Biodegradation of xenobiotics MCQs With Answer

Biodegradation of xenobiotics MCQs With Answer

by

Introduction: Biodegradation of xenobiotics MCQs With Answer is designed for M.Pharm students specializing in Advanced Pharmaceutical Biotechnology. This collection focuses on microbial and enzymatic processes that transform synthetic and recalcitrant chemical pollutants (xenobiotics) in environmental and clinical contexts. Questions cover mechanisms of biotransformation, key enzyme systems (e.g., monooxygenases, dioxygenases, dehalogenases), cometabolism, factors influencing degradation rates, metabolic pathways for persistent pollutants (PAHs, chlorinated solvents, pesticides), and practical bioremediation strategies such as bioaugmentation and biostimulation. Each MCQ aims to strengthen conceptual understanding, application of principles, and interpretation of experimental approaches used to study and enhance xenobiotic biodegradation.

Q1. What is the primary distinction between biodegradation and biotransformation of xenobiotics?

  • Biodegradation implies complete mineralization to CO2 and H2O, while biotransformation denotes any enzymatic modification including partial transformation
  • Biodegradation always requires aerobic conditions, whereas biotransformation is strictly anaerobic
  • Biodegradation refers only to fungal activity, and biotransformation refers only to bacterial activity
  • Biodegradation is a chemical process, while biotransformation is a physical separation technique

Correct Answer: Biodegradation implies complete mineralization to CO2 and H2O, while biotransformation denotes any enzymatic modification including partial transformation

Q2. Which enzyme class is most commonly involved in the initial oxidative attack on polycyclic aromatic hydrocarbons (PAHs)?

  • Dehydrogenases
  • Ring-cleaving hydrolases
  • Monooxygenases and dioxygenases
  • Reductases

Correct Answer: Monooxygenases and dioxygenases

Q3. Cometabolism in xenobiotic degradation refers to:

  • Microbial degradation of a compound when it is used as the sole carbon and energy source
  • Enzymatic transformation of a xenobiotic that occurs incidentally during metabolism of a primary substrate
  • Abiotic chemical breakdown mediated by sunlight
  • Physical removal of xenobiotics by adsorption onto biomass

Correct Answer: Enzymatic transformation of a xenobiotic that occurs incidentally during metabolism of a primary substrate

Q4. Which factor generally decreases the biodegradation rate of hydrophobic organic xenobiotics in soils?

  • High soil organic carbon content leading to strong sorption
  • Optimal temperature and moisture for microbial activity
  • Presence of a diverse microbial community with degradative genes
  • Bioavailability enhanced by biosurfactants

Correct Answer: High soil organic carbon content leading to strong sorption

Q5. Reductive dehalogenation is a key anaerobic process for detoxifying which class of compounds?

  • Simple sugars and amino acids
  • Chlorinated solvents such as trichloroethene (TCE)
  • Non-halogenated hydrocarbons like benzene
  • Heavy metals like lead and cadmium

Correct Answer: Chlorinated solvents such as trichloroethene (TCE)

Q6. Plasmid-borne catabolic genes important for xenobiotic degradation are often transferred between bacteria by:

  • Binary fission
  • Conjugation
  • Transduction by bacteriophages only
  • Absorption through passive diffusion

Correct Answer: Conjugation

Q7. Which analytical technique is most appropriate for identifying polar metabolites formed during xenobiotic biodegradation?

  • Gas chromatography with flame ionization detector (GC-FID) without derivatization
  • High-performance liquid chromatography coupled with mass spectrometry (HPLC-MS)
  • Atomic absorption spectroscopy (AAS)
  • Nuclear magnetic resonance applied to untreated solid samples only

Correct Answer: High-performance liquid chromatography coupled with mass spectrometry (HPLC-MS)

Q8. In microbial degradation kinetics, the Monod model relates specific growth rate to which factor?

  • Temperature only
  • Concentration of substrate (limiting nutrient)
  • Electrochemical potential of the medium
  • Population genetic diversity

Correct Answer: Concentration of substrate (limiting nutrient)

Q9. Which microbial strategy is described by introducing specialized degraders into a contaminated site?

  • Biostimulation
  • Bioaugmentation
  • Phytoremediation
  • Natural attenuation

Correct Answer: Bioaugmentation

Q10. Which compound is known to act as a common cometabolic co-substrate that stimulates oxygenase-mediated degradation of xenobiotics?

  • Glucose exclusively via glycolysis
  • Simple alcohols such as methanol or ethanol
  • Heavy metal salts
  • Polychlorinated biphenyls (PCBs) as sole nutrients

Correct Answer: Simple alcohols such as methanol or ethanol

Q11. Which molecular technique is most suitable for detecting functional genes encoding dehalogenases in environmental samples?

  • 16S rRNA sequencing only
  • Quantitative PCR (qPCR) targeting specific functional genes
  • Protein gel electrophoresis without identification
  • Total organic carbon analysis

Correct Answer: Quantitative PCR (qPCR) targeting specific functional genes

Q12. Which statement about surfactants and biodegradation of hydrophobic xenobiotics is correct?

  • All synthetic surfactants always increase biodegradation by dissolving contaminants
  • Biosurfactants can enhance bioavailability and thus may increase biodegradation rates
  • Surfactants permanently immobilize contaminants and prevent degradation
  • Surfactants are toxic to microbes and invariably inhibit degradation

Correct Answer: Biosurfactants can enhance bioavailability and thus may increase biodegradation rates

Q13. Metabolic pathway reconstruction for a xenobiotic typically requires which combination of data?

  • Only pH and temperature measurements
  • Identification of metabolites, enzyme activities, and gene expression data
  • Counting colony forming units without chemical analysis
  • Visual observation of color change in soil samples only

Correct Answer: Identification of metabolites, enzyme activities, and gene expression data

Q14. Which class of enzymes catalyzes ring cleavage of aromatic compounds after initial hydroxylation?

  • Peroxidases that only oxidize metals
  • Aryl alcohol dehydrogenases exclusively
  • Ring‑cleaving dioxygenases (intradiol or extradiol)
  • Proteases that degrade proteins

Correct Answer: Ring‑cleaving dioxygenases (intradiol or extradiol)

Q15. In aerobic bioreactors treating xenobiotic-contaminated water, which parameter is most critical to maintain high degradation rates?

  • Excessive salinity above microbial tolerance
  • Adequate dissolved oxygen concentration
  • Complete sterilization to prevent contamination
  • Absence of any carbon source besides the xenobiotic

Correct Answer: Adequate dissolved oxygen concentration

Q16. Which of the following is a common limitation when applying bioaugmentation in the field?

  • Introduced strains always outcompete native microbes easily
  • Poor survival and activity of the introduced strains due to predation, competition, or environmental stress
  • Instant and permanent removal of all contaminants
  • Bioaugmentation eliminates the need for monitoring

Correct Answer: Poor survival and activity of the introduced strains due to predation, competition, or environmental stress

Q17. Which metabolic phase in pharmaceutical xenobiotic processing typically introduces polar functional groups making molecules more water soluble?

  • Phase I (functionalization reactions)
  • Phase III (excretion transporters)
  • Abiotic photolysis only
  • Phase IV (polymerization)

Correct Answer: Phase I (functionalization reactions)

Q18. Which microbial guild is particularly important for anaerobic mineralization of aromatics under sulfate‑reducing conditions?

  • Obligate aerobic nitrifiers
  • Sulfate-reducing bacteria capable of activating aromatics via addition reactions
  • Photosynthetic algae only
  • Archaeal methanogens exclusively

Correct Answer: Sulfate-reducing bacteria capable of activating aromatics via addition reactions

Q19. Which approach uses plants to enhance microbial degradation of xenobiotics in the rhizosphere?

  • Phytoremediation with rhizodegradation
  • Ion exchange filtration
  • Chemical oxidation in situ
  • Thermal desorption

Correct Answer: Phytoremediation with rhizodegradation

Q20. Metagenomic sequencing of a contaminated site primarily helps to:

  • Directly measure the concentration of xenobiotics without sample processing
  • Reveal the genetic potential of the microbial community for xenobiotic degradation
  • Sterilize the sample to remove microbial DNA
  • Only quantify heavy metals present in the environment

Correct Answer: Reveal the genetic potential of the microbial community for xenobiotic degradation

Leave a Comment