Bioprocess Engineering Questions and Answers – Sterilisation

This set of Bioprocess Engineering Multiple Choice Questions & Answers (MCQs) focuses on “Sterilisation”.

1. What do you mean by “Axenic culture”?
a) Containing single type of organism
b) Containing two types of organism
c) Containing multiple types of organism
d) Not containing any type of organism
View Answer

Answer: a
Explanation: In biology, axenic describes the state of a culture in which only a single species, variety, or strain of organism is present and entirely free of all other contaminating organisms. Axenic culture is also an important tool for the study of symbiotic and parasitic organisms in a controlled manner.

2. Cell death in solids is more effective than liquid.
a) True
b) False
View Answer

Answer: b
Explanation: If the liquid contains contaminant particles in the form of flocs or pellets, temperature gradients may develop. Because heat transfer within solid particles is slower than in liquid, the temperature at the centre of the solid will be lower than that in the liquid for some proportion of the sterilising time. As a result, cell death inside the particles is not as effective as in the liquid. Longer holding times are required to treat solid-phase substrates and media containing particles.

3. Hold-up of large volumes of medium for longer periods of time is efficient.
a) True
b) False
View Answer

Answer: a
Explanation: Sustained elevated temperatures during heating and cooling are damaging to vitamins, proteins and sugars in nutrient solutions and reduce the quality of the medium. Because it is necessary to hold large volumes of medium for longer periods of time. Continuous sterilisation, particularly a high-temperature, short-exposure-time process, can significantly reduce damage to medium ingredients while achieving high levels of cell destruction.
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4. Plug flow contains _______________
a) There is mixing
b) There is variation
c) There is no mixing but variation
d) There is neither mixing nor variation
View Answer

Answer: d
Explanation: The type of flow in pipes where there is neither mixing nor variation in fluid velocity is called Plugflow. Plug flow is an ideal flow pattern; in reality, fluid elements in pipes have a range of different velocities.

5. For an ideal plug flow, Reynolds number should be ____________
a) Low
b) Variably low
c) High
d) Not very high
View Answer

Answer: c
Explanation: Plug flow is approached in pipes at turbulent Reynolds numbers above about 2 × 104; operation at high Reynolds numbers minimises fluid mixing and velocity variation.
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6. Deviation from plug flow behavior is ____________
a) Linear dipersion
b) Axial dispersion
c) Circular dispersion
d) Non-dispersion
View Answer

Answer: b
Explanation: Deviation from plug-flow behaviour is characterised by the degree of axial dispersion in the system, i.e. the degree to which mixing occurs along the length or axis of the pipe. Axial dispersion is a critical factor affecting design of continuous sterilisers.

7. Peclet number has no units.
a) True
b) False
View Answer

Answer: a
Explanation: The Peclet number is a dimensionless number used in calculations involving convective heat transfer. It is the ratio of the thermal energy convected to the fluid to the thermal energy conducted within the fluid.
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8. Performance of sterilizer is directly proportional to the Peclet number.
a) True
b) False
View Answer

Answer: a
Explanation: At any given sterilisation temperature defining the value of kd and Da, performance of the steriliser declines significantly as the Peclet number decreases.

9. The pores of filter for filtration should be between in diameter is _________
a) 0.1 – 0.55 μm
b) 0.2 – 0.45 μm
c) 0.3 – 0.45 μm
d) 0.3 – 0.50 μm
View Answer

Answer: b
Explanation: Membranes used for filter sterilisation of liquids are made of cellulose esters or other polymers and have pores between 0.2 and 0.45 μm in diameter. The membranes themselves must be sterilised before use, usually by steam.
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10. Heat sterilization is more effective than filtration for liquid medium.
a) True
b) False
View Answer

Answer: a
Explanation: Liquid filtration is generally not as effective or reliable as heat sterilisation. Viruses and mycoplasma are able to pass through membrane filters; care must also be taken to prevent holes or tears in the membrane. Usually, filter-sterilised medium is incubated for a period of time before use to test its sterility.

11. Membrane filters and depth filters are same.
a) True
b) False
View Answer

Answer: b
Explanation: A Depth Filter is a filter consisting of either multiple layers or a single layer of a medium having depth, which captures contaminants within its structure, as opposed to on the surface. Depth filters typically have nominal pore size ratings, Whereas, Membrane filters or “membranes” are microporous plastic films with specific pore size ratings. Also known as screen, sieve or microporous filters, membranes retain particles or microorganisms larger than their pore size primarily by surface capture.

12. Membrane filters are more efficient than depth filters.
a) True
b) False
View Answer

Answer: a
Explanation: Depth filters do not perform well if there are large fluctuations in flow rate or if the air is wet; liquid condensing in the filter increases the pressure drop, causes channelling of the gas flow, and provides a pathway for organisms to grow through the bed, Whereas, Membrane filter cartridges typically contain a pleated, hydrophobic filter with small and uniformly-sized pores 0.45 pm or less in diameter. The hydrophobic nature of the surface minimises problems with filter wetting while the pleated configuration allows a high filtration area to be packed into a small cartridge volume.

13. Deep bed filters are used for filtration of?
a) Liquid
b) Solid
c) Gas
d) Non-fluid
View Answer

Answer: a
Explanation: Deep bed filtration is a rapid and efficient method for removing small particles from liquids. Such dispersions of particles in liquids are common in a wide range of industries.

14. 20-micron filter is more efficient than 5-micron filter.
a) True
b) False
View Answer

Answer: b
Explanation: The average size of the openings between pieces of the filter media are represented in microns. For example, a 20-micron filter has larger openings than a 5-micron filter. Consequently, the 20-micron filter element will let larger particles pass through the filter than the 5-micron media would.

15. What is an MPR rating on air filters?
a) Magnitude performance rating
b) Micro-particle performance rating
c) Macro-particle performance rating
d) Moles per rate
View Answer

Answer: b
Explanation: MPR (Micro-Particle Performance Rating) MPR Rating is a rating system developed by 3M. It rates the manufacturer’s filters and their ability to capture airborne particles smaller than 1 micron.

Sanfoundry Global Education & Learning Series – Bioprocess Engineering.

To practice all areas of Bioprocess Engineering, here is complete set of 1000+ Multiple Choice Questions and Answers.

If you find a mistake in question / option / answer, kindly take a screenshot and email to [email protected]

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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