Cultivation systems: batch culture MCQs With Answer
Cultivation systems, especially batch culture, form a core part of bioprocess engineering for M.Pharm students involved in pharmaceutical biotechnology. This set of MCQs explores fundamental and applied aspects of batch culture: growth phases, Monod kinetics, substrate limitation and inhibition, yield and maintenance coefficients, oxygen transfer limits, measurement techniques, and implications for product formation and scale-up. Questions are designed to test conceptual understanding and problem-solving ability relevant to lab practice and process design. Correct answers are provided to reinforce learning and help students prepare for exams and practical applications in biopharmaceutical production and upstream process optimization.
Q1. Which phase of a batch culture is characterized by cellular adaptation to the new environment with little or no net increase in biomass?
- Exponential (log) phase
- Stationary phase
- Lag phase
- Death phase
Correct Answer: Lag phase
Q2. In Monod kinetics, the specific growth rate μ = μmax * S / (Ks + S). What does Ks represent biologically?
- The substrate concentration at which μ is half of μmax
- The maximum specific growth rate
- The substrate concentration at zero growth
- The yield coefficient of biomass on substrate
Correct Answer: The substrate concentration at which μ is half of μmax
Q3. Which of the following best describes a growth-associated product in batch culture?
- Product formation occurs mainly during stationary phase
- Product formation rate is proportional to the specific growth rate
- Product is formed after cell lysis
- Product formation is independent of growth rate
Correct Answer: Product formation rate is proportional to the specific growth rate
Q4. Which parameter quantifies the amount of biomass produced per unit substrate consumed?
- Specific growth rate (μ)
- Yield coefficient (Yx/s)
- Maintenance coefficient (m)
- Substrate affinity constant (Ks)
Correct Answer: Yield coefficient (Yx/s)
Q5. For a batch culture at unlimited substrate (S >> Ks), μ approaches μmax. If μmax = 0.6 h⁻¹, what is the approximate doubling (generation) time?
- 0.69 hours
- 1.16 hours
- 2.31 hours
- 0.12 hours
Correct Answer: 1.16 hours
Q6. Which process condition most commonly leads to oxygen limitation in an aerobic batch culture at large scale?
- Low agitation and inadequate gas transfer (low kLa)
- Excessive antifoam use
- High nutrient concentration
- Too high inoculum purity
Correct Answer: Low agitation and inadequate gas transfer (low kLa)
Q7. In batch culture, substrate inhibition (Haldane kinetics) typically causes which pattern as substrate concentration increases?
- Specific growth rate increases indefinitely with substrate
- Specific growth rate decreases monotonically from zero
- Specific growth rate increases to a maximum then decreases at high substrate
- Specific growth rate is independent of substrate concentration
Correct Answer: Specific growth rate increases to a maximum then decreases at high substrate
Q8. Which analytical method gives an estimate of live biomass concentration rapidly but requires calibration for each organism and medium?
- Colony forming units (CFU) plating
- Dry cell weight measurement
- Optical density (OD) at a specified wavelength
- Total organic carbon (TOC) analysis
Correct Answer: Optical density (OD) at a specified wavelength
Q9. During batch fermentation, secondary metabolites such as many antibiotics are most often produced when?
- During early exponential growth
- During late exponential to stationary phase
- Only during the lag phase
- After complete death of culture
Correct Answer: During late exponential to stationary phase
Q10. Which of the following best distinguishes fed-batch from simple batch operation?
- In fed-batch substrate is added during cultivation but no harvest until end
- Fed-batch always removes biomass continuously
- Batch allows continuous addition and removal of culture
- Fed-batch requires continuous sterile bleed
Correct Answer: In fed-batch substrate is added during cultivation but no harvest until end
Q11. The maintenance coefficient in microbial kinetics describes:
- The maximum biomass yield per substrate
- The substrate consumption rate required for cell maintenance, not for growth
- The Monod half-saturation constant
- The oxygen transfer efficiency
Correct Answer: The substrate consumption rate required for cell maintenance, not for growth
Q12. Which phenomenon explains decreased production of a secondary metabolite when fast carbon catabolism represses secondary pathways?
- Product inhibition
- Catabolite repression (glucose effect)
- Substrate inhibition
- Oxygen limitation
Correct Answer: Catabolite repression (glucose effect)
Q13. In a typical batch growth curve plotted as ln(cell concentration) vs time, the slope during exponential phase equals:
- The yield coefficient Yx/s
- The specific growth rate μ
- The maintenance coefficient m
- The Monod constant Ks
Correct Answer: The specific growth rate μ
Q14. Which strategy would most directly increase final biomass concentration in a batch reactor without changing medium composition?
- Use smaller inoculum volume
- Increase initial substrate concentration (within non-inhibitory limits)
- Decrease agitation speed
- Reduce aeration to zero
Correct Answer: Increase initial substrate concentration (within non-inhibitory limits)
Q15. What is a primary disadvantage of batch culture compared with continuous culture for industrial production?
- Better control of transient behavior
- Lower risk of contamination
- Downtime between batches reduces productivity
- Continuous steady-state operation time is shorter
Correct Answer: Downtime between batches reduces productivity
Q16. Which measurement distinguishes viable cells from total cell count in a culture?
- Optical density (OD)
- Dry cell weight (DCW)
- Colony forming unit (CFU) assay or plate count
- Total protein assay
Correct Answer: Colony forming unit (CFU) assay or plate count
Q17. According to Luedeking-Piret model, the rate of product formation (dp/dt) = α(μX) + βX. What does β represent?
- Growth-associated product coefficient
- Non-growth-associated product formation rate per biomass
- Maintenance energy coefficient
- Substrate inhibition constant
Correct Answer: Non-growth-associated product formation rate per biomass
Q18. Which of the following changes during the stationary phase of a batch culture?
- Specific growth rate (μ) becomes approximately equal to specific death rate
- Biomass concentration increases exponentially
- Substrate concentration rises sharply due to synthesis
- Oxygen transfer becomes irrelevant
Correct Answer: Specific growth rate (μ) becomes approximately equal to specific death rate
Q19. When designing scale-up of a batch aerobic fermenter, which dimensionless parameter is commonly targeted to maintain similar oxygen transfer performance?
- Reynolds number only
- kLa (volumetric mass transfer coefficient)
- P/V (power per unit volume) or maintaining similar kLa
- Surface tension
Correct Answer: P/V (power per unit volume) or maintaining similar kLa
Q20. Which of the following best describes a closed batch culture system?
- Continuous feeding and continuous harvest occur
- No input of substrate or removal of culture during growth
- Substrate is added periodically without sterility concerns
- Culture is continuously diluted with fresh medium
Correct Answer: No input of substrate or removal of culture during growth
