Introduction
Design and operation of bioreactors MCQs With Answer is a focussed quiz collection tailored for M.Pharm students specializing in bioprocess engineering and biotechnology. This set emphasizes core principles such as reactor types (stirred tanks, airlifts, bubble columns), mass and heat transfer, oxygen transfer (kLa, OTR, OUR), mixing, scale‑up criteria, agitation and sparging design, shear effects, sterilization, control strategies, and single‑use systems. Each question challenges conceptual understanding and application of quantitative and design considerations encountered in laboratory and industrial bioprocesses. Use these MCQs to review critical topics, identify knowledge gaps, and prepare for exams and practical design tasks in bioreactor engineering.
Q1. What is the primary function of a bioreactor in pharmaceutical bioprocessing?
- To provide a sterile, controlled environment for biological growth and product formation
- To chemically synthesize active pharmaceutical ingredients without living cells
- To separate cellular components by centrifugation
- To package final drug products under aseptic conditions
Correct Answer: To provide a sterile, controlled environment for biological growth and product formation
Q2. What does the volumetric oxygen transfer coefficient (kLa) represent in aerobic bioprocesses?
- The volumetric mass transfer coefficient for oxygen from gas phase to liquid phase
- The maximum oxygen concentration that cells can tolerate
- The oxygen uptake rate per unit biomass
- The ratio of gas flow rate to liquid volume
Correct Answer: The volumetric mass transfer coefficient for oxygen from gas phase to liquid phase
Q3. Which bioreactor type is most commonly used for heterogeneous microbial aerobic fermentations because of its mixing and oxygen transfer performance?
- Stirred tank reactor (STR)
- Packed bed reactor
- Fixed‑film reactor
- Membrane bioreactor
Correct Answer: Stirred tank reactor (STR)
Q4. Which scale‑up criterion is often used to maintain similar mixing intensity and oxygen transfer when scaling microbial stirred tanks?
- Constant power input per unit volume (P/V)
- Constant vessel diameter
- Constant gas superficial velocity
- Constant impeller blade thickness
Correct Answer: Constant power input per unit volume (P/V)
Q5. The Rushton turbine impeller is primarily characterized as which type and is best suited for what purpose?
- Radial‑flow turbine suited for gas dispersion and high shear mixing
- Axial‑flow impeller suited for gentle circulation of shear‑sensitive cells
- Propeller impeller suited for low oxygen transfer applications
- Pitched‑blade turbine suited for laminar flow systems only
Correct Answer: Radial‑flow turbine suited for gas dispersion and high shear mixing
Q6. Which sparger design typically produces the smallest bubble size and highest interfacial area for oxygen transfer?
- Porous (sintered) sparger
- Single large orifice sparger
- Annular ring sparger with large holes
- External venturi sparger without jets
Correct Answer: Porous (sintered) sparger
Q7. How is the oxygen uptake rate (OUR) of a culture defined in bioreactor operation?
- The rate of oxygen consumption by the culture per unit reactor volume
- The maximum oxygen transfer capacity of the sparger
- The amount of oxygen dissolved in the medium at saturation
- The gas flow rate required to avoid oxygen limitation
Correct Answer: The rate of oxygen consumption by the culture per unit reactor volume
Q8. What is meant by the term ‘critical dissolved oxygen concentration’ in aerobic cultures?
- The dissolved oxygen level below which the specific growth rate becomes oxygen‑limited
- The maximum dissolved oxygen concentration cells can tolerate
- The dissolved oxygen concentration at which bubbles coalesce rapidly
- The oxygen level required for foaming to start
Correct Answer: The dissolved oxygen level below which the specific growth rate becomes oxygen‑limited
Q9. Typical sterilization‑in‑place (SIP) conditions for stainless steel bioreactors to achieve commercial sterility are commonly:
- 121 °C for 20–30 minutes at saturated steam conditions
- 80 °C for 2 hours without steam
- 60 °C for 10 minutes with circulating ethylene oxide
- 200 °C dry heat for 5 minutes
Correct Answer: 121 °C for 20–30 minutes at saturated steam conditions
Q10. What is a common effect of adding silicone antifoam to an aerobic culture?
- Reduction of foam formation but potential decrease in volumetric oxygen transfer (kLa)
- Increase in kLa and improved oxygen transfer
- Immediate sterilization of the medium
- Complete elimination of dissolved oxygen
Correct Answer: Reduction of foam formation but potential decrease in volumetric oxygen transfer (kLa)
Q11. Which reactor exhibits the broadest residence time distribution (RTD), often leading to backmixing?
- Continuous stirred tank reactor (CSTR)
- Plug flow reactor (PFR)
- Packed bed reactor under ideal plug flow
- Ideal tubular reactor with no dispersion
Correct Answer: Continuous stirred tank reactor (CSTR)
Q12. The power number (Np) for an impeller is a dimensionless parameter defined as which ratio?
- P/(ρ N^3 D^5), relating power draw to fluid density, speed and impeller size
- Re/(Fr Np), relating Reynolds to Froude numbers
- kLa divided by the gas flow rate
- Tip speed divided by impeller diameter
Correct Answer: P/(ρ N^3 D^5), relating power draw to fluid density, speed and impeller size
Q13. What is a principal advantage of single‑use (disposable) bioreactors in pharmaceutical production?
- Reduced cleaning/sterilization requirements and lower cross‑contamination risk
- Unlimited scalability without change in hydrodynamics
- Superior heat transfer compared to stainless steel at large scale
- Ability to operate at extreme pressures and temperatures
Correct Answer: Reduced cleaning/sterilization requirements and lower cross‑contamination risk
Q14. For highly exothermic fermentations, which heat removal strategy is generally most effective at large scale?
- Combination of external jacket and internal coils or high‑efficiency heat exchangers to increase heat transfer area
- Relying solely on ambient air cooling without jackets
- Insulating the vessel to prevent heat loss
- Adding cold saline directly to the culture as primary cooling
Correct Answer: Combination of external jacket and internal coils or high‑efficiency heat exchangers to increase heat transfer area
Q15. Which impeller style is recommended for shear‑sensitive mammalian cell cultures to minimize cell damage?
- Low‑shear axial‑flow impeller (e.g., marine propeller or pitched‑blade)
- High‑shear Rushton turbine
- Disc turbine with serrated edges
- High speed rotor‑stator mixer
Correct Answer: Low‑shear axial‑flow impeller (e.g., marine propeller or pitched‑blade)
Q16. To maintain strict anaerobic conditions in a bioreactor you would typically:
- Sparge and blanket the reactor with inert gas (e.g., N2 or CO2) and avoid oxygen ingress
- Continuously sparge with air at high flow rates
- Keep the reactor open to atmosphere and stir vigorously
- Use pure oxygen sparging to overwhelm anaerobes
Correct Answer: Sparge and blanket the reactor with inert gas (e.g., N2 or CO2) and avoid oxygen ingress
Q17. What are the SI units of the volumetric mass transfer coefficient kLa commonly reported as?
- s‑1 (reciprocal seconds), i.e., time‑1
- kg m‑3
- moles per liter
- m s‑1 (velocity)
Correct Answer: s‑1 (reciprocal seconds), i.e., time‑1
Q18. Which scale‑up strategy is often chosen to protect shear‑sensitive cultures (e.g., mammalian) when moving from bench to production scale?
- Maintain constant impeller tip speed to keep shear levels similar
- Maintain constant gas superficial velocity regardless of scale
- Keep constant vessel aspect ratio without adjusting agitation
- Increase impeller speed proportionally to vessel volume
Correct Answer: Maintain constant impeller tip speed to keep shear levels similar
Q19. The oxygen transfer rate (OTR) from gas to liquid at any moment can be expressed by which equation?
- OTR = kLa (C* – CL)
- OTR = P/V × Np
- OTR = μmax × X
- OTR = F/V where F is feed flow rate
Correct Answer: OTR = kLa (C* – CL)
Q20. For a continuous stirred tank reactor (CSTR) operating at steady state, the mean residence time (τ) equals which expression?
- V/F (reactor working volume divided by volumetric effluent flow rate)
- F/V (volumetric flow rate divided by volume)
- Np × ρ (power number times density)
- kLa × (C* – CL)
Correct Answer: V/F (reactor working volume divided by volumetric effluent flow rate)
