Biodegradation of chemicals and industrial waste MCQs With Answer

Introduction: Biodegradation of chemicals and industrial waste is a core topic in Advanced Pharmaceutical Biotechnology for M. Pharm students, focusing on how biological systems transform, detoxify, or mineralize pollutants. This blog provides targeted multiple-choice questions to deepen understanding of microbial pathways, enzymology, environmental factors, and engineering approaches used in treating industrial effluents and hazardous compounds. Questions emphasize mechanisms such as aerobic and anaerobic degradation, cometabolism, plasmid-mediated gene transfer, biosurfactant roles, and reactor design, while also covering monitoring tools and regulatory concerns. Use these MCQs to test conceptual knowledge, apply problem-solving to real-world remediation scenarios, and prepare for advanced examinations and research in environmental biotechnology.

Q1. What best defines ‘biodegradation’ of organic pollutants in environmental biotechnology?

• The chemical hydrolysis of contaminants due to abiotic factors like sunlight
• The enzymatic breakdown of organic pollutants by microorganisms to simpler compounds or mineral end-products
• The physical removal of pollutants by filtration or sedimentation
• The accumulation of contaminants in plant tissues without transformation

Correct Answer: The enzymatic breakdown of organic pollutants by microorganisms to simpler compounds or mineral end-products

Q2. Which factor most often limits the rate of biodegradation of hydrophobic organic chemicals in soil and sludge?

• Ambient pH
• Microbial species diversity
• Bioavailability of the contaminant (mass transfer and sorption)
• Oxygen concentration in the gas phase

Correct Answer: Bioavailability of the contaminant (mass transfer and sorption)

Q3. Compared to anaerobic biodegradation, aerobic biodegradation of organic pollutants generally:

• Produces less energy per mole of substrate oxidized
• Is typically slower and produces more recalcitrant intermediates
• Yields more ATP and often results in faster, more complete mineralization
• Cannot degrade aromatic compounds

Correct Answer: Yields more ATP and often results in faster, more complete mineralization

Q4. What describes ‘cometabolism’ in biodegradation processes?

• Microbial degradation of a pollutant that serves as the sole carbon and energy source for growth
• Simultaneous degradation of two compounds that both serve as primary growth substrates
• Transformation of a non-growth substrate by enzymes produced during metabolism of a separate growth substrate
• Biodegradation that occurs only under anaerobic conditions

Correct Answer: Transformation of a non-growth substrate by enzymes produced during metabolism of a separate growth substrate

Q5. Which enzyme class typically initiates the aerobic biodegradation of polyaromatic hydrocarbons (PAHs) by inserting oxygen into the aromatic ring?

• Hydrolases
• Dehalogenases
• Oxygenases (e.g., dioxygenases and monooxygenases)
• Reductases

Correct Answer: Oxygenases (e.g., dioxygenases and monooxygenases)

Q6. Chlorinated solvents in groundwater are frequently treated biologically by which mechanism under anaerobic conditions?

• Aerobic monooxygenation leading to CO2
• Reductive dechlorination mediated by dehalogenases
• Photolytic cleavage driven by sunlight penetration
• Simple volatilization without transformation

Correct Answer: Reductive dechlorination mediated by dehalogenases

Q7. Which class of PAHs is generally most resistant to microbial biodegradation in soils?

• Low-molecular-weight PAHs (2–3 rings)
• Medium-molecular-weight PAHs (3–4 rings)
• High-molecular-weight PAHs (4 or more fused rings)
• Aliphatic hydrocarbons of similar carbon number

Correct Answer: High-molecular-weight PAHs (4 or more fused rings)

Q8. The typical sequential microbial pathway for complete removal of PCBs in contaminated sediments involves:

• Aerobic oxidation to chlorinated acids followed by photolysis
• Reductive dechlorination under anaerobic conditions followed by aerobic ring cleavage of less-chlorinated congeners
• Direct mineralization under aerobic conditions only
• Volatilization and atmospheric degradation exclusively

Correct Answer: Reductive dechlorination under anaerobic conditions followed by aerobic ring cleavage of less-chlorinated congeners

Q9. What is the primary difference between bioaugmentation and biostimulation as remediation strategies?

• Bioaugmentation adds nutrients; biostimulation adds specialized microbial strains
• Bioaugmentation introduces specialized microbial strains; biostimulation enhances activity of indigenous microbes by adding nutrients or electron acceptors/donors
• They are identical approaches with different names
• Biostimulation always involves genetic engineering of microbes

Correct Answer: Bioaugmentation introduces specialized microbial strains; biostimulation enhances activity of indigenous microbes by adding nutrients or electron acceptors/donors

Q10. Horizontal transfer of catabolic genes that enable pollutant degradation in bacteria is most commonly mediated by:

• Conjugative plasmids and transposons
• Spontaneous chromosomal mutation only
• Vertical inheritance through spores
• Viral infection that always causes cell lysis

Correct Answer: Conjugative plasmids and transposons

Q11. Biosurfactants produced by microbes enhance biodegradation primarily by:

• Inhibiting competing microbial species
• Increasing pollutant solubility and desorption from solids, improving bioavailability
• Acting as terminal electron acceptors
• Directly oxidizing contaminants chemically

Correct Answer: Increasing pollutant solubility and desorption from solids, improving bioavailability

Q12. In constructed wetlands treating industrial wastewater, removal of hydrophobic organic pollutants predominantly occurs by:

• Direct photolysis on the water surface exclusively
• Sorption to sediments and plant roots combined with microbial degradation in biofilms and rhizosphere
• Volatilization only, with no biological transformation
• Immediate chemical oxidation to CO2 without intermediate steps

Correct Answer: Sorption to sediments and plant roots combined with microbial degradation in biofilms and rhizosphere

Q13. Which kinetic model explicitly accounts for microbial growth and substrate saturation in biodegradation?

• Zero-order kinetics
• First-order kinetics
• Monod kinetics
• Michaelis–Menten kinetics applied to abiotic hydrolysis only

Correct Answer: Monod kinetics

Q14. Which statement about heavy metal contamination and biodegradation is correct?

• Heavy metals can be completely biodegraded to CO2 and water by microbes
• Heavy metals cannot be degraded; remediation focuses on immobilization, transformation of speciation, or removal
• All heavy metals are volatile and removed by aeration
• Biodegradation of metals is accelerated by increasing salinity only

Correct Answer: Heavy metals cannot be degraded; remediation focuses on immobilization, transformation of speciation, or removal

Q15. Which monitoring technique measures microbial oxygen consumption to assess biodegradability of a wastewater sample?

• Gas chromatography–mass spectrometry (GC-MS)
• Biochemical oxygen demand (BOD) or respirometry
• Inductively coupled plasma mass spectrometry (ICP-MS)
• pH titration

Correct Answer: Biochemical oxygen demand (BOD) or respirometry

Q16. For treatment of low-solubility, slowly degraded organics where attached growth and long retention improve performance, which reactor type is most suitable?

• Well-mixed suspended-growth batch reactor
• Attached-growth biofilm reactor such as a packed-bed or trickling filter
• Simple sedimentation tank with no biological stage
• Photobioreactor designed for algae only

Correct Answer: Attached-growth biofilm reactor such as a packed-bed or trickling filter

Q17. Laccase enzymes, often used in bioremediation, are most effective at oxidizing which types of pollutants?

• Inorganic anions like nitrate and sulfate
• Phenolic compounds and some recalcitrant aromatic pollutants (via one-electron oxidation)
• Aliphatic hydrocarbons exclusively
• Heavy metals by mineralization

Correct Answer: Phenolic compounds and some recalcitrant aromatic pollutants (via one-electron oxidation)

Q18. Which approach is considered most controversial or restricted when applied in open environmental bioremediation due to ecological and regulatory concerns?

• Biostimulation with added nutrients
• Phytoremediation using native plants
• Release of genetically modified microorganisms (GMOs) engineered to degrade pollutants
• Use of aerobic composting in controlled piles

Correct Answer: Release of genetically modified microorganisms (GMOs) engineered to degrade pollutants

Q19. In assessing persistence of a chemical in the environment, which metric is most directly indicative of its resistance to biodegradation?

• Low octanol–water partition coefficient (Kow)
• Short half-life (DT50)
• High half-life (long DT50)
• High water solubility only

Correct Answer: High half-life (long DT50)

Q20. For monitoring polar, non-volatile transformation products of pharmaceutical contaminants in treatment systems, which analytical technique is most appropriate?

• Gas chromatography–mass spectrometry (GC-MS) without derivatization
• Liquid chromatography–mass spectrometry (LC-MS/MS)
• Flame ionization detection alone
• Gravimetric analysis

Correct Answer: Liquid chromatography–mass spectrometry (LC-MS/MS)

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