Cell yield determination MCQs With Answer

Cell yield determination MCQs With Answer

This set of multiple-choice questions focuses on cell yield determination, a critical topic in bioprocess engineering for M.Pharm students. The quiz emphasizes practical and theoretical methods used to quantify biomass yield from substrates, including gravimetric dry-weight measurements, optical density calibration, stoichiometric and elemental balance approaches, and the impact of maintenance and product formation on yields. Questions explore key formulas (Yx/s, qS, maintenance coefficient), experimental design considerations in batch and fed-batch systems, and instrumentation limits. These MCQs aim to reinforce calculation skills, interpretation of yield data and troubleshooting in fermentation processes, bridging theory with routine lab practice.

Q1. What is the conventional definition of the biomass yield coefficient Yx/s?

• Biomass formed per unit time
• Substrate consumed per unit biomass formed
• Biomass formed per mass of substrate consumed
• Biomass concentration divided by cell number

Correct Answer: Biomass formed per mass of substrate consumed

Q2. What are the typical units for Yx/s when biomass and substrate are measured gravimetrically?

• g substrate / g biomass
• g biomass / g substrate
• g biomass / L
• mol substrate / mol biomass

Correct Answer: g biomass / g substrate

Q3. How is the experimental Yx/s determined from batch cultivation data?

• By dividing final biomass by cultivation time
• From the slope of biomass concentration versus time during stationary phase
• As ΔX/ΔS (change in biomass divided by change in substrate) over the growth period
• By measuring optical density at a single time point

Correct Answer: As ΔX/ΔS (change in biomass divided by change in substrate) over the growth period

Q4. Which method is commonly used to convert spectrophotometric optical density (OD) into biomass for yield calculations?

• Assume OD is equal to biomass concentration without calibration
• Use a standard calibration curve correlating OD to dry cell weight
• Multiply OD by culture volume only
• Calibrate OD with gas uptake rates

Correct Answer: Use a standard calibration curve correlating OD to dry cell weight

Q5. Which empirical elemental formula is often used as an approximate composition for microbial biomass in stoichiometric calculations?

• CH2O
• CH1.8O0.5N0.2
• C6H12O6
• CO2

Correct Answer: CH1.8O0.5N0.2

Q6. How does an increased maintenance energy requirement affect observed biomass yield?

• It increases Yx/s because more energy is available
• It decreases Yx/s because substrate is diverted to non-growth maintenance
• It has no effect on yield, only on growth rate
• It transforms biomass into product increasing yield

Correct Answer: It decreases Yx/s because substrate is diverted to non-growth maintenance

Q7. What is the difference between apparent yield and true yield in fermentation?

• Apparent yield is calculated from cell count; true yield uses OD
• Apparent yield ignores maintenance and product formation while true yield accounts for all substrate sinks
• There is no difference; both terms are interchangeable
• Apparent yield uses theoretical stoichiometry; true yield uses experimental data

Correct Answer: Apparent yield ignores maintenance and product formation while true yield accounts for all substrate sinks

Q8. Which relationship correctly links specific substrate uptake rate qS, specific growth rate μ, yield Yx/s and maintenance mS?

• qS = μ × Yx/s + mS
• qS = μ / Yx/s + mS
• qS = Yx/s / μ + mS
• qS = μ – Yx/s × mS

Correct Answer: qS = μ / Yx/s + mS

Q9. Which biomass measurement method is considered the most direct and accurate for yield determination?

• Optical density only
• Dry cell weight (gravimetric)
• Cell counting by hemocytometer without calibration
• Estimating from medium turbidity visually

Correct Answer: Dry cell weight (gravimetric)

Q10. What is a principal limitation of using turbidity (OD) measurements for cell yield determination?

• OD directly measures substrate concentration, not cells
• OD is unaffected by cell size and shape
• OD can be influenced by cell size, shape, clumping and presence of dead cells
• OD gives absolute dry weight without calibration

Correct Answer: OD can be influenced by cell size, shape, clumping and presence of dead cells

Q11. Which approach uses measurement of CO2 and other carbon outputs to estimate biomass yield?

• Optical calibration method
• Carbon balance (elemental balance) approach
• Microscopy-based counting
• pH-stat control method

Correct Answer: Carbon balance (elemental balance) approach

Q12. When performing stoichiometric calculations to estimate theoretical biomass yield from glucose, which basis is commonly used?

• Mass basis without considering elemental composition
• Molar carbon (C-moles) or elemental basis using empirical biomass formula
• Volume of culture only
• OD units directly converted to moles

Correct Answer: Molar carbon (C-moles) or elemental basis using empirical biomass formula

Q13. What adjustment is essential when calculating yield in a fed-batch fermentation?

• Ignore substrate fed after inoculation
• Account for cumulative substrate added, substrate consumed and any sampling/evaporation
• Assume constant substrate concentration throughout
• Calculate yield using only final biomass and initial substrate

Correct Answer: Account for cumulative substrate added, substrate consumed and any sampling/evaporation

Q14. Which instrument provides rapid single-cell counts and can assist in converting cell number to biomass for yield estimation?

• pH meter
• Flow cytometer
• Standard laboratory balance
• Spectrophotometer without calibration

Correct Answer: Flow cytometer

Q15. What are the units of the maintenance coefficient mS used in substrate balance equations?

• g biomass / g substrate / h
• g substrate / g biomass / h
• mol substrate / L
• h^-1

Correct Answer: g substrate / g biomass / h

Q16. How do aerobic conditions typically influence biomass yield compared with anaerobic conditions for the same substrate?

• Aerobic yields are generally lower than anaerobic yields
• Aerobic yields are generally higher due to more efficient ATP generation by respiration
• There is no systematic difference
• Anaerobic yields are always double aerobic yields

Correct Answer: Aerobic yields are generally higher due to more efficient ATP generation by respiration

Q17. What is a typical range for Yx/s (g biomass/g glucose) for many heterotrophic bacteria growing on glucose?

• 0.01–0.05 g/g
• 0.4–0.6 g/g
• 1.5–2.0 g/g
• 5–10 g/g

Correct Answer: 0.4–0.6 g/g

Q18. To compute biomass yield from OD measurements, what two steps are essential?

• Measure OD and assume yield equals OD
• Calibrate OD to dry weight (biomass) and compute ΔX/ΔS
• Convert OD to cell number and ignore substrate data
• Use OD at only one time point and multiply by culture volume

Correct Answer: Calibrate OD to dry weight (biomass) and compute ΔX/ΔS

Q19. How does formation of a non-growth-associated product affect observed biomass yield on substrate?

• It increases biomass yield because more substrate is consumed
• It decreases biomass yield because substrate is diverted to product formation rather than biomass
• It converts maintenance energy into biomass increasing yield
• It has no effect on biomass yield

Correct Answer: It decreases biomass yield because substrate is diverted to product formation rather than biomass

Q20. Which method allows estimation of the theoretical maximum biomass yield from a substrate?

• Empirical OD reading without calibration
• Stoichiometric elemental balancing using biomass formula and degree of reduction
• Measuring only oxygen uptake
• Visual turbidity comparison

Correct Answer: Stoichiometric elemental balancing using biomass formula and degree of reduction

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