Agricultural/Bioengineering Bioprocess Engineering 1 — Questions and Answers
Question 1: In a batch bioreactor, which growth phase is characterized by microorganisms dividing at their maximum specific growth rate?
- Lag phase
- Log (exponential) phase (Correct answer)
- Stationary phase
- Death phase
Correct answer: Log (exponential) phase
During the log phase, nutrients are abundant and microorganisms divide exponentially at their maximum specific growth rate (μmax).
Question 2: In the Michaelis-Menten enzyme kinetics equation, what does the Michaelis constant (Km) represent?
- Maximum reaction velocity
- Substrate concentration at half-maximum velocity (Correct answer)
- Enzyme concentration at saturation
- Temperature coefficient for enzyme activity
Correct answer: Substrate concentration at half-maximum velocity
Km is the substrate concentration at which the reaction proceeds at half of Vmax, reflecting the affinity between enzyme and substrate.
Question 3: Which bioreactor type is most widely used in industrial fermentation due to its uniform mixing achieved via mechanical agitation?
- Packed bed reactor
- Plug flow reactor
- Stirred tank reactor (STR) (Correct answer)
- Fluidized bed reactor
Correct answer: Stirred tank reactor (STR)
The stirred tank reactor uses an impeller for mechanical agitation, providing uniform mixing of nutrients, cells, and oxygen throughout the vessel.
Question 4: In the oxygen transfer rate equation OTR = kLa(C* − CL), what does the term kLa represent?
- Dissolved oxygen concentration in the liquid
- Oxygen saturation concentration at the interface
- Volumetric mass transfer coefficient (Correct answer)
- Oxygen consumption rate by the cells
Correct answer: Volumetric mass transfer coefficient
kLa is the volumetric mass transfer coefficient, combining the liquid-film coefficient (kL) with the gas-liquid interfacial area per unit volume (a).
Question 5: Which chromatography technique separates proteins based on their net surface charge at a given pH?
- Size exclusion chromatography
- Ion exchange chromatography (Correct answer)
- Reverse-phase chromatography
- Hydrophobic interaction chromatography
Correct answer: Ion exchange chromatography
Ion exchange chromatography retains charged proteins on oppositely charged resin, then elutes them by increasing ionic strength or changing pH.
Question 6: What is the primary operational advantage of continuous fermentation over batch fermentation?
- Lower risk of microbial contamination
- Higher product yield per batch cycle
- Steady-state operation with higher volumetric productivity (Correct answer)
- Simpler equipment design and scale-up
Correct answer: Steady-state operation with higher volumetric productivity
Continuous fermentation maintains steady-state conditions by continuously feeding substrate and withdrawing product, achieving higher sustained volumetric productivity than batch processes.
Question 7: A high Damköhler number (Da >> 1) in a bioprocess indicates that the system is limited by:
- Reaction kinetics
- Mass transfer rate (Correct answer)
- Temperature gradients
- pH fluctuations
Correct answer: Mass transfer rate
Da = reaction rate / mass transfer rate; when Da >> 1, the biochemical reaction proceeds faster than mass transfer can supply substrate or remove product, making mass transfer the limiting step.
Agricultural/Bioengineering Bioprocess Engineering 1
In a batch bioreactor, which growth phase is characterized by microorganisms dividing at their maximum specific growth rate?