# Bioprocess Engineering Questions and Answers – Fed Batch Culture

This set of Bioprocess Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Fed Batch Culture”.

1. A concentrated solution of the limiting substrate is added in fed-batch at a rate?
a) Greater than the solution of the limiting substrate and the same medium used to establish the batch culture
b) Less than the solution of the limiting substrate and the same medium used to establish the batch culture
c) Equal to the solution of the limiting substrate and to the same medium used to establish the batch culture
d) Negligible to the solution of the limiting substrate and to the same medium used to establish the batch culture

Explanation: A concentrated solution of the limiting substrate is added in fed-batch at a rate less than the solution of the limiting substrate and the same medium used to establish the batch culture, resulting in an increase in volume.

2. Which of the following Fed-batch system is described as a fixed volume?
a) The same medium used to establish the batch culture
b) A solution of the limiting substrate
c) A concentrated solution of the limiting substrate
d) A very concentrated solution of the limiting substrate

Explanation: A very concentrated solution of the limiting substrate added at a rate less than the same medium used to establish the batch culture, a solution of the limiting substrate and a concentrated solution of the limiting substrate, resulting in an insignificant increase in volume.

3. What do you mean by “Quasi steady state”?
a) Cell concentration remains virtually constant
b) Cell concentration is virtually variable
c) Total biomass remains constant with time
d) Total biomass decreases with time

Explanation: The total biomass in the culture (X) increases with time, cell concentration (x) remains virtually constant, that is dx/dt ≅ 0 and therefore μ ≅ D. This situation is termed as a quasi steady state.

4. Quasi – steady state in fed batch is when?
a) Growth rate remains constant
b) Dilution remains constant
c) Growth rate changes variably
d) μ remains constant

Explanation: The major difference between the steady state of a chemostat and the quasi steady state of a fed batch culture is that μ is constant in the chemostat but decreases in fed-batch. However, in the genuine steady state of a chemostat, dilution rate and growth rate are constant whereas in a fed-batch quasi steady state they change over the time of fermentation.

5. In a fixed-volume fed- batch culture μ declines when?
a) Biomass increases
b) Biomass decreases
c) Biomass remains constant
d) Biomass is equal to zero

Explanation: The μ declines when the limiting substrate concentration remains virtually constant, biomass increases and the concentration of the non-limiting nutrients declines.
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6. Dilution refilling is done with______
a) Non- sterile water
b) Sterile water
c) Microbes
d) Waste

Explanation: Dilution would be achieved by withdrawing culture and refilling to the original level with sterile water or medium not containing the feed substrate.

7. What will be the condition when pH will be high?
a) Glucose is low
b) Glucose is equal with biomass concentration
c) Glucose is high with biomass concentration
d) Excess of glucose

Explanation: Glucose starvation may result in the organic nitrogen in the medium being used as a carbon source, resulting in high pH and inadequate biomass formation.

8. Fed-batch culture is superior to conventional batch culture.
a) True
b) False

Explanation: The advantage of the fed-batch culture is that one can control concentration of fed-substrate in the culture liquid at arbitrarily desired levels (in many cases, at low levels). Generally speaking, fed-batch culture is superior to conventional batch culture when controlling concentrations of a nutrient (or nutrients) affect the yield or productivity of the desired metabolite.

9. Fed-batch culture is not used for substrate inhibition.
a) True
b) False

Explanation: Nutrients such as methanol, ethanol, acetic acid, and aromatic compounds inhibit the growth of microorganisms even at relatively low concentrations. By adding such substrates properly lag-time can be shortened and the inhibition of the cell growth markedly reduced.

10. In fed-batch culture, the feed solution is ________
a) Less concentrated
b) Highly concentrated
c) Highly diluted
d) Diluted

Explanation: The fed-batch strategy is typically used in bio-industrial processes to reach a high cell density in the bioreactor. Mostly the feed solution is highly concentrated to avoid dilution of the bioreactor.

11. Organisms in which phase are adapting to the new environment?
a) Lag phase
b) Death phase
c) Exponential phase
d) Stationary phase

Explanation: During batch culture, a typical bacterial growth curve shows five distinct phases of growth: lag phase, the delay before the start of exponential growth; exponential phase, where cell division proceeds at a constant rate; stationary phase, when conditions become unfavorable for growth and bacteria stop replicating; death phase, when cells lose viability; and, finally, long-term stationary phase, which can extend for years. It has been assumed that lag phase allows the adaptation required for bacterial cells to begin to exploit new environmental conditions. This process could include the repair of macromolecular damage that accumulated during stationary phase and the synthesis of cellular components necessary for growth.

12. Which type of media is used for fungi cultivation?
a) Non nutrient agar
b) Sabouraud’s dextrose agar
c) MacConkey’s agar
d) RPMI

Explanation: Sabouraud Agar or Sabouraud Dextrose Agar or SDA is a type of agar growth medium containing peptones. It is used to cultivate dermatophytes and other types of fungi, and can also grow filamentous bacteria such as Nocardia. It has utility for research and clinical care.

13. Conversion of substrate to amino acids is called __________
a) Nitrification
b) Proteolysis
c) Peptidase
d) Deaminase

Explanation: Proteolysis is the breakdown of proteins into smaller polypeptides or amino acids. Uncatalysed, the hydrolysis of peptide bonds is extremely slow, taking hundreds of years. Proteolysis is typically catalysed by cellular enzymes called proteases, but may also occur by intra-molecular digestion. Low pH or high temperatures can also cause proteolysis non-enzymatically.

14. Conversion of substrate to ammonia and organic acid is by _______
a) Nitrification
b) Proteolysis
c) Peptidase
d) Deaminase

Explanation: Nitrification is the biological oxidation of ammonia or ammonium to nitrite followed by the oxidation of the nitrite to nitrate. The transformation of ammonia to nitrite is usually the rate limiting step of nitrification. Nitrification is an important step in the nitrogen cycle in soil. Nitrification is an aerobic process performed by small groups of autotrophic bacteria and archaea.

15. In the fed-batch method the critical elements of the nutrient solution are added in which amount of concentrations at the beginning of the fermentation?
a) Small
b) Large
c) Very large
d) Little

Explanation: Fed-batch cultivation can provide the solution to substrate inhibition problem by slow feeding of nutrients to the bioreactor; however it can still not address the severe inhibition problem due to accumulating high product concentrations. The optimal design of fed-batch cultivation has to take in to account several factors in to consideration for example time to start the fresh nutrient feed (in the end or when the culture is exponentially growing) what should be the substrate concentration in the feed and its rate of addition and when to finish the nutrient feeding so that the highest concentration of product is produced and no unconverted substrate when the reactor is full.

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