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Bioprocess Engineering Multiple Choice Questions on “Monitoring and Control of Bioreactors”.
1. In-situ or on-line measurement is appropriate for biomass analysis in fermentation.
A. True
B. False
Answer: B
Explanation: Many important variables such as biomass concentration and broth composition cannot currently be measured on-line because of the lack of appropriate instruments. Instead, samples must be removed from the reactor and taken to the laboratory for off-line analysis. Because fermentation conditions can change during laboratory analysis, control action based on the measurement is not as effective. Off-line measurements are used in industrial fermentations for analysis of biomass, carbohydrate, protein, phosphate and lipid concentrations, enzyme activity and broth rheology. Samples are usually taken manually every 4-8 h; the results are available 2-24 h later.
2. What do you mean by dissolved oxygen tension?
A. Force
B. Density
C. Partial pressure
D. Volume
Answer: C
Explanation: The partial pressure of oxygen molecules dissolved in a liquid, such as blood plasma. Technically the oxygen tension (or partial pressure of oxygen) is defined as the pressure which oxygen in a mixture of gases would exert if it were on its own. Weirdly, partial pressures/gas tensions are also used to describe dissolved gases, in the blood for example.
3. Which electronic device is used in biosensors?
A. Transmitter
B. Receptor
C. Transducer
D. Electrolyte
Answer: C
Explanation: The preferred biological material like enzyme is preferred for conventional methods like physical or membrane entrapment and non covalent or covalent binding. The preferred biological material is in contact with the transducer. To produce a bound analyte through the analyte binds to the biological material which produces the electrical response to be measured. In some cases the analyte changed to a product and have some probability to associate with the release of heat, gases like oxygen, electrons or hydrogen ions.
4. Flow injection analysis (FIA), a sampling handling technique is used to remove?
A. Analyte
B. Electrolyte
C. Cell-free medium
D. Cell-bound medium
Answer: C
Explanation: The flow injection analysis (FIA), a sample-handling technique for removing cell- free medium from the fermenter and delivering a pulse of analyte to ex situ measurement devices.
5. What is the unit of Specific Oxygen rate (SOUR)?
A. grams of oxygen consumed per gram of volatile suspended solids per hour
B. milligrams of oxygen consumed per gram of volatile suspended solids per hour
C. kilograms of oxygen consumed per gram of volatile suspended solids per second
D. milligrams of oxygen consumed per gram of volatile suspended solids per second
Answer: B
Explanation: The Specific Oxygen Uptake Rate (SOUR), also known as the oxygen consumption or respiration rate, is defined as the milligram of oxygen consumed per gram of volatile suspended solids (VSS) per hour. This quick test has many advantages; rapid measure of influent organic load and biodegradability, indication of the presence of toxic or inhibitory wastes, degree of stability and condition of a sample, and calculation of oxygen demand rates at various points in the aeration basin.
6. In process modeling, experimental observations provide:
A. Structure of the model
B. Non-numerical values of coefficients
C. Non-numerical values of variables
D. Numerical values of coefficients
Answer: D
Explanation: Traditionally, models are based on a combination of ‘theoretical’ relationships which provide the structure of the model, and experimental observations which provide the numerical values of coefficients. For biological processes, specifying the model structure can be difficult because of the complexity of cellular processes and the large number of environmental factors which affect cell culture. Usually, bioprocess models are much-simplified approximate representations deduced from observation rather than from theoretical laws of science. As an example, a frequently-used mathematical model for batch fermentation consists of the Monod equation for growth and an expression for rate of substrate consumption as a function of biomass concentration.
7. Accurate models applicable to a range of process conditions are not rare.
A. True
B. False
Answer: B
Explanation: Development of a comprehensive model covering all key aspects of a particular bioprocess and able to predict the effects of a wide range of culture variables is a demanding exercise. Accurate models applicable to a range of process conditions are rare. As many aspects of fermentation are poorly under- stood, it difficult to devise mathematical models covering these areas. For example, the response of cells to spatial variations in dissolved-oxygen and substrate levels in fermenters, or the effect of impeller design on microbial growth and productivity, is not generally incorporated into models because the subject has been inadequately studied.
8. What is the Kalman filter?
A. Algorithm
B. Computer device
C. Filtration equipment
D. Constant measurement device
Answer: A
Explanation: Kalman filtering, also known as linear quadratic estimation (LQE), is an algorithm that uses a series of measurements observed over time, containing statistical noise and other inaccuracies, and produces estimates of unknown variables that tend to be more accurate than those based on a single measurement alone, by estimating a joint probability distribution over the variables for each timeframe.
9. The actuator converts the energy into mechanical action.
A. True
B. False
Answer: A
Explanation: An actuator is a type of motor that is responsible for moving or controlling a mechanism or system. It is operated by a source of energy, typically electric current, hydraulic fluid pressure, or pneumatic pressure, and converts that energy into motion.
10. What is proportional-integral-derivative (PID)?
A. Bioreactor
B. Controller
C. Mathematical integration
D. Mathematical differentiation
Answer: B
Explanation: The proportional-integral-derivative or PID control, with PID control, the control action is determined in proportion to the error, the integral of the error and the derivative of the error with respect to time. The relative weightings given to these functions determine the response of the controller and the overall ‘strength’ of the control action.
11. PID controllers can affect the culture medium.
A. True
B. False
Answer: A
Explanation: Proper adjustment of PID controllers usually provides excellent regulation of the measured variable. However, poorly tuned controllers can de stabilize a process and cause continuous or accentuated fluctuations in culture conditions.
12. Respiratory quotient has no units.
A. True
B. False
Answer: A
Explanation: The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. It is calculated from the ratio of carbon dioxide produced by the body to oxygen consumed by the body. Such measurements, like measurements of oxygen uptake, are forms of indirect calorimetry.
13. Biomass yield from substrate and fermentative metabolism are same.
A. True
B. False
Answer: B
Explanation: Maximum biomass yield from substrate is achieved at relatively low glucose concentrations in the presence of adequate oxygen; fermentative metabolism occurs if the glucose concentration rises above a certain level even though oxygen may be present. Fermentative metabolism should be avoided for biomass production because the yield of cells is reduced as ethanol and carbon dioxide are formed as end-products.
14. Crabtree effect is which type of process?
A. Aerobic
B. Anaerobic
C. Biomass yield
D. Oxidative phosphorylation
Answer: A
Explanation: The Crabtree effect describes the phenomenon whereby the yeast, Saccharomyces cerevisiae, produces ethanol (alcohol) in aerobic conditions and high external glucose concentrations rather than producing biomass via the tricarboxylic acid (TCA. cycle, the usual process occurring aerobically in most yeasts e.g. Kluyveromyces spp. Increasing concentrations of glucose accelerates glycolysis (the breakdown of glucose) which results in the production of appreciable amounts of ATP through substrate-level phosphorylation. This reduces the need of oxidative phosphorylation done by the TCA cycle via the electron transport chain and therefore decreases oxygen consumption.
15. Neural network process includes ___________
A. Constant behavior
B. Transient behavior
C. Stationary behavior
D. Immobile behavior
Answer: B
Explanation: Information about feed flow rate and substrate and biomass concentrations as a function of time can be used to develop a neural network for analysis of transient behaviour in continuous fermentation which is able to predict future changes in substrate and cell concentrations.