Answer: c [Reason:] Aeration is generally accomplished in a separate vessel; if air is sparged directly into the bed, bubble coalescence produces gas pockets and flow channelling or maldistribution. Packed beds are unsuitable for processes which produce large quantities of carbon dioxide or other gases which can become trapped in the packing.

Answer: d [Reason:] HRT also known as hydraulic residence time is a measure of the average length of time that a soluble compound remains in a constructed bioreactor. Hydraulic retention time is the volume of the aeration tank divided by the influent flow rate:

where HRT is hydraulic retention time (d) and usually expressed in hours (or sometimes days), the V is the volume of aeration tank or reactor volume (m3), and is the influent flow rate (m3/d).

Answer: b [Reason:] The reverse of HRT is defined as dilution rate, for which if it is bigger than the growth rate of microbial cells in the reactor, the microbe will be washed out, and otherwise the microbe will be accumulated in the reactor. Either of these situations may result in the breakdown of the biological process happening in the reactor.

Answer: c [Reason:] The sudden widening at the top of the reactor slows the bubble velocity and thus disengages the bubbles from the liquid flow. Carbon-dioxide rich bubbles are thus prevented from entering the downcomer. The increase in area will also helps to stretch bubbles in foams, causing the bubbles to burst. The axial flow circulation caused by the draft tube also helps to reduce foaming.

Answer: a [Reason:] If foaming is a problem, a supplementary impeller called a foam breaker may be installed. Alternatively, chemical antifoam agents are added to the broth; because antifoams reduce the rate of oxygen transfer, mechanical foam dispersal is generally preferred.

Answer: b [Reason:] Homogeneous flow occurs only at low gas flow rates and when bubbles leaving the sparger are evenly distributed across the column cross-section. In homogeneous flow, all bubbles rise with the same upward velocity and there is no backmixing of the gas phase.

Answer: c [Reason:] In continuous stirred tank reactor, Mixing and bubble dispersion are achieved by mechanical agitation; this requires a relatively high input of energy per unit volume. A wide variety of impeller sizes and shapes is available to produce different flow patterns inside the vessel; in tall fermenters, installation of multiple impellers improves mixing.

Answer: a [Reason:] In the internal-loop vessels, the riser and down comer are separated by an internal baffle or draft tube; air may be sparged into either the draft tube or the annulus. In the external-loop or outer-loop airlift, separate vertical tubes are connected by short horizontal sections at the top and bottom. Because the riser and downcomer are further apart in external-loop vessels, gas disengagement is more effective than in internal-loop devices. Fewer bubbles are carried into the downcomer, the density difference between fluids in the riser and downcomer is greater, and circulation of liquid in the vessel is faster.

Answer: b [Reason:] Airlift reactors generally provide better mixing than bubble columns except at low liquid velocities. The airlift configuration confers a degree of stability to liquid flow compared with bubble columns; therefore, higher gas flow rates can be used without incurring operating problems such as slug flow or “spray formation”.

Answer: c [Reason:] The draft tube is a conduit which connects the runner exit to the tail race where the water is being finally discharged from the turbine. The primary function of the draft tube is to reduce the velocity of the discharged water to minimize the loss of kinetic energy at the outlet. This draft tube at the end of the turbine increases the pressure of the exiting fluid at the expense of its velocity. This means that the turbine can reduce pressure to a higher extent without fear of back flow from the tail race.

Answer: a [Reason:] Large airlift reactors with capacities of thousands of cubic metres have been constructed. Tall internal-loop airlifts built underground are known as deep- shaft reactors; very high hydrostatic pressure at the bottom of these vessels considerably improves gas-liquid mass-transfer. The height of airlift reactors is typically about 10 times the diameter; for deep-shaft systems the height-to-diameter ratio may be increased up to 100.

Answer: b [Reason:] If the culture has high viscosity, sufficient mixing and mass transfer cannot be provided by air-driven reactors. Stirred vessels are more suitable for viscous liquids because greater power can be input by mechanical agitation. Nevertheless, mass- transfer rates decline rapidly in stirred vessels at viscosities greater than 50-100 cP.

Answer: d [Reason:] Trickle bed reactors are a class of packed bed reactors in which the medium flows (or trickles) over the solid particles. In these reactors, the particles are not immersed in the liquid. The liquid medium trickles over the surface of the solids on which the cells are immobilized.

Answer: a [Reason:] Fluidised beds can also be used with microcarrier beads used in attached animal cell culture. Fluidised-bed microcarrier cultures can be operated both in batch and continuous mode. In the former the fermentation fluid is recycled in a pump-around loop.

Answer: a [Reason:] Up and down agitators are useful to avoid shear stress to the cells. These are done by instead of a traditional propeller agitator, which requires an expensive motor and magnetic coupling. Vertical up and down motion is achieved by a motor together with an inexpensive membrane perfectly assure sterility and produce an efficient mixing without formation of a vortex (no baffles needed). At the same time this type of mixing is gentler on cells and produces less foam.

Answer: b [Reason:] A stem cell is an undifferentiated cell capable of continuous self-renewal that can also produce large numbers of differentiated progeny, depending on extracellular factors.

Answer: c [Reason:] Hematopoietic stem cells (HSCs) are the stem cells that give rise to blood cells through the process of haematopoiesis. They are derived from mesoderm and located in the red bone marrow, which is contained in the core of most bones.

Answer: b [Reason:] These non-hematopoietic stem cells make up a small proportion of the stromal cell population in the bone marrow and can generate bone, cartilage, and fat cells that support the formation of blood and fibrous connective tissue.

Answer: b [Reason:] The lymphoreticular system consists of the spleen, lymphnodes, lymphatic vessels, thymus, and bone marrow. The functions of these systems include immune defense, transport of fats throughout the body, and collection and transport of interstitial fluid (the fluid bathing the cells) back to the circulatory system.

Answer: b [Reason:] The key ethical issues concern the destruction of human embryos for stem cell derivation. On the grounds that the human embryo is a human life with moral value justifying its protection, the extraction of embryonic stem cells is unethical.

Answer: a [Reason:] This might cause you to worry that this means cancer, but atypical cells aren’t necessarily cancerous. The presence of atypical cells is sometimes referred to as “dysplasia.” Many factors can make normal cells appear atypical, including inflammation and infection. Even normal aging can make cells appear abnormal.

Answer: c [Reason:] The act or process of culturing two types of cells or tissue in the same medium.

Answer: a [Reason:] Fluidized bed reactors with macroporous supports mimic structures much like that in bone. However, there are challenges in controlling surface chemistry and maintaining the appropriate mix of cell types. Cell sampling and control of reactor conditions can be problematic.

Answer: c [Reason:] Spheroids are a type of three-dimensional cell modeling that better simulate a live cell’s environmental conditions compared to a two-dimensional cell model, specifically with the reactions between cells and the reactions between cells and the matrix. Spheroids are useful in the study of changing physiological characteristics of cells, the difference in the structure of healthy cells and tumor cells, and the changes cells undergo when forming a tumor.

Answer: c [Reason:] The “T” referred to the total surface area of the flask that was available for cell growth: thus a T-25 flask had a 25cm² growth area. By the 1960s, straight neck T-flasks was available molded from polystyrene that was treated to enhance cell attachment.

nswer: b [Reason:] An extracorporeal is a medical procedure which is performed outside the body.

Answer: c [Reason:] An extracorporeal device to serve as temporary assist device is realistic (such a system is in clinical trials). A promising design is a hollow-fiber system using porcine (pig) hepatocytes. Such cells are relatively easy to obtain in large quantities and maintain a satisfactory level of differentiated cellular activity in regard to detoxification. A disadvantage is due to limited lifespan (and proliferative ability).

Answer: b [Reason:] A bioartificial liver device (BAL) is an artificial extracorporeal supportive device for an individual who is suffering from acute liver failure.

Answer: a [Reason:] Living-Donor Liver Transplants. Because your liver grows back, you can actually donate a piece of your liver to someone else. After surgery, your liver will regenerate back to its full size. The other person’s new liver will grow back as well, leaving both people with healthy, functioning livers.

Answer: d [Reason:] The liver has two large sections, called the right and the left lobes. The liver also detoxifies chemicals and metabolizes drugs. As it does so, the liver secretes bile that ends up back in the intestines. The liver also makes proteins important for blood clotting and other functions.

Answer: a [Reason:] Many media are buffered at about pH 7.0 by the incorporation of calcium carbonate. If the pH decreases the carbonate is decomposed.

Answer: c [Reason:] When a drop of decinormal HCL is added to a mixture of weak acid and its strong salt (e. g. , CH₃COOH + CH₃COONa) there is a very slight change of H⁺ ion concentration. It means the pH value in these media remains approximately the same and these solutions resist any change of acidity or alkalinity.

Answer: c [Reason:] When a decinormal solution of NaOH is added in a mixture of weak base and its strong salt (e. g.,NH₄OH + NH₄Cl) then a slight change in OH ion concentration takes place. It means the pH value in these media remains approximately the same and these solutions resist any change of acidity or alkalinity.

Answer: c [Reason:] H₃PO₄ + NaH₂PO₄ is a type of mixed buffer of acidic buffer mixture which is combination of a weak acid with its salt of strong base.

Answer: a [Reason:] Na₂HPO₄ + Na₃PO₄ is a type of simple buffer which is a combination of a mixture of an acid salt and normal salt of a poly basic acid.

Answer: c [Reason:] H₂CO₃+Na₂CO₃ is a type of mixed buffer of acidic buffer mixture which is combination of a weak acid with its salt of strong base.

Answer: d [Reason:] The molecular weight of water is 18.015 g/mol.

Answer: b [Reason:] The character of acidic, basic and neutral is defined by the concentration of hydrogen ions [H⁺](mol/L). A solution with a concentration of hydrogen ions higher than 10-7mol/L is acidic, and a solution with a lower concentration is alkaline (another way to say basic).

Answer: d [Reason:] The reaction does not form very much H3O+ or OH-. In one liter of water there are about 55 moles of water molecules, but only 1.0 x 10-7moles of H3O+ and OH- are formed (at room temperature).

Answer: c [Reason:] A buffer solution (more precisely, pH buffer or hydrogen ion buffer) is an aqueous solution consisting of a mixture of a weak acid and its conjugate base, or vice versa.

Answer: a [Reason:] The buffer capacity depends essentially on 2 factors: Ratio of the salt to the acid or base. The buffer capacity is optimal when the ratio is 1:1; that is, when pH = pKa. Total buffer concentration.

Answer: c [Reason:] A buffer is a special solution that stops massive changes in pH levels. Every buffer that is made has a certain buffer capacity, and buffer range. The buffer capacity is the amount of acid or base that can be added before the pH begins to change significantly. It can be also defined as the quantity of strong acid or base that must be added to change the pH of one liter of solution by one pH unit. The buffer range is the pH range where a buffer effectively neutralizes added acids and bases, while maintaining a relatively constant pH.

Answer: d

Answer: c

Explanation: NaOH is a strong base. It will react nearly quantitatively with HOAc to produce OAc-.

Answer: c [Reason:] After the addition of another 0.012 moles of NaOH, all of the HOAc has been converted to NaOAc. thus, [OAc-] = 0.02 M. Since only the “base form” of the HOAc is now present,

Answer: b [Reason:] From the following equation:

R_batch = (x_max – x_o)/ (t_i – t_ii)

R_batch is the output of the culture, unit is g biomass dm^-3h^-1.

Answer: c [Reason:] 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.

Answer: a [Reason:] The productivity in batch culture is at its maximum only towards the end of the process.
For a continuous culture operating at the optimum dilution rate, under steady – state conditions, the productivity will be constant and always maximum. Thus, the productivity of the continuous culture must be greater than the batch.

Answer: b [Reason:] 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.

Answer: a [Reason:] 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.

Answer: c [Reason:] 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.

Answer: b [Reason:] 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.

Answer: b [Reason:] 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.

Answer: d [Reason:] 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.

Answer: a [Reason:] 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.

Answer: a [Reason:] In continuous culture, The turn- over rate (conversion of the substance to desired product) is high and in batch culture it is less, as, Nutrients in the fermenter in batch culture is utilized in relatively slow rate compared to the continuous culture.

Answer: a [Reason:] Smaller size fermenter is required in continuous culture since the yield is very high.

Answer: c [Reason:] No such washing step is required since continuous addition of nutrients and microbes are performed.

Answer: a [Reason:] 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.

Answer: b [Reason:] 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 (Fe2+ 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.

Answer: c [Reason:] Rate of cell growth is described by the equation:

rX = μx
where rX is the volumetric rate of biomass production with units of, for example, kg m^-3 s- I, x is viable cell concentration with units of, for example, kg m^-3, and μ is the specific growth rate. Specific growth rate has dimensions T- 1.

Answer: d [Reason:] In death phase, the cells lose viability and lyse. Therefore, μ =0.

Answer: c [Reason:] In growth phase, Growth achieves its maximum rate. Therefore, μ ≈ μmax.

Answer: a [Reason:] Growth always appears much slower at the beginning of culture because the number of cells present is small.

Answer: b [Reason:] The specific growth rate of cells is dependent on the concentration of nutrients in the medium. Often, a single substrate exerts a dominant influence on rate of growth; this component is known as the growth-rate-limiting substrate or, more simply, the growth-limiting substrate. The growth-limiting substrate is often the carbon or nitrogen source, although in some cases it is oxygen or another oxidant such as nitrate.

Answer: a [Reason:] Growth for multicelluar organisms is typically measured in terms of the increase in size of a single organism, microbial growth is measured by the increase in population, either by measuring the increase in cell number or the increase in overall mass. Cell division process begins with cell elongation, which requires careful enlargement of the cell membrane and the cell wall, in addition to an increase in cell volume.

Answer: a [Reason:] The lag phase is the time period when there is no immediate increase in cell number of microorganisms as they are introduced into fresh culture medium. The microorganisms during this phase are trying to acclimatize to the new culture medium as it may be different from the previous one in which the microorganism was growing. Typically cells in the lag period are synthesizing RNA, enzymes, and essential metabolites that might be missing from their new environment (such as growth factors or macromolecules), as well as adjusting to environmental changes such as changes in temperature, pH, or oxygen availability. They can also be undertaking any necessary repair of injured cells.

Answer: a [Reason:] This is a brief transient period during which cells start growing slowly. In fact, acceleration phase connects the lag phase and log phase.

Answer: d

Answer: a [Reason:] A chemostat (from chemical environment is static) is a bioreactor to which fresh medium is continuously added, while culture liquid containing left over nutrients, metabolic end products and microorganisms are continuously removed at the same rate to keep the culture volume constant.

Answer: c [Reason:] When microbes lack the nutrients necessary for growth, they enter stationary phase. In cases when energy sources are still present in the environment, they must decide whether to continue to use their metabolic program to harvest the available energy. Here we characterized the metabolic response to a variety of types of nutrient starvation in Escherichia coli and Bacillus subtilis.

Answer: b [Reason:] During this phase bacteria divides continuously at constant rate and the number of bacteria increase exponentially. In this phase all bacteria are in their rapid stage of cell division and show balanced growth. Due to rapid cell division, bacteria have smallest size in this phase.

Answer: a [Reason:] A generation time is simply the time it takes for one cell to become two. When growing exponentially by binary fission, the increase in a bacterial population is by geometric progression. If we start with one cell, when it divides, there are 2 cells in the first generation, 4 cells in the second generation, 8 cells in the third generation, and so on. The generation time is the time interval required for the cells (or population) to divide.

Answer: a [Reason:] The growth rate can be expressed in terms of mean growth rate constant (k), the number of generations per unit time. Mean generation time or mean doubling time (g), is the time taken to double its size.

Answer: c [Reason:] A spectrophotometer optically determines the absorbance or transmission of characteristic wavelengths of radiant energy (light) by a chemical species in solution. Each molecule absorbs light at certain wavelengths in a unique spectral pattern because of the number and arrangement of its characteristic functional groups, such as double bonds between carbon atoms. According to the Beer-Lambert law, the amount of light absorbed at these wavelengths is directly proportional to the concentration of the chemical species.