Cultivation systems: fed-batch culture MCQs With Answer

Cultivation systems: fed-batch culture MCQs With Answer

This collection of MCQs is designed for M.Pharm students studying Bioprocess Engineering and Technology, focusing on fed-batch cultivation systems. Fed-batch is widely used in pharmaceutical biomanufacturing for recombinant proteins, antibiotics, vaccines and secondary metabolites because it balances high biomass accumulation with controlled nutrient supply to avoid substrate inhibition and by-product formation. These questions cover principles, feeding strategies, kinetics, process control, scale-up challenges, and practical considerations such as oxygen transfer, induction timing, and contamination risks. Use this set to test conceptual understanding, reinforce design choices, and prepare for exams or practical process development decisions in upstream bioprocessing.

Q1. What is the primary objective of using a fed-batch culture instead of a simple batch culture in pharmaceutical fermentations?

• Maintain constant reactor volume while allowing nutrient depletion
• Increase productivity by controlling substrate addition to avoid inhibition and overflow metabolism
• Eliminate the need for aeration and agitation during the run
• Ensure continuous removal of biomass while adding fresh medium

Correct Answer: Increase productivity by controlling substrate addition to avoid inhibition and overflow metabolism

Q2. Which feeding profile is commonly used to maintain a desired specific growth rate (μ) in fed-batch cultures?

• Bolus (pulsed) feeding at irregular intervals
• Constant volumetric feed rate regardless of cell concentration
• Exponential feed profile matched to biomass growth
• Stepwise decreasing feed rate every hour

Correct Answer: Exponential feed profile matched to biomass growth

Q3. In fed-batch operation aimed at maximizing recombinant protein yield with an inducible promoter, what is a key consideration for feed strategy?

• Always feed high carbon to maximize growth before induction
• Delay feeding until after harvest to reduce proteolysis
• Control feed to reach optimal biomass and then induce under nutrient-limited or controlled growth to favor product formation
• Use no induction; rely on constitutive expression only

Correct Answer: Control feed to reach optimal biomass and then induce under nutrient-limited or controlled growth to favor product formation

Q4. Which issue is most associated with excessive glucose feeding in E. coli fed-batch cultures?

• Increased formation of acetate leading to growth inhibition
• Improved oxygen transfer due to higher metabolic rates
• Enhanced plasmid stability and decreased protease expression
• Reduced foam formation and lower viscosity

Correct Answer: Increased formation of acetate leading to growth inhibition

Q5. For a microbial culture following Monod kinetics, how does limiting the substrate feed in fed-batch affect the specific growth rate?

• It forces μ to remain near zero regardless of feed
• It can be used to maintain μ at a set value below μmax by adjusting feed rate
• Specific growth rate becomes independent of substrate concentration
• It always increases μ to μmax because cells receive constant substrate

Correct Answer: It can be used to maintain μ at a set value below μmax by adjusting feed rate

Q6. Which feeding strategy is most appropriate to prevent substrate inhibition when the substrate is toxic at high concentrations?

• Single large bolus at the start of culture
• Constant high-rate feed throughout the run
• Continuous low-rate or pulse feeding to keep substrate below inhibitory threshold
• Adding substrate only at harvest

Correct Answer: Continuous low-rate or pulse feeding to keep substrate below inhibitory threshold

Q7. In fed-batch bioprocess scale-up, which parameter is typically most critical to maintain similar physiological responses between scales?

• Total run time of the fermentation
• Geometric similarity of vessel shape only
• Similarity in volumetric oxygen transfer coefficient (kLa) and mixing time
• Same feed pump brand

Correct Answer: Similarity in volumetric oxygen transfer coefficient (kLa) and mixing time

Q8. What is the principal advantage of exponential feeding compared with constant feeding in fed-batch cultures?

• It reduces the need to monitor biomass concentration
• It maintains a nearly constant specific growth rate throughout the feed phase
• It eliminates the formation of metabolic by-products completely
• It requires no control over feed pump accuracy

Correct Answer: It maintains a nearly constant specific growth rate throughout the feed phase

Q9. Which control variable is most commonly used to implement feedback control for substrate feeding in fed-batch microbial cultures?

• Online biomass optical density (OD) only
• Off-line nutrient assay once per day
• Dissolved oxygen (DO) spike as an indicator of substrate depletion
• Viable cell count every hour

Correct Answer: Dissolved oxygen (DO) spike as an indicator of substrate depletion

Q10. In fed-batch production of secondary metabolites (e.g., antibiotics), which strategy often enhances product formation?

• Maintaining exponential growth at μ ≈ μmax throughout
• Imposing nutrient limitation or stress after sufficient biomass accumulation
• Providing excess carbon and nitrogen to maximize biomass only
• Avoiding any changes in feed composition during run

Correct Answer: Imposing nutrient limitation or stress after sufficient biomass accumulation

Q11. Which of the following describes a major disadvantage of fed-batch compared with continuous culture?

• Fed-batch always yields lower final product concentration
• Process control and feeding complexity are higher in fed-batch
• Fed-batch cannot be run at large industrial scale
• Cells cannot be kept under steady-state conditions in fed-batch

Correct Answer: Process control and feeding complexity are higher in fed-batch

Q12. When designing a feed medium for fed-batch fermentation, why is the carbon to nitrogen (C:N) ratio important?

• C:N ratio only affects pH and not metabolism
• It influences biomass yield, by-product formation and the metabolic state favoring growth versus product formation
• High C:N always prevents contamination
• A fixed C:N is unnecessary because cells synthesize nitrogen de novo

Correct Answer: It influences biomass yield, by-product formation and the metabolic state favoring growth versus product formation

Q13. Which monitoring technique provides the most direct real-time estimate of culture metabolic state for feed control?

• Offline HPLC nutrient analysis every 12 hours
• Online capacitance or dielectric spectroscopy to estimate viable biomass
• Daily microscopic cell counts
• pH measurement only

Correct Answer: Online capacitance or dielectric spectroscopy to estimate viable biomass

Q14. A fed-batch run uses exponential feeding with target μ = 0.2 h−1. If biomass doubles every 3.5 hours approximately, which statement is correct?

• Target μ = 0.2 h−1 corresponds roughly to doubling time of 3.5 hours, so feeding matches growth
• Target μ = 0.2 h−1 implies immediate stationary phase
• Exponential feeding will not affect doubling time
• Doubling time at μ = 0.2 h−1 is closer to 0.5 hours

Correct Answer: Target μ = 0.2 h−1 corresponds roughly to doubling time of 3.5 hours, so feeding matches growth

Q15. Which parameter is a practical indication that the culture has become oxygen-limited during fed-batch growth?

• Stable pO2 at setpoint despite increased agitation
• Sudden rise in dissolved oxygen when feed is increased
• Continuous drop in dissolved oxygen to very low values even after increasing aeration/agitation
• Decrease in off-gas CO2 without changes in substrate feed

Correct Answer: Continuous drop in dissolved oxygen to very low values even after increasing aeration/agitation

Q16. Why is feed sterilization or sterile filtration critical in fed-batch bioprocesses?

• Feeds are sterile by default and need no handling
• Nonsterile feed can introduce contaminants late in the run, compromising product and causing batch loss
• Sterile filtration always removes nutrients harmful to cells
• Feed sterilization reduces osmolarity beneficially

Correct Answer: Nonsterile feed can introduce contaminants late in the run, compromising product and causing batch loss

Q17. In fed-batch culture, what is the common reason to switch from a growth-oriented feed to a production-oriented feed?

• To reduce the need for antifoam agents
• To lower biomass to zero
• To shift metabolism from cell growth to product synthesis (e.g., secondary metabolism or recombinant protein expression)
• To intentionally induce cell death for downstream processing

Correct Answer: To shift metabolism from cell growth to product synthesis (e.g., secondary metabolism or recombinant protein expression)

Q18. Which modeling approach is often used to design and optimize feeding in fed-batch systems?

• Empirical models only with no physiological basis
• Mechanistic models combining Monod-type kinetics, maintenance, yield coefficients and substrate uptake rates
• Using only trial-and-error without models
• Assuming linear growth independent of substrate

Correct Answer: Mechanistic models combining Monod-type kinetics, maintenance, yield coefficients and substrate uptake rates

Q19. What is a key operational difference between fed-batch and perfusion culture strategies?

• Fed-batch continuously removes spent medium while perfusion never removes medium
• Perfusion maintains near-steady-state biomass by continuous medium exchange while fed-batch does not remove culture and accumulates biomass
• Fed-batch uses cell retention devices, perfusion does not
• There is no difference; both are identical in practice

Correct Answer: Perfusion maintains near-steady-state biomass by continuous medium exchange while fed-batch does not remove culture and accumulates biomass

Q20. When planning a fed-batch process for a eukaryotic cell line producing monoclonal antibodies, which consideration is particularly important compared to microbial fed-batch?

• Eukaryotic cells are not sensitive to shear, so agitation can be increased without limit
• Control of shear, osmolality, and complex nutrient feeding (amino acids, lipids) is critical to maintain viability and product quality
• Oxygen transfer is unimportant due to slow metabolic rates
• Rapid exponential feeding to maximize μ is always preferred

Correct Answer: Control of shear, osmolality, and complex nutrient feeding (amino acids, lipids) is critical to maintain viability and product quality

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