Wednesday, 1 January 2020

MICRO BIOLOGY




UNIT II
2.
10. Which of the following class consists of microorganisms which are not causative agents?
a) EFB Class 1
b) EFB Class 2
c) EFB Class 3
d) EFB Class 4
View Answer
Answer: a
Explanation: Microorganisms that have never been identified as causative agents of disease in man are termed as harmless microorganisms and belong to EFB Class 1 and do not offer a threat to the environment.
11. Which of the following class consists of microorganisms which are causing disease in man and are hazardous to workers?
a) EFB Class 3
b) EFB Class 1
c) EFB Class 2
d) EFB Class 4
View Answer
Answer: c
Explanation: Microorganisms that may cause disease in man and are, therefore, hazardous to laboratory workers. They do not spread in the environment. Prophylactics are used for the treatment. They are called as low-risk microorganisms.
12. EFB Class 4 consists of ___________
a) Low-risk microorganisms
b) High-risk microorganisms
c) Medium-risk microorganisms
d) Environmental-risk microorganisms
View Answer
Answer: b
Explanation: EFB Class 4 consists of High-risk microorganisms. These are microorganisms which cause severe illness to the microorganisms and are very hazardous to people at work. No effective treatment is available for this class.
13. Which of the following class of microorganisms causes less threat to a man?
a) Low-risk microorganisms
b) High-risk microorganisms
c) Medium-risk microorganisms
d) Environmental-risk microorganisms
View Answer
Answer: d
Explanation: Microorganisms which cause less threat to man and are very hazardous to the environment. They are also called as environmental-risk microorganisms and are responsible for high economic losses.
1. The smaller bubbles are sensitive than larger bubbles?
a) True
b) False
View Answer
Answer: a
Explanation: kL in fermentation liquids is about 3-4×10-4 m s-1 for bubbles greater than 2-3 mm diameter; this can be reduced to 1×10-4m s-1 for smaller bubbles depending on bubble rigidity. Once the bubbles are above 2-3 mm in size, kL is relatively constant and insensitive to conditions.
2. Which size of bubbles is relevant for mass transfer?
a) Small
b) Very small
c) Large
d) Very large
View Answer
Answer: a
Explanation: The most important property of air bubbles in fermenters is their size. Small bubbles have correspondingly slow bubble-rise velocities; consequently they stay in the liquid longer, allowing more time for the oxygen to dissolve. While it is desirable to have small bubbles, there are practical limits. Bubbles << 1 mm diameter can become a nuisance in bioreactors. Oxygen concentration in these bubbles equilibrates with that in the medium within seconds, so that the gas hold-up no longer reflects the capacity of the system for mass transfer.
3. Coalescence is appropriate for oxygen transfer in bubbles?
a) True
b) False
View Answer
Answer: b
Explanation: Coalescence of small bubbles into bigger bubbles is generally undesirable because it reduces the total interfacial area and gas hold-up. Frequency of coalescence depends mainly on the liquid properties. In a coalescing liquid, a large fraction of bubble collisions results in the formation of bigger bubbles, while in non-coalescing liquids colliding bubbles do not coalesce readily. Salts act to suppress coalescence; therefore, fermentation media are usually non-coalescing to some extent depending on com- position. This is an advantage for oxygen mass transfer.
4. What do you mean by “Impeller flooding”?
a) The flooding of an impeller
b) Gas handling is greater than the amount introduced
c) Gas handling is smaller than the amount introduced
d) Leakage of the Broth
View Answer
Answer: c
Explanation: Impeller flooding is said to occur; this means that the gas-handling capacity of the stirrer is smaller than the amount introduced. Flooding should be avoided because an impeller surrounded by gas no longer contacts the liquid properly, resulting in poor mixing and gas dispersion.
5. Dispersion of gas in stirred vessels is largely independent of sparger design?
a) True
b) False
View Answer
Answer: a
Explanation: In a non-coalescing liquid, the bubbles remain close to the size produced at the back of the cavities. Because bubbles formed at the sparger are immediately drawn into the impeller zone, dispersion of gas in stirred vessels is largely independent of sparger design; when the sparger is located under the stirrer, it has been shown that sparger type does not significantly affect mass transfer.
6. Which of the following is not an antifoam agent?
a) Surfactants
b) Silicone oil
c) Fluorosilicone
d) Fatty alcohol
View Answer
Answer: a
Explanation: A foaming agent is a material that facilitates formation of foam such as a surfactant or a blowing agent. A surfactant, when present in small amounts, reduces surface tension of a liquid (reduces the work needed to create the foam) or increases its colloidal stability by inhibiting coalescence of bubbles.
7. Which type of fermenter is used in laboratory scale?
a) Stirred tanks
b) Shake-flask
c) Bubble columns
d) Air-lift fermenter
View Answer
Answer: b
Explanation: At laboratory-scale cultures may be aerated by means of the shake-flask technique where the culture is grown in a conical flask shaken on a platform contained in a controlled environment of chamber.
8. Which part of fermenter is used for mixing process?
a) Impeller
b) Shaft
c) Sparger
d) Headspace
View Answer
Answer: a
Explanation: An impeller is a rotating component of a centrifugal pump which transfers energy from the motor that drives the pump to the fluid being pumped by accelerating the fluid outwards from the center of rotation. This is how mixing is accomplished.
9. Bubble column reactor cannot be used for?
a) Low viscous medium
b) High viscous medium
c) Liquid state medium
d) Solid state medium
View Answer
Answer: b
Explanation: Bubble column reactor cannot be used for highly viscous medium. Pattern of gas bubbles in a bubble column reactor is dependent on the gas superficial velocity. Gas velocity should be 1-4 cm per second for uniform bubbles throughout medium which will provide proper mixing. If gas velocity is higher or lower than uniform bubbles will not be produced, thus when bubbles coalesce produces differences in fluid density which will disturb air flow rate.



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