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The correct option is (b) False

To ELABORATE: In internal feedback systems, effluent is removed from the vessel in two streams:

1) FILTERED stream

2) Unfiltered stream

Filtered stream SERVES the purpose of feedback, whereas, Unfiltered stream is UTILISED for product harvesting.

In external feedback systems, Effluent from fermenter is fed through a separator.

Two effluent streams are: 1) Concentrated stream

2) DILUTED stream

Wherein, Concentrated stream serves as feedback and Diluted is used for product harvesting.

Correct option is (a) LAG phase

The best I can explain: Lag time is DEFINED as the INITIAL period in the life of a bacterial population when cells are adjusting to a new environment before STARTING exponential growth. Many FACTORS influence the duration of lag time, including inoculum size, the physiological history of the cells, and the precise physiochemical environment of both the original and the new growth medium.

Right ANSWER is (C) By-product of energy generation

For explanation I would say: The problem of strain degeneration has limited application of LARGE scale continuous culture to biomass and, to a lesser extent, potable and industrial alcohol. The PRODUCTION of alcohol by continuous culture is feasible because it is a byproduct of energy generation and thus, is not a DRAIN on the resources of the organism.

The correct answer is (a) True

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.

Right choice is (b) False

Best explanation: CITRIC acid (citrate) is widely used as a flavour enhancer, a preservative in manufactured foods and an antioxidant. It is PRODUCED as an intermediate of the Krebs cycle under aerobic conditions. Citric acid is MASS produced by continuous fermenter systems from cultures of the fungus Aspergillus niger. Carbohydrates are continuously introduced into the fermenter in order to MAINTAIN the citric acid production. Iron (Fe^2+ ions) is excluded from the mixture in order to slow the further conversion of citric acid within the Krebs cycle. As citric acid accumulates it is extracted as part of the medium that is being continuously withdrawn from the fermenter.

The correct option is (d) Milk

Explanation: Whey is the liquid remaining after milk has been CURDLED and strained. It is a byproduct of the manufacture of cheese or CASEIN and has several commercial uses. Sweet whey is a byproduct PRODUCED during the manufacture of rennet types of hard cheese, like Cheddar or Swiss cheese. Acid whey (also known as SOUR whey) is a byproduct produced during the making of acid types of dairy products, such as COTTAGE cheese or strained yogurt.

Right answer is (d) A very concentrated SOLUTION of the limiting substrate

To explain I would SAY: 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.

Correct answer is (a) True

The explanation: Continuous culture provides a higher degree of control than a batch culture. Growth rates can be regulated and maintained for extended periods. By varying the dilution rate, biomass CONCENTRATION can be CONTROLLED. Secondary metabolite production can be sustained SIMULTANEOUSLY ALONG with growth. In STEADY state continuous culture, mixed cultures can be maintained using chemostat cultures – unlike in a batch process where one organism usually outgrows another.

Correct option is (B) False

Easiest explanation: In batch fermentation, the demands of the culture vary during the fermentation- at the beginning, the oxygen demand is low but towards the end the demand is HIGH, due to the high biomass and the increased viscosity of the BROTH. Also, the AMOUNT of cooling required will increase during the process, as will the degree of pH control. In a continuous process oxygen demand, cooling requirements and pH control should remain constant. THUS, the use of continuous culture should allow for the easier introduction of process automation.

Right choice is (a) True

Explanation: An ALTERNATIVE type of continuous culture to the chemostat is the turbidostat, where the concentration of cells in the culture is kept constant by controlling the FLOW of medium such that the turbidity of the culture is kept within certain, narrow LIMITS.

The CORRECT ANSWER is (b) False

The explanation: The growth rate of the cells will be less than the dilution rate and they will be washed out of the VESSEL at a rate greater than they are being PRODUCED, resulting in a DECREASE in biomass concentration.

Right choice is (b) μmax > D

For explanation: The net change in cell concentration over a TIME period may be EXPRESSED as:

dx/dt = growth – output

dx/dt = μx – Dx

Under steady-state conditions, the cell concentration remains constant, thus dx/dt = 0 and:

μx = Dx

μ = D

Under steady-state conditions the specific growth rate is controlled by the dilution rate. Under BATCH CULTURE conditions an organism will grow at its MAXIMUM specific growth rate and, therefore, it is obvious that a continuous culture may be operated only at dilution rates below the maximum specific growth rate. Thus, within certain limits the dilution rate may be used to control the growth rate of the culture.

The correct CHOICE is (b) g BIOMASS dm^-3h^-1

Explanation: From the following EQUATION:

Rbatch = (xmax – XO) / (ti – tii)

Rbatch is the output of the CULTURE, unit is g biomass dm^-3h^-1.

The correct answer is (b) False

To explain: In the chemostat, in the STEADY state adjusting the concentration of one substrate controls cell growth. In the turbidostat, cell growth is KEPT CONSTANT by using turbidity to monitor the biomass concentration and the rate of feed of nutrient solution is appropriately ADJUSTED. In the chemostat, constant CHEMICAL environment is maintained, while in a turbidostat constant cell concentration is maintained.

Right OPTION is (b) Highly concentrated

For 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.

Right ANSWER is (a) Biomass increases

Best EXPLANATION: The μ declines when the LIMITING substrate CONCENTRATION remains virtually constant, biomass increases and the concentration of the non-limiting NUTRIENTS declines.

Correct choice is (C) The organism is not growing at μmax

The EXPLANATION is: The tii is the time during which the organism is not growing at μmax and includes the LAG PHASE, the DECELERATION phase and the periods of batching, sterilizing and harvesting.

The CORRECT answer is (b) Purify enzymes

Explanation: A fed-batch is a biotechnological batch process which is based on feeding of growth LIMITING NUTRIENT SUBSTRATE to a CULTURE continuous addition of sugars in fed batch fermentation is done to purify enzymes.

Correct ANSWER is (C) Long GROWTH periods of subtrates/microbes

To elaborate: Long growth periods not only increase the risk of contamination but also dictate that the bioreactor must be extremely reliable and consistent, INCURRING a potentially larger initial expenditure in higher quality equipment.

Correct OPTION is (b) Effluent STREAM is less concentrated than in the VESSEL

To explain I would say: INTERNAL feedback means that limiting the exit of biomass form the chemostat such that the biomass in the effluent stream is less concentrated than in the vessel.

The correct choice is (a) Lag phase

For explanation I would say: 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.

The correct ANSWER is (a) Glucose is low

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.

Right CHOICE is (d) IMMOBILIZED CELLS CONSUMES substrate within reactors

Explanation: Wall growth is commonly encountered practical difficulty in which the organism adheres to the inner surfaces of the reactor resulting an increase in heterogeneity. The immobilized cells are not subject to removal from the vessel but will consume substrate resulting in the SUSPENDED biomass concentration being lower than predicted.

Correct choice is (a) Nitrification

Best 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.

The correct option is (a) MUTANT to wild type

The explanation: Mutation can occur in two directions; mutation from wild type to mutant is called a forward mutation, and mutation from mutant to wild type is called a back mutation or REVERSION. Reverse mutation from the aberrant state of a gene back to its NORMAL, or wild type, state can result in a number of possible molecular changes at the protein LEVEL. True reversion is the reversal of the original nucleotide change.

Right OPTION is (b) Sterile water

Explanation: Dilution would be achieved by withdrawing culture and REFILLING to the ORIGINAL level with sterile water or medium not CONTAINING the FEED substrate.

Right choice is (b) Maintenance of MIXED cultures

Easiest explanation: Continuous culture provides a HIGHER degree of control than a batch culture. Growth rates can be regulated and maintained for extended periods. By varying the DILUTION rate, biomass concentration can be controlled. Secondary metabolite production can be sustained simultaneously along with growth. In steady state continuous culture, mixed cultures can be maintained using chemostat cultures – UNLIKE in a batch process where one organism usually outgrows another.

Correct choice is (a) True

The EXPLANATION: The antibiotic penicillin can be mass produced via the use of deep-tank batch fermentation. Penicillium mold is grown in the deep-tank batch fermenters following the addition of SUGARS and other key INGREDIENTS. The production process typically lasts 6 – 8 days, with the fermenter drained at the end of the fermentation cycle. Penicillin is separated from the solution and PURIFIED via downstream PROCESSING to improve its antibiotic potential.

Correct ANSWER is (a) True

Explanation: This is attributed to the phenomenon of microorganisms utilizing a greater proportion of SUBSTRATE for MAINTENANCE at low dilution rates. Effectively, the YIELD factor decreases at low dilution rates.

Right choice is (a) 4.0×10^4 cells, 1.7×10^11 cells

The BEST EXPLANATION: Use the equation X= 2^n X0, where X0 is the initial number of cells, n is the number of generations, and X is the number of cells after n generations.

After 4 h, n=4 h/2 h per GENERATION= 2 generations:

X=2^2 (10^4) = 4.0×10^4 cells

After 48 h, n= 24 generations:

X = 2^24 (10^4) = 1.7×10^11 cells

This REPRESENTS an increase of less than one order of magnitude for the 4-h culture, and seven orders of magnitude for the 48-h culture.

Right answer is (a) Small

To EXPLAIN I WOULD say: 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.

The correct option is (b) False

Best 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.

Correct answer is (b) Animal

To explain: The adoption of continuous culture for animal cell products is even more complex than for microbial systems. Furthermore, it is difficult to MONITOR the genetic stability of cells which are immobilized in a LARGE SCALE REACTOR system. Thus, large scale animal cell products are still PRODUCED by batch methods.

Correct CHOICE is (b) Proteolysis

Best 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.

Right ANSWER is (c) Growth RATE changes variably

Easy 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.