21. A fed-batch reactor containing 1 g.l^-1 of substrate in 2 liters of medium. It is fed with 1 g.l^-1 of substrate at the rate of 1 liter per hour. After 10 hours, the concentration of substrate in the reactor was 0.5 g.l^-1 . The mass of substrate that was used by the culture in the reactor was

A. 2g
B. 6g
C. 8g
D. 12g

22. Toxins accumulated in a reactor can lead to low biomass yields probably due to which of the following?

A. NAD⁺ is diverted away from homeostasis to anabolism
B. ATP is diverted away from homeostasis to anabolism
C. NAD⁺ is diverted away from anabolism to homeostasis
D. ATP is diverted away from anabolism to homeostasis

23. The cellular productivity in a continuous stirred tank fermenter (CSTF) increases with an increase in the dilution rate and reaches a maximum value. If the dilution rate is increased beyond the maximum point, the productivity will

A. decrease abruptly
B. increase
C. increase drastically
D. be zero

24. Fluidized bed bioreactors provide higher mass transfer rates than packed bed bioreactors because

A. mixing is higher in fluidized bed bioreactors
B. particles move with the fluid in a fluidized bed bioreactor
C. immobilized particles are smaller in the fluidized bed bioreactors
D. all of the above

25. In fed-batch fermentation, mass of substrate utilized is calculated using the relationship

A. initial mass of substrate in the reactor + final mass of substrate in the reactor + flow rate x [substrate in the feed] B. initial mass of substrate in the reactor – final mass of substrate in the reactor + flow rate x [substrate in the feed] C. initial mass of substrate in the reactor + final mass of substrate in the reactor – flow rate x [substrate in the feed] D. initial mass of substrate in the reactor + final mass of substrate in the reactor – flow rate