predicting skin permeation in topical formulations?
- Color
- Partition coefficient (Log P) and molecular size
- Optical rotation
- Melting point only
Correct Answer: Partition coefficient (Log P) and molecular size
Q17. Which secondary metabolite class is typically amphipathic and can form foam in aqueous solutions?
- Saponins
- Alkaloids
- Terpenes
- Flavones
Correct Answer: Saponins
Q18. Which statement about conjugation (phase II metabolism) of plant secondary metabolites is correct?
- Conjugation generally decreases water solubility
- Glucuronidation increases polarity and renal excretion
- Conjugation always increases pharmacological potency
- Methylation produces large polymers
Correct Answer: Glucuronidation increases polarity and renal excretion
Q19. Which structural analysis technique gives information about hydrogen environments and connectivity in secondary metabolites?
- UV-Vis spectroscopy
- 1H and 13C NMR spectroscopy
- Thin layer chromatography
- Colorimetric assays
Correct Answer: 1H and 13C NMR spectroscopy
Q20. Which property makes phenolic compounds effective free radical scavengers?
- Ability to donate hydrogen/electrons from phenolic OH groups
- High ionic charge
- Low molecular weight alone
- Presence of saturated alkyl chains
Correct Answer: Ability to donate hydrogen/electrons from phenolic OH groups
Q21. During isolation, which technique separates compounds based on polarity differences using a polar stationary phase?
- Normal-phase chromatography
- Size-exclusion chromatography
- Reverse-phase chromatography
- Gas chromatography
Correct Answer: Reverse-phase chromatography
Q22. Which property of a secondary metabolite most influences its volatilization and suitability for GC analysis?
- Thermal stability and volatility (low boiling point)
- High molecular polarity
- Ability to form salts
- High molecular mass (>1000 Da)
Correct Answer: Thermal stability and volatility (low boiling point)
Q23. Which parameter measured by HPLC is most useful for quantifying a known secondary metabolite in a sample?
- Retention time alone
- Peak area against a calibration curve
- Color of the eluent
- pH of mobile phase only
Correct Answer: Peak area against a calibration curve
Q24. Which chemical modification commonly increases lipophilicity and membrane permeability of a polar secondary metabolite?
- Glycosylation
- Methylation or esterification of hydroxyl groups
- Hydroxylation
- Sulfation
Correct Answer: Methylation or esterification of hydroxyl groups
Q25. In chemotaxonomy, which concept is applied when certain secondary metabolites are characteristic markers for specific plant taxa?
- Random distribution principle
- Species-specific biosynthetic pathways producing marker compounds
- Universal secondary metabolite profile across all plants
- Metabolite instability excludes taxonomic use
Correct Answer: Species-specific biosynthetic pathways producing marker compounds
Q26. Which property is most likely to cause degradation of light-sensitive flavonoids during storage?
- Storage at low humidity in amber bottles
- Exposure to ultraviolet and visible light
- Storage at sub-zero temperatures
- Presence of desiccants
Correct Answer: Exposure to ultraviolet and visible light
Q27. Which extraction method is most suitable for heat-sensitive polyphenols to minimize degradation?
- Reflux extraction at high temperature for long time
- Cold maceration or ultrasound-assisted extraction at controlled low temperature
- Dry distillation
- Boiling in strong acid
Correct Answer: Cold maceration or ultrasound-assisted extraction at controlled low temperature
Q28. Structure–activity relationship (SAR) studies of alkaloids focus on which aspects to optimize pharmacological effect?
- Only molecular weight
- Functional group modifications and stereochemistry
- Color and odor changes
- Source plant species only
Correct Answer: Functional group modifications and stereochemistry
Q29. Which property is directly assessed by measuring pKa of a secondary metabolite?
- Optical activity
- Degree of ionization at a given pH
- Molecular weight
- Thermal decomposition point
Correct Answer: Degree of ionization at a given pH
Q30. For formulation of a poorly water-soluble terpenoid, which strategy is commonly used to enhance oral bioavailability?
- Formulate as a simple aqueous solution without solubilizers
- Use lipid-based delivery systems, nanoemulsions or cyclodextrin complexation
- Increase particle size to >1 mm
- Add strong acids to degrade the terpenoid
Correct Answer: Use lipid-based delivery systems, nanoemulsions or cyclodextrin complexation
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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