MCQOPTIONS
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MCQOPTIONS
This section includes 108 Mcqs, each offering curated multiple-choice questions to sharpen your Microbiology knowledge and support exam preparation. Choose a topic below to get started.
| 1. |
The oxygen uptake requirements of a microbial population is characterized by the following parameters: μm = 0.2 h-1, K0 = 0.2 mg O2.l-1, Y0 = 0.5 mg dry weight/mg O2 and C0,crit=0.8 mg.l-1 The required concentration of cells is 1000 mg.l-1 and the saturation oxygen concentration of the medium is 5.8 mg.l-1. The required KLa must be greater than |
| A. | 64 h-1 |
| B. | 32 h-1 |
| C. | 16 h-1 |
| D. | 8h-1 |
| Answer» B. 32 h-1 | |
| 2. |
In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h-1, then the oxygen uptake will be |
| A. | 23 kg.h-1 |
| B. | less than 23 kg.h-1 |
| C. | greater than 23 kg.h-1 |
| D. | 2.3 kg.h-1 |
| Answer» B. less than 23 kg.h-1 | |
| 3. |
A fermentation system has a KLa of 3 s-1 and a C0* of 5 ppm of O2. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to |
| A. | zero |
| B. | 15 mg.l-1.s-1 |
| C. | 10 mg.l-1.s-1 |
| D. | 5 mg.l-1.s-1 |
| Answer» C. 10 mg.l-1.s-1 | |
| 4. |
A fermentation system has a KLa of 3 s-1 and a C0* of 5 ppm of O2. If the bulk liquid is saturated with oxygen then the oxygen transfer rate will be equal to |
| A. | zero |
| B. | 3 mg.l-1.s-1 |
| C. | 5 mg.l-1.s-1 |
| D. | 15 mg.l-1.s-1 |
| Answer» B. 3 mg.l-1.s-1 | |
| 5. |
The effect of increasing the stirrer speed in an unbaffled stirred tank reactor is that |
| A. | a small increase in stirrer speed will cause the liquid to enter the turbulent flow regime |
| B. | as the stirrer speed increases, the liquid will continue to circulate and then become turbulent |
| C. | as the stirrer speed increases, the liquid will continue to circulate. Eventually a vortex will form. |
| D. | A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate |
| Answer» D. A vortex will form at low stirrer speeds. As the stirrer speed increases the liquid will start to circulate | |
| 6. |
The oxygen absorption rate can be determined by |
| A. | sodium sulfite oxidation method |
| B. | dynamic gassing out technique |
| C. | direct measurement |
| D. | all of these |
| Answer» E. | |
| 7. |
Industrial paddle agitators turn at the speed of |
| A. | 20 and 150 rpm |
| B. | 150 and 300 rpm |
| C. | 400 and 800 rpm |
| D. | 1150 rpm |
| Answer» B. 150 and 300 rpm | |
| 8. |
The main function of the dimples provided in the cooling jacket is to |
| A. | increase the level of turbulence of the cooling water in the jacket |
| B. | increase the residence time of the cooling water in the jacket |
| C. | increase the cooling water-jacket wall boundary layer size |
| D. | all of the above |
| Answer» B. increase the residence time of the cooling water in the jacket | |
| 9. |
The advantage of axial flow impellers over radial flow impellers is that axial flow impellers |
| A. | provide better lift of solids |
| B. | provide high shear conditions |
| C. | provide low shear conditions |
| D. | are cheaper to build |
| Answer» B. provide high shear conditions | |
| 10. |
Axial flow impellers |
| A. | provide high shear conditions for breaking up bubbles |
| B. | provide low shear conditions and are suited for use in shear sensitive procesess |
| C. | provide direct flow towards the walls of the reactor |
| D. | none of the above |
| Answer» C. provide direct flow towards the walls of the reactor | |
| 11. |
Reynolds (Rei) number for the impeller is given by (where Di, stirrer diameter; N, stirrer speed, ρ, density of fluid and μ, viscosity of fluid) |
| A. | DiVρ/μ |
| B. | Di2Nρ/μ |
| C. | Di2Vρ/μ |
| D. | DiNρ /μ |
| Answer» C. Di2Vρ/μ | |
| 12. |
Bioreactors, where vortex is formed, another dimensionless number, __________ is useful. |
| A. | Stanton |
| B. | Rayleigh |
| C. | Bond |
| D. | Froude |
| Answer» E. | |
| 13. |
What is the effect of the concentration of dissolved salts and sugars on the oxygen transfer rate? |
| A. | The saturation concentration of oxygen in the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate |
| B. | The KLa of the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate |
| C. | The KLa of the medium increases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate |
| D. | None of the above |
| Answer» B. The KLa of the medium decreases with the concentration of dissolved salts and sugars, leading to a lower oxygen transfer rate | |
| 14. |
The Intermig impeller is |
| A. | an axial flow impeller which can be used for the culture of aerobic organisms |
| B. | directed upwards rather than towards the base of the reactor |
| C. | a fork shaped extensions to the impeller facilitate bubble break up |
| D. | All of the above |
| Answer» E. | |
| 15. |
A fermentation system has a KLa of 3 s¹ and a C0* of 5 ppm of O₂. If the bulk liquid is saturated with oxygen then the oxygen transfer rate will be equal to |
| A. | zero |
| B. | 3 mg.l¹.s¹ |
| C. | 5 mg.l¹.s¹ |
| D. | 15 mg.l¹.s¹ |
| Answer» B. 3 mg.l¹.s¹ | |
| 16. |
If the stirring speed increased from 300 to 500 rpm leads to an increase in the reaction rate by two folds. Then it may be concluded that |
| A. | the reaction was mass transfer limited at 300 rpm |
| B. | the reaction was mass transfer limited at 500 rpm |
| C. | the reaction did not involve any mass transfer step |
| D. | the movement of molecules in the reactor at 300 rpm occurred due to diffusion alone |
| Answer» B. the reaction was mass transfer limited at 500 rpm | |
| 17. |
In aerobic microorganisms cultures radial flow impellers are used because |
| A. | they provide energy efficient high turbulent mixing conditions |
| B. | they provide low shear mixing conditions |
| C. | they provide high shear mixing conditions |
| D. | they ensure that bubble size is maximized leading to high oxygen transfer rates |
| Answer» D. they ensure that bubble size is maximized leading to high oxygen transfer rates | |
| 18. |
The volume of liquid (VL) in a cylindrical reactor can be calculated from the liquid height (HL) and tank diameter (Dt) using the following equation |
| A. | VL = 4/3 x π x HL x Dt³/8 |
| B. | VL= HL x π x Dt²/4 |
| C. | VL= HL x π x Dt² |
| D. | VL = 4 x π x Dt² |
| Answer» C. VL= HL x π x Dt² | |
| 19. |
The oxygen uptake requirements of a microbial population is characterized by the following parameters: μm = 0.2 h¹, K0 = 0.2 mg O₂.l¹, Y0 = 0.5 mg dry weight/mg O₂ and C0,crit=0.8 mg.l¹ The required concentration of cells is 1000 mg.l¹ and the saturation oxygen concentration of the medium is 5.8 mg.l¹. The required KLa must be greater than |
| A. | 64 h¹ |
| B. | 32 h¹ |
| C. | 16 h¹ |
| D. | 8h¹ |
| Answer» B. 32 h¹ | |
| 20. |
Penetration theory assumes that turbulent eddies travel from the bulk of the phase to the interface where they remain constant for a constant exposure time (te). The model correlating KL, mass transfer coefficient and DAB, diffusivity can be expressed as |
| A. | KL = 2(DAB/πte)^0.25 |
| B. | KL = 2(DAB/πte)^0.5 |
| C. | KL = 2(DAB/πte)^0.75 |
| D. | KL = 2(DAB/πte) |
| Answer» C. KL = 2(DAB/πte)^0.75 | |
| 21. |
Which of the following impeller is used in situation where strong vertical currents are desirable for suspending heavily particles? |
| A. | Propeller |
| B. | Paddle |
| C. | Turbine |
| D. | None of these |
| Answer» B. Paddle | |
| 22. |
In a tall reactor, oxygen transfer rates will be |
| A. | highest at the surface of the reactor |
| B. | highest at the base of the reactor |
| C. | highest in the middle of the reactor |
| D. | the same throughout the reactor |
| Answer» C. highest in the middle of the reactor | |
| 23. |
Power number is expressed as |
| A. | P₀ / N²Di³ρ |
| B. | P₀ / N³Di⁵ρ |
| C. | P₀ / N³Di³ρ |
| D. | P₀ / N²Di²ρ |
| Answer» C. P₀ / N³Di³ρ | |
| 24. |
Surface renewal theory predicts that the mass transfer coefficient is |
| A. | directly proportional to the square root of the molecular diffusivity |
| B. | inversely proportional to the square root of the molecular diffusivity |
| C. | directly proportional to the cube root of the molecular diffusivity |
| D. | indirectly proportional to the cube root of the molecular diffusivity |
| Answer» B. inversely proportional to the square root of the molecular diffusivity | |
| 25. |
When liquid is pumped through cooling coil in a stirred tank reactor to cool. Which of the following is not correct? |
| A. | If the stirrer speed is increased, the rate will be faster |
| B. | Baffles in the tank will increase the rate of cooling |
| C. | Faster cooling rates at a slower rate of pumping |
| D. | Faster cooling rates at a faster rate of pumping |
| Answer» D. Faster cooling rates at a faster rate of pumping | |
| 26. |
Transient flow range of mixing speed is obtained for |
| A. | Rei<10 |
| B. | 10<Rei<104 |
| C. | Rei>10⁴ |
| D. | None of these |
| Answer» C. Rei>10⁴ | |
| 27. |
Why vortexing is undesirable in the agitation of biological systems? |
| A. | The collision between the cells, impeller and air bubbles will lead to cell damage |
| B. | Poor mixing despite the use of high stirrer speeds |
| C. | Mixing will not be in the turbulent region |
| D. | All of the above |
| Answer» E. | |
| 28. |
In a two-phase system where the continuous phase remains in place, the gas hold up can be expressed as (where Vs and Vt are the superficial gas velocity and bubble rise velocity) |
| A. | H = Vs/(Vs-Vt) |
| B. | H = Vs/(Vs+ Vt) |
| C. | H = Vs/(Vs.Vt) |
| D. | H = (Vs+Vt)/Vs |
| Answer» C. H = Vs/(Vs.Vt) | |
| 29. |
In the bubble boundary layer, oxygen concentration can be determined by measuring |
| A. | the steady state oxygen concentration in a mixed aerated reactor before inoculation |
| B. | the steady state oxygen concentration in a mixed aerated reactor after inoculation |
| C. | the steady state oxygen concentration in the boundary layer using a micro-probe |
| D. | volume of oxygen supplied |
| Answer» B. the steady state oxygen concentration in a mixed aerated reactor after inoculation | |
| 30. |
The average fractional gas hold up (H) can be given as (where Zf and Zl are the level of aerated and clear liquid respectively) |
| A. | H = (Zf-Zl)/Zf |
| B. | H = Zf/Zl |
| C. | H = Zf/ZfZl |
| D. | H =(Zf+Zl)/Zf |
| Answer» B. H = Zf/Zl | |
| 31. |
Power number is ratio of |
| A. | imposed forced to intertial force |
| B. | bouyant force to inertial force |
| C. | gravitation force to inertial force |
| D. | imposed force to gravitational force |
| Answer» B. bouyant force to inertial force | |
| 32. |
Which device is commonly used for measuring the rate of rotation (rpm) of the stirrer shaft? |
| A. | Anemometer |
| B. | Manometer |
| C. | Tachometer |
| D. | Barometer |
| Answer» D. Barometer | |
| 33. |
Which of the following number is calculated from the diameter and peripheral speed of the impeller? |
| A. | Reynolds number |
| B. | Froude number |
| C. | Power number |
| D. | None of these |
| Answer» B. Froude number | |
| 34. |
Laminar flow range of mixing speed is obtained for |
| A. | Rei<10 |
| B. | 10<Rei<104 |
| C. | Rei>104 |
| D. | None of these |
| Answer» B. 10<Rei<104 | |
| 35. |
What is/are the major difference(s) between disc and turbine type stirrer? |
| A. | Blades in disc type are projected out beyond the edge of disc while blades are curved one in turbine type |
| B. | Turbine type requires 50 % less air than disc type for the same yield and energy consumption |
| C. | Both (a) and (b) |
| D. | Number of blades in the stirrer |
| Answer» D. Number of blades in the stirrer | |
| 36. |
The reason of using a flat disk in a Turbine is |
| A. | to create high shear conditions |
| B. | to break up bubbles more efficiently than the impeller blades |
| C. | to ensure that the bulk of the energy consumption occurs at the blades |
| D. | all of the above |
| Answer» D. all of the above | |
| 37. |
At 25°C, the saturation concentration of oxygen in water is 1.26 mmol/l and the partial pressure of oxygen is 1 atm. The Henry's law constant will be |
| A. | 0.793atml/mmol |
| B. | 0.207atml/mmol |
| C. | 1.26 atml/mmol |
| D. | 8.74 atml/mmol |
| Answer» B. 0.207atml/mmol | |
| 38. |
In a bioreactor, if at a particular time the oxygen transfer rate is 23 kg.h¹, then the oxygen uptake will be |
| A. | 23 kg.h¹ |
| B. | less than 23 kg.h¹ |
| C. | greater than 23 kg.h¹ |
| D. | 2.3 kg.h¹ |
| Answer» B. less than 23 kg.h¹ | |
| 39. |
Which of the following type(s) of stirrer can be used for microbiological processes? |
| A. | Mig |
| B. | Intermig |
| C. | Turbine |
| D. | All of these |
| Answer» E. | |
| 40. |
Oxygen transfer rate is increased with an increase in the stirrer speed in aerated bioreactor because |
| A. | it decrease the bubble size |
| B. | it decreases the size of the boundary layer surrounding a bubble |
| C. | it increases the rate of movement of oxygen molecules through the bulk liquid |
| D. | all of the above |
| Answer» E. | |
| 41. |
For aerated mixing vessels in an aqueous solution, the mass transfer coefficient (kL) co-relating power consumption (Pm) and fermenter volume (V) can be expressed as |
| A. | kL ∝ (Pm/V)0.33 |
| B. | kL ∝ (Pm/V)0.66 |
| C. | kL ∝ (Pm/V)0.50 |
| D. | kL ∝ (Pm/V) |
| Answer» B. kL ∝ (Pm/V)0.66 | |
| 42. |
Which of the following model holds correct for the two-film theory? (where KL is the mass transfer coefficient, DAB diffusivity and Zf film thickness) |
| A. | KL = DAB/Zf |
| B. | KL = DAB |
| C. | KL = Zf/DAB |
| D. | KL = DAB.Zf |
| Answer» B. KL = DAB | |
| 43. |
Turbulent flow range of mixing speed is obtained for |
| A. | Rei<10 |
| B. | 10<Rei<10⁴ |
| C. | Rei>10⁴ |
| D. | None of these |
| Answer» D. None of these | |
| 44. |
A higher liquid height will lead to a higher gas hold up by which the oxygen transfer rate will be |
| A. | higher throughout the reactor |
| B. | lower throughout the reactor |
| C. | higher at the base of the reactor |
| D. | lower at the base of the reactor |
| Answer» D. lower at the base of the reactor | |
| 45. |
For turbulent flow, Reynolds number is correlated with power number as (where K, a constant which depends on the container geometry and shape of stirrer; Rei, is Reynolds number for agitator; Di, stirrer diameter and N, stirrer speed) |
| A. | Np = K(Rei)¹ |
| B. | Np = N2Di(Rei)¹ |
| C. | Np = K |
| D. | Can't be correlated |
| Answer» D. Can't be correlated | |
| 46. |
A fermentation system has a KLa of 3 s¹ and a C0* of 5 ppm of O₂. If the bulk liquid is completely depleted of oxygen, then the oxygen transfer rate will be equal to |
| A. | zero |
| B. | 15 mg.l¹.s¹ |
| C. | 10 mg.l¹.s¹ |
| D. | 5 mg.l¹.s¹ |
| Answer» C. 10 mg.l¹.s¹ | |
| 47. |
The power required by an agitator operating in a gas-sparged system is |
| A. | lesser than the power required by an impeller in operating at same speed in a gas free system |
| B. | more than the power required by an impeller in operating at same speed in a gas free system |
| C. | same as the power required by an impeller in operating at same speed in a gas free system |
| D. | none of the above |
| Answer» B. more than the power required by an impeller in operating at same speed in a gas free system | |
| 48. |
Which of the following impellers generate a flow parallel to the axis of shaft? |
| A. | Axial flow |
| B. | Radial flow |
| C. | Both (a)and(b) |
| D. | None of these |
| Answer» B. Radial flow | |
| 49. |
An increase in the heat transfer in the stirred tank reactor will be observed at |
| A. | higher cooling water temperature |
| B. | higher stirrer speed |
| C. | the removal of baffles from the reactor |
| D. | slower stirrer speed |
| Answer» C. the removal of baffles from the reactor | |
| 50. |
The addition of antifoams to an aerated bioreactor will decrease oxygen transfer rates because antifoams |
| A. | increase the tendency of bubbles to coalesce |
| B. | tend to accumulate in the gas liquid interface |
| C. | reduce the surface tension of the liquid |
| D. | All of the above answers |
| Answer» E. | |