Basic principles of fermentation MCQs With Answer

Introduction: Basic Principles of Fermentation MCQs With Answer is designed for M.Pharm students to reinforce core bioprocess concepts critical for pharmaceutical biotechnology. The set focuses on microbial growth kinetics, reactor types, oxygen transfer, sterility, inoculum development, and primary versus secondary metabolite production — topics commonly encountered in biopharmaceutical development and quality control. Each question targets analytical understanding and application of principles such as Monod kinetics, yield and maintenance energy, aeration/agitation effects (kLa, OUR), and operational modes (batch, fed-batch, continuous). This concise, practice-oriented quiz helps students prepare for exams and practical problem-solving in formulation, upstream process design, and regulatory expectations.

Q1. What phase of microbial growth is characterized by adaptation to new environment with little or no cell division but high metabolic activity?

• Lag phase
• Log (exponential) phase
• Stationary phase
• Death phase

Correct Answer: Lag phase

Q2. Which parameter in the Monod equation (μ = μmax·S/(Ks+S)) represents the substrate concentration at which the specific growth rate is half of μmax?

• μmax
• Ks
• Yx/s (yield coefficient)
• kLa (volumetric mass transfer coefficient)

Correct Answer: Ks

Q3. In a stirred-tank aerobic fermenter, which factor primarily determines oxygen transfer rate (OTR) to the culture?

• Substrate concentration only
• Volumetric mass transfer coefficient (kLa) and dissolved oxygen driving force
• Inoculum age
• pH of the medium only

Correct Answer: Volumetric mass transfer coefficient (kLa) and dissolved oxygen driving force

Q4. Which operational mode maintains a constant culture volume and allows steady-state continuous supply of fresh medium and removal of culture?

• Batch fermentation
• Fed-batch fermentation
• Continuous (chemostat) fermentation
• Solid-state fermentation

Correct Answer: Continuous (chemostat) fermentation

Q5. Which of the following best describes the yield coefficient Yx/s?

• Rate of substrate consumption per unit volume
• Biomass produced per unit substrate consumed
• Maintenance energy required per cell
• Maximum specific growth rate

Correct Answer: Biomass produced per unit substrate consumed

Q6. Secondary metabolites are usually produced during which phase of growth?

• Exponential (log) phase
• Lag phase
• Stationary phase
• Initial inoculation phase

Correct Answer: Stationary phase

Q7. In sterilization validation of liquid media, what does the F-value quantify?

• The flow rate of steam into autoclave
• Time required at a specified temperature to achieve a certain log reduction of a target microorganism
• The final concentration of nutrients after sterilization
• The pH change caused by sterilization

Correct Answer: Time required at a specified temperature to achieve a certain log reduction of a target microorganism

Q8. Which variable is most commonly controlled to prevent foam-related issues in aerobic fermentations?

• pH using acid/base
• Antifoam addition and controlled agitation/airflow
• Substrate feeding frequency
• Temperature cycling

Correct Answer: Antifoam addition and controlled agitation/airflow

Q9. The term “maintenance energy” in microbial kinetics refers to:

• Energy used only for biomass synthesis
• Energy required to maintain cell viability without growth
• Energy lost as heat to the environment
• Additional ATP used for product formation

Correct Answer: Energy required to maintain cell viability without growth

Q10. In a chemostat, increasing the dilution rate (D) above a critical value will most likely cause:

• Higher biomass concentration indefinitely
• Washout of microorganisms when D exceeds μmax
• Complete conversion of substrate to product
• Switch from aerobic to anaerobic metabolism

Correct Answer: Washout of microorganisms when D exceeds μmax

Q11. Which measurement directly indicates oxygen uptake by the culture?

• OUR (oxygen uptake rate)
• kLa value
• Dissolved CO2 concentration
• pH

Correct Answer: OUR (oxygen uptake rate)

Q12. For fed-batch processes aimed at preventing overflow metabolism (e.g., acetate formation in E. coli), the feeding strategy primarily controls:

• Dissolved oxygen tension only
• Specific substrate uptake rate and growth rate
• Sterility of the fermenter
• Cell death rate exclusively

Correct Answer: Specific substrate uptake rate and growth rate

Q13. Which reactor parameter is increased to enhance mixing and oxygen transfer but may also increase shear stress on cells?

• Decrease in temperature
• Increase in agitation speed
• Lowering pH
• Reducing medium viscosity

Correct Answer: Increase in agitation speed

Q14. Which statement about sterilization by moist heat (autoclaving) is correct?

• Dry heat is more effective than moist heat at lower temperatures
• Moist heat kills microbes largely by protein denaturation and is faster than dry heat at equivalent temperatures
• Autoclaving cannot inactivate bacterial spores
• Sterilization time decreases with decreasing load and increasing humidity only

Correct Answer: Moist heat kills microbes largely by protein denaturation and is faster than dry heat at equivalent temperatures

Q15. Which factor most strongly influences the oxygen solubility in the fermentation broth?

• Agitation impeller type only
• Temperature and salt concentration (medium composition)
• pH alone
• Inoculum size only

Correct Answer: Temperature and salt concentration (medium composition)

Q16. The specific growth rate μ can be experimentally determined from which plot?

• Plot of pH versus time
• Exponential slope of ln(biomass concentration) versus time
• Substrate concentration versus agitation speed
• Temperature profile over time

Correct Answer: Exponential slope of ln(biomass concentration) versus time

Q17. Which is a principal advantage of fed-batch fermentation for recombinant protein production?

• Constant environment with no nutrient gradients forever
• Ability to control growth rate and substrate concentration to reduce byproduct formation and proteolysis
• Always higher kLa than continuous reactors
• No need for sterilization steps

Correct Answer: Ability to control growth rate and substrate concentration to reduce byproduct formation and proteolysis

Q18. Which microbial cultivation method is most appropriate when product formation is growth-associated and high cell density is desired?

• Batch culture only
• Continuous chemostat at very low dilution rates
• Fed-batch to achieve high cell density while controlling substrate
• Solid-state fermentation exclusively

Correct Answer: Fed-batch to achieve high cell density while controlling substrate

Q19. Which of the following best describes kLa in bioreactors?

• Equilibrium concentration of oxygen in liquid
• Product formation rate constant
• Volumetric mass transfer coefficient combining interfacial area (a) and mass transfer coefficient (kL)
• Rate of thermal conduction through reactor wall

Correct Answer: Volumetric mass transfer coefficient combining interfacial area (a) and mass transfer coefficient (kL)

Q20. When designing inoculum development for an industrial fermentation, which practice is most important to ensure reproducibility at scale?

• Using an arbitrarily high inoculum volume to shorten lag phase
• Stepwise scale-up of seed cultures under the same medium and physiologic conditions as the production fermenter
• Omitting sterility checks to save time
• Switching carbon sources at the last seed stage to boost growth

Correct Answer: Stepwise scale-up of seed cultures under the same medium and physiologic conditions as the production fermenter

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