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
- time rate of total amount in rector = rate of addition to reactor -rate of removal + rate of formation
- total amount in rector = rate of addition to reactor – rate of removal + rate of formation
- rate of total amount in rector = rate of addition to reactor – rate of removal + rate of formation
- 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 litre
- 2 litre
- 3 litre
- 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
- will increase until the culture washes out
- will decrease after washout
- will be zero
- will be infinite
Answer: 3
Question 4: In a fluidized bed reactor, the function of the disengagement zone is to
- reduce loss of particles from the reactor
- reduce the velocity of the particles near the surface of the reactor
- reduce foaming problems
- 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?
- Batch fermenter with a high initial glucose concentration
- Continuous fermenter with a low initial glucose concentration
- Fed batch fermenter
- All of the above
Answer: 3
Question 6: The main reason for production of antibiotics in fed batch reactors is
- the presence of precursors is often toxic to the cells
- higher yields when cells enter the stationary phase
- higher yields when cell growth slows
- all of the above
Answer: 4
Question 7: Fed batch reactors is used to produce vinegar because
- it can maintain low ethanol concentrations
- it can maintain low acetic acid concentrations
- acetic acid bacteria tend to ferment at high ethanol concentrations\
- all of the above
Answer: 1
Question 8: When a culture of fermenting yeast becomes metabolically uncoupled, ethanol
- becomes a secondary metabolite
- production becomes growth associated
- production becomes non-growth associated
- becomes a growth nutrient
Answer: 3
Question 9: Mixing profiles closest to plug flow are observed in
- continuous packed bed reactor
- stirred tank reactor with biomass recycles
- continuous fluidized bed bioreactor
- 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
- 0 g.l-1
- 0.4 g.l-1
- 0.5 g.l-1
- 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
- 2 litres
- 2 litres per hour
- 2 h-1
- 4 litres per hour
Answer: 3
Question 12: Mixing per unit volume is observed to be poorest in
- continuous packed bed reactor
- continuous fluidized bed bioreactor
- continuous airlift bioreactor
- 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
- 0 g.l-1
- 0.5 g.l-1
- 1.0 g.l-1
- 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
- 0.4 g.g-1
- 0.5 g.g-1
- 1.0 g.g-1
- 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.
- continuous
- batch
- fed-batch
- 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
- 2g
- 6g
- 8g
- 12g
Answer: 2
Question 17: Toxins accumulated in a reactor can lead to low biomass yields probably due to which of the following?
- NAD+ is diverted away from homeostasis to anabolism
- ATP is diverted away from homeostasis to anabolism
- NAD+ is diverted away from anabolism to homeostasis
- 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
- decrease abruptly
- increase
- increase drastically
- be zero
Answer: 1
Question 19: Fluidized bed bioreactors provide higher mass transfer rates than packed bed bioreactors because
- mixing is higher in fluidized bed bioreactors
- particles move with the fluid in a fluidized bed bioreactor
- immobilized particles are smaller in the fluidized bed bioreactors
- all of the above
Answer: 2
Question 20: In fed-batch fermentation, mass of substrate utilized is calculated using the relationship
- initial mass of substrate in the reactor + final mass of substrate in the reactor + flow rate x [substrate in the feed]
- initial mass of substrate in the reactor – final mass of substrate in the reactor + flow rate x [substrate in the feed]
- initial mass of substrate in the reactor + final mass of substrate in the reactor – flow rate x [substrate in the feed]
- 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
- ln(2)/0.5
- ln(2) x 0.5
- 0.5 h
- 2 h
Answer: 4
Question 22: Which of the following is used to calculate mass of substrate in the reactor?
- Flow rate x substrate concentration in the reactor
- Volume of reactor x substrate concentration in reactor
- Flow rate x mass of reactor
- 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
- always decrease with dilution rate
- increase with dilution rate until washout
- remain constant irrespective of the dilution rate
- decrease with dilution rate until washout
Answer: 2
Question 24: Low dissolved oxygen concentrations leads to
- low biomass yields
- high biomass yields
- no effect on biomass yields
- 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?
- 50 g maltose.l-1
- 50 g lactate.l-1
- 200 g maltose.l-1
- 200 g lactate.l-1
Answer: 4
Question 26: Which of the statement is true for continuous reactor at steady state?
- The rates of biomass, substrate and product concentrations are zero
- Biomass, substrate and product concentrations are zero
- Biomass, substrate and product concentrations do not change with time
- 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
- turbidostat
- chemostat
- level stat
- pH
Answer: 2
Question 28: For organisms growing in a chemostat, the specific growth rate
- cannot be determined
- can be determined from the dilution rate
- equals to the maximum specific growth rate of the culture
- 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
- decrease with time
- increase with time
- be constant
- 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?
- Citric acid is toxic to the cells
- Alkanes cause foaming
- Fast addition of alkanes will inhibit the cells and reduce oxygen transfer rates
- 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
- rapid change in water temperatures throughout the reactor
- release of gases by the microbial populations
- swimming of microbes
- 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
- 0 g.l-1h-1
- 0.5 g.l-1h-1
- 1 g.l-1h-1
- 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
- cells will redirect ATP to anabolism
- cells will redirect NAD+ to anabolism
- cells will redirect ATP to facilitate the diffusion of lactic acid and H+ out of the cells
- 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”?
- Aspergillus fumigatus
- Saccharomyces cerevisiae
- Escherichia coli
- Aspergillus niger
Answer: 3
Question 35: Immobilized cell reactors for wastewater treatment have the advantage of having/being
- higher cell concentration
- more stable and prevent washout
- higher dilution rate before the cells washout
- all of the above
Answer: 4
Question 36: Yield coefficient represents
- total biomass or product produced
- conversion efficiency of a substrate into product
- conversion rate of a substrate into biomass or product
- production time of biomass or product
Answer: 2
Question 37: The lowest biomass yield in a culture of Escherichia coli will be in
- an aerated batch culture containing a initial high concentration of glucose
- an aerated batch reactor containing an initial low concentration of glucose
- an aerated fed-batch reactor having a low glucose concentration
- 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?
- Organism maintaining the highest substrate concentration’
- Organism maintaining the lowest substrate concentration
- Both (1) and (2)
- Organism maintaining the moderate substrate concentration
Answer: 2
Question 39: The continuous cultures are not widely used in industry because
- they are not suited for the production of secondary metabolites
- contamination or mutation can have a disastrous effect on the operation
- the government will not approve the licensing of pharmaceuticals produced in continuous cultures
- all of the above
Answer: 4
Question 40: The lowest yield of ATP /is in
- fermentation
- aerobic respiration
- anaerobic respiration
- same in (1), (2) and (3)
Answer: 1