Fermentation Reactors Questions and Answers

Multiple Choice Questions (MCQ) and Answers on Fermentation Reactors

Question 1: Unsteady state mass balance for dynamic model of continuous stirred tank reactor (CSTR) is

  1. time rate of total amount in rector = rate of addition to reactor -rate of removal + rate of formation
  2. total amount in rector = rate of addition to reactor – rate of removal + rate of formation
  3. rate of total amount in rector = rate of addition to reactor – rate of removal + rate of formation
  4. none of the above

Answer: 1

Question 2: A fed-batch reactor initially contains 2 litre of medium. If it was fed at 1 litre per hour, then after 10 hours, the volume of the reactor will be

  1. 1 litre
  2. 2 litre
  3. 3 litre
  4. 13 litre

Answer: 2

Question 3: A Bacillus sp. produces an antibiotic only during the stationary phase when grown in a batch culture. If grown in a 5 litre continuous culture, the steady state productivity of the antibiotic

  1. will increase until the culture washes out
  2. will decrease after washout
  3. will be zero
  4. will be infinite

Answer: 3

Question 4: In a fluidized bed reactor, the function of the disengagement zone is to

  1. reduce loss of particles from the reactor
  2. reduce the velocity of the particles near the surface of the reactor
  3. reduce foaming problems
  4. all of the above

Answer: 4

Question 5: Saccharomyces cerevisiae produces high biomass yields at low glucose concentrations and high dissolved oxygen concentrations. Which of the following should be followed for maximizing its biomass productivity?

  1. Batch fermenter with a high initial glucose concentration
  2. Continuous fermenter with a low initial glucose concentration
  3. Fed batch fermenter
  4. All of the above

Answer: 3

Question 6: The main reason for production of antibiotics in fed batch reactors is

  1. the presence of precursors is often toxic to the cells
  2. higher yields when cells enter the stationary phase
  3. higher yields when cell growth slows
  4. all of the above

Answer: 4

Question 7: Fed batch reactors is used to produce vinegar because

  1. it can maintain low ethanol concentrations
  2. it can maintain low acetic acid concentrations
  3. acetic acid bacteria tend to ferment at high ethanol concentrations\
  4. all of the above

Answer: 1

Question 8: When a culture of fermenting yeast becomes metabolically uncoupled, ethanol

  1. becomes a secondary metabolite
  2. production becomes growth associated
  3. production becomes non-growth associated
  4. becomes a growth nutrient

Answer: 3

Question 9: Mixing profiles closest to plug flow are observed in

  1. continuous packed bed reactor
  2. stirred tank reactor with biomass recycles
  3. continuous fluidized bed bioreactor
  4. all of these

Answer: 1

Question 10: On a glucose medium, the growth of an organism is characterized by the following Monod model and stoichiometric parameters μm = 0.3 h-1, Ks =0.05 g.l-1 and Yxs = 0.3 g.g-1 When this organism is grown in a 2 litre continuous on a medium containing 10 g.l-1 of glucose added at 1 l.h-1, the steady state concentration of biomass in the reactor will be

  1. 0 g.l-1
  2. 0.4 g.l-1
  3. 0.5 g.l-1
  4. 10 g.l-1

Answer: 1

Question 11: A chemostat has a liquid volume of 2 litres and is being fed at a rate of 4 litres per hour. Dilution rate for this reactor will be

  1. 2 litres
  2. 2 litres per hour
  3. 2 h-1
  4. 4 litres per hour

Answer: 3

Question 12: Mixing per unit volume is observed to be poorest in

  1. continuous packed bed reactor
  2. continuous fluidized bed bioreactor
  3. continuous airlift bioreactor
  4. none of the above

Answer: 1

Question 13: The growth of an organism on glucose is described by the following Monod model parameters: μm = 0.5 h-1 and Ks =0.1 g.l-1, if the concentration of glucose in the feed is 10 g.l-1 and the dilution rate is set to 0.4 h-1, then the steady state concentration of glucose in the effluent will be

  1. 0 g.l-1
  2. 0.5 g.l-1
  3. 1.0 g.l-1
  4. 10 g.l-1

Answer: 2

Question 14: A continuous reactor at steady state contains 0.04 g.l-1 of biomass and 0.02 g.l-1 of phenol. The feed contained 0.1 g.l-1 of phenol. The biomass yield would be

  1. 0.4 g.g-1
  2. 0.5 g.g-1
  3. 1.0 g.g-1
  4. 5.0 g.g-1

Answer: 2

Question 15: A culture system with constant environmental conditions maintained through continual provision of nutrient and removal of wastes is called __________ culture system.

  1. continuous
  2. batch
  3. fed-batch
  4. semi continuous

Answer: 1

Question 16: A fed-batch reactor containing 1 g.l-1 of substrate in 2 litre of medium. It is fed with 1 g.l-l of substrate at the rate of 1 litre 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

  1. 2g
  2. 6g
  3. 8g
  4. 12g

Answer: 2

Question 17: Toxins accumulated in a reactor can lead to low biomass yields probably due to which of the following?

  1. NAD+ is diverted away from homeostasis to anabolism
  2. ATP is diverted away from homeostasis to anabolism
  3. NAD+ is diverted away from anabolism to homeostasis
  4. ATP is diverted away from anabolism to homeostasis

Answer: 4

Question 18: 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

  1. decrease abruptly
  2. increase
  3. increase drastically
  4. be zero

Answer: 1

Question 19: Fluidized bed bioreactors provide higher mass transfer rates than packed bed bioreactors because

  1. mixing is higher in fluidized bed bioreactors
  2. particles move with the fluid in a fluidized bed bioreactor
  3. immobilized particles are smaller in the fluidized bed bioreactors
  4. all of the above

Answer: 2

Question 20: In fed-batch fermentation, mass of substrate utilized is calculated using the relationship

  1. initial mass of substrate in the reactor + final mass of substrate in the reactor + flow rate x [substrate in the feed]
  2. initial mass of substrate in the reactor – final mass of substrate in the reactor + flow rate x [substrate in the feed]
  3. initial mass of substrate in the reactor + final mass of substrate in the reactor – flow rate x [substrate in the feed]
  4. initial mass of substrate in the reactor + final mass of substrate in the reactor – flow rate

Answer: 2

Question 21: A continuous reactor has a dilution rate of 0.5 h-1. Its residence time would be

  1. ln(2)/0.5
  2. ln(2) x 0.5
  3. 0.5 h
  4. 2 h

Answer: 4

Question 22: Which of the following is used to calculate mass of substrate in the reactor?

  1. Flow rate x substrate concentration in the reactor
  2. Volume of reactor x substrate concentration in reactor
  3. Flow rate x mass of reactor
  4. Volume of reactor x Flow rate

Answer: 2

Question 23: If biomass yields are constant, then the biomass productivity of a culture grown in continuous reactor will

  1. always decrease with dilution rate
  2. increase with dilution rate until washout
  3. remain constant irrespective of the dilution rate
  4. decrease with dilution rate until washout

Answer: 2

Question 24: Low dissolved oxygen concentrations leads to

  1. low biomass yields
  2. high biomass yields
  3. no effect on biomass yields
  4. none of the above

Answer: 1

Question 25: In a continuous reactor, the medium contains 40 g.l-1 of maltose and the medium flow rate is 10 litres per hour and the effluent contains 20 g.l-l of lactate. What is the productivity of lactate production from this reactor?

  1. 50 g maltose.l-1
  2. 50 g lactate.l-1
  3. 200 g maltose.l-1
  4. 200 g lactate.l-1

Answer: 4

Question 26: Which of the statement is true for continuous reactor at steady state?

  1. The rates of biomass, substrate and product concentrations are zero
  2. Biomass, substrate and product concentrations are zero
  3. Biomass, substrate and product concentrations do not change with time
  4. Biomass, substrate and product concentrations change with time

Answer: 3

Question 27: A continuous bioreactor in which only the flow rate is used to control the rate of cell or product productivity is called

  1. turbidostat
  2. chemostat
  3. level stat
  4. pH

Answer: 2

Question 28: For organisms growing in a chemostat, the specific growth rate

  1. cannot be determined
  2. can be determined from the dilution rate
  3. equals to the maximum specific growth rate of the culture
  4. none of the above

Answer: 2

Question 29: Saccharomyces cerevisiae is being grown in a chemostat converts glucose to biomass, ethanol, glycerol and carbon dioxide. At steady state, the concentration of glucose, biomass, ethanol and glycerol will

  1. decrease with time
  2. increase with time
  3. be constant
  4. change randomly with time

Answer: 3

Question 30: In aerobic yeast fermentation for production of citric acid from alkanes using a fed-batch culture, why alkanes are slowly fed to the yeast?

  1. Citric acid is toxic to the cells
  2. Alkanes cause foaming
  3. Fast addition of alkanes will inhibit the cells and reduce oxygen transfer rates
  4. Fast addition of alkanes will cause the cells to grow too quickly

Answer: 3

Question 31: Mixing in an anaerobic sludge blanket reactor is due to

  1. rapid change in water temperatures throughout the reactor
  2. release of gases by the microbial populations
  3. swimming of microbes
  4. none of the above

Answer: 2

Question 32: In batch culture, protogon is produced from peptone during the stationary phase with a yield of 0.4 protogon mg per g of peptone. If it is to be produced in a chemostat at a dilution rate of 0.5 h-1 from a medium containing 10 g.l-1 of peptone, then the rate of protogon synthesis would be

  1. 0 g.l-1h-1
  2. 0.5 g.l-1h-1
  3. 1 g.l-1h-1
  4. 2 g.l-1h-1

Answer: 1

Question 33: Formation of end product by Lactococcus lactis will become non-growth associated as lactic acid accumulates because

  1. cells will redirect ATP to anabolism
  2. cells will redirect NAD+ to anabolism
  3. cells will redirect ATP to facilitate the diffusion of lactic acid and H+ out of the cells
  4. cells will redirect ATP to the active transport of lactic acid and H+ out of the cells

Answer: 4

Question 34: Which of the following would not be subjected to the “glucose effect”?

  1. Aspergillus fumigatus
  2. Saccharomyces cerevisiae
  3. Escherichia coli
  4. Aspergillus niger

Answer: 3

Question 35: Immobilized cell reactors for wastewater treatment have the advantage of having/being

  1. higher cell concentration
  2. more stable and prevent washout
  3. higher dilution rate before the cells washout
  4. all of the above

Answer: 4

Question 36: Yield coefficient represents

  1. total biomass or product produced
  2. conversion efficiency of a substrate into product
  3. conversion rate of a substrate into biomass or product
  4. production time of biomass or product

Answer: 2

Question 37: The lowest biomass yield in a culture of Escherichia coli will be in

  1. an aerated batch culture containing a initial high concentration of glucose
  2. an aerated batch reactor containing an initial low concentration of glucose
  3. an aerated fed-batch reactor having a low glucose concentration
  4. an aerated continuous reactor having a low glucose concentration

Answer: 1

Question 38: When two populations compete for a single growth limiting substrate in a continuous fermenter, which organism would not be washed out?

  1. Organism maintaining the highest substrate concentration’
  2. Organism maintaining the lowest substrate concentration
  3. Both (1) and (2)
  4. Organism maintaining the moderate substrate concentration

Answer: 2

Question 39:  The continuous cultures are not widely used in industry because

  1. they are not suited for the production of secondary metabolites
  2. contamination or mutation can have a disastrous effect on the operation
  3. the government will not approve the licensing of pharmaceuticals produced in continuous cultures
  4. all of the above

Answer: 4

Question 40: The lowest yield of ATP /is in

  1. fermentation
  2. aerobic respiration
  3. anaerobic respiration
  4. same in (1), (2) and (3)

Answer: 1