Agricultural/Bioengineering Bioprocess Engineering 2

Question 1

In fed-batch fermentation, substrate is added incrementally rather than all at once. What is the primary reason for this feeding strategy?

Accepted Answer

To prevent substrate inhibition and maintain optimal growth conditions

Answer

To reduce the cost of sterilization cycles

Answer

To simplify downstream product recovery

Answer

To minimize oxygen demand in the bioreactor

Question 2

What are the standard conditions for steam sterilization (autoclaving) of fermentation media?

Accepted Answer

121°C for 15–20 minutes at 15 psi

Answer

100°C for 30 minutes at atmospheric pressure

Answer

135°C for 5 minutes at 20 psi

Answer

115°C for 45 minutes at 10 psi

Question 3

The Reynolds number (Re) in a stirred bioreactor is primarily used to determine:

Accepted Answer

Flow regime (laminar vs. turbulent) within the vessel

Answer

Dissolved oxygen uptake rate by cells

Answer

Nutrient diffusion rate through cell membranes

Answer

Cell growth rate under shear stress

Question 4

Which microorganism is the primary industrial producer of citric acid through submerged fermentation?

Accepted Answer

Aspergillus niger

Answer

Saccharomyces cerevisiae

Answer

Escherichia coli

Answer

Bacillus subtilis

Question 5

During bioprocess scale-up from laboratory to industrial scale, which parameter is most commonly kept constant to preserve similar mixing and oxygen transfer characteristics?

Accepted Answer

Power input per unit volume (P/V)

Answer

Aeration rate expressed as vvm (volume of air per volume of liquid per minute)

Answer

Impeller rotational speed (rpm)

Answer

Temperature difference across the vessel wall

Question 6

What is the primary purpose of a dissolved oxygen (DO) probe in a bioreactor control system?

Accepted Answer

To monitor oxygen levels and trigger adjustments in aeration or agitation

Answer

To measure pH changes caused by CO₂ accumulation

Answer

To detect microbial contamination by foreign organisms

Answer

To measure residual substrate concentration online

Question 7

In bioprocess engineering, 'aseptic technique' refers to the set of practices designed to:

Accepted Answer

Prevent contamination of pure microbial cultures by extraneous organisms

Answer

Maximize dissolved oxygen transfer efficiency in bioreactors

Answer

Increase the yield coefficient of the fermentation product

Answer

Immobilize enzymes on solid support matrices