Here are the 100 MCQs for Part 3: Physical Sterilization:

Basic Concepts and Definitions

1. Sterilization is defined as:

• a) The removal of vegetative pathogens only

• b) The complete removal or destruction of all living microorganisms, including spores

• c) Reduction of microbial contamination to safe levels

• d) Inhibition of microbial growth

Answer: b

2. Which of the following is a sterilizing agent?

• a) Ethanol

• b) Formaldehyde

• c) Sterilant

• d) Phenol

Answer: c

3. The term “commercial sterilization” refers to:

• a) The complete removal of all microbes in food products

• b) Heat treatment sufficient to destroy Clostridium botulinum spores in canned foods

• c) Disinfection of surfaces used in food production

• d) Pasteurization of beverages

Answer: b

Heat-Based Sterilization

4. The most practical and efficient method of sterilization for heat-resistant materials is:

• a) Dry heat
• b) Moist heat

• c) Filtration

• d) Radiation

Answer: b

5. Which of the following statements about autoclaving is correct?

• a) It uses dry heat to sterilize materials.

• b) It destroys all microorganisms, including bacterial spores, at 121°C and 15 psi for 15
minutes.

• c) It is not suitable for sterilizing surgical instruments.

• d) It cannot sterilize liquids.

Answer: b

6. Pasteurization is used to:

• a) Sterilize milk and other beverages

• b) Reduce microbial load without destroying all microbes

• c) Kill bacterial spores

• d) Achieve complete sterility

Answer: b

7. The high-temperature short-time (HTST) pasteurization method involves heating at:

• a) 63°C for 30 minutes

• b) 72°C for 15 seconds

• c) 100°C for 1 hour

• d) 140°C for 4 seconds

Answer: b

8. Which of the following organisms is the primary target for destruction in pasteurization?
• a) Escherichia coli

• b) Mycobacterium tuberculosis

• c) Bacillus anthracis

• d) Staphylococcus aureus

Answer: b

Dry Heat Sterilization

9. Dry heat sterilization kills microorganisms by:

• a) Coagulating proteins

• b) Oxidizing cellular components

• c) Disrupting the cell membrane

• d) Inhibiting DNA replication

Answer: b

10. The minimum temperature and time for dry heat sterilization in an oven are:

• a) 100°C for 30 minutes

• b) 121°C for 15 minutes

• c) 160°C for 2 hours

• d) 200°C for 10 minutes

Answer: c

11. Which method uses an open flame to sterilize tools like inoculation loops?

• a) Autoclaving

• b) Incineration

• c) Dry heat oven

• d) Radiation
Answer: b

Radiation-Based Sterilization

12. UV light sterilization works by:

• a) Generating heat to destroy cells

• b) Causing thymine dimers in DNA

• c) Oxidizing cellular components

• d) Disrupting cell membranes

Answer: b

13. Gamma rays sterilize by:

• a) Breaking hydrogen bonds

• b) Inducing free radical formation

• c) Coagulating proteins

• d) Altering pH

Answer: b

14. Which of the following is a disadvantage of UV light sterilization?

• a) Limited penetration ability

• b) Production of toxic byproducts

• c) Ineffectiveness against spores

• d) High cost

Answer: a

Filtration

15. Filtration is used to sterilize:

• a) Heat-sensitive liquids and gases

• b) Surgical instruments

• c) Metallic equipment

• d) Glassware

Answer: a

16. Membrane filters typically used in filtration sterilization have a pore size of:

• a) 10 microns

• b) 1 micron

• c) 0.45 microns

• d) 0.22 microns

Answer: d

17. Which of the following microorganisms might pass through a 0.22-micron filter?

• a) Gram-positive bacteria

• b) Gram-negative bacteria

• c) Mycoplasma

• d) Endospores

Answer: c

Sterilization Techniques and Applications

18. The sterilization method of choice for media and glassware is:

• a) Autoclaving

• b) Filtration

• c) Pasteurization

• d) Dry heat

Answer: a
19. Incineration is primarily used for:

• a) Sterilizing culture media

• b) Destroying disposable medical waste

• c) Disinfecting surgical instruments

• d) Preserving bacterial cultures

Answer: b

20. Which physical method is most effective in sterilizing heat-sensitive items such as
plastic syringes?

• a) Dry heat

• b) Filtration

• c) Gamma radiation

• d) UV radiation

Answer: c

Effectiveness and Limitations

21. The effectiveness of heat sterilization depends on:

• a) Temperature and time

• b) The presence of moisture

• c) Microbial load

• d) All of the above

Answer: d

22. The thermal death point (TDP) is defined as:

• a) The time required to kill all microbes at a given temperature

• b) The lowest temperature at which all microbes are killed in 10 minutes

• c) The time to kill 90% of microbes

• d) The time required to kill all spores

Answer: b

23. The D-value in sterilization refers to:

• a) The time required to kill 90% of microorganisms at a specific temperature

• b) The lowest temperature to kill all microbes

• c) The time required to sterilize an object

• d) The destruction of bacterial endospores

Answer: a

Part 3: Physical Sterilization (Continued)

Moist Heat Sterilization

24. The principle of moist heat sterilization involves:

• a) Oxidation of cellular components

• b) Protein denaturation and coagulation

• c) Dehydration of microorganisms

• d) Alteration of DNA synthesis

Answer: b

25. Which of the following materials can be sterilized using an autoclave?

• a) Culture media

• b) Surgical instruments

• c) Glassware

• d) All of the above

Answer: d
26. Which physical factor enhances the killing power of moist heat?

• a) Low pressure

• b) High pressure

• c) Dry environment

• d) Increased oxygen levels

Answer: b

Dry Heat Sterilization

27. Flaming is a method of sterilization commonly used for:

• a) Surgical tools

• b) Metal forceps and loops

• c) Glass bottles

• d) Cotton swabs

Answer: b

28. Which of the following is an advantage of dry heat sterilization?

• a) Suitable for oils and powders

• b) Faster than moist heat sterilization

• c) Less energy consumption

• d) Effective at low temperatures

Answer: a

29. A limitation of dry heat sterilization is:

• a) Limited penetration of heat

• b) Risk of corrosion

• c) Long exposure time required

• d) Limited application to glassware

Answer: c

Pasteurization

30. The ultra-high-temperature (UHT) method of pasteurization involves:

• a) 63°C for 30 minutes

• b) 72°C for 15 seconds

• c) 140°C for 4 seconds

• d) 160°C for 10 minutes

Answer: c

31. Pasteurization reduces microbial numbers but does not:

• a) Preserve food

• b) Kill pathogens

• c) Destroy heat-resistant microbes

• d) Alter the taste of beverages

Answer: c

32. What was the historical goal of pasteurization developed by Louis Pasteur?

• a) Complete sterilization of milk

• b) Destruction of Mycobacterium tuberculosis in milk and wine

• c) Killing thermophilic bacteria in beverages

• d) Preventing yeast fermentation in wine

Answer: b

Filtration

33. Filtration is ineffective against which of the following?

• a) Viruses

• b) Bacterial spores

• c) Mycobacteria

• d) Both a and b

Answer: d

34. Which of the following filters is commonly used for air sterilization in hospitals?

• a) Membrane filters

• b) HEPA filters

• c) Depth filters

• d) Carbon filters

Answer: b

35. HEPA filters are designed to remove particles as small as:

• a) 1 micron

• b) 0.5 microns

• c) 0.3 microns

• d) 0.1 microns

Answer: c

Radiation

36. Ionizing radiation sterilizes by:

• a) Damaging microbial DNA and producing free radicals

• b) Coagulating microbial proteins

• c) Causing dehydration of cells

• d) Producing heat to kill microbes

Answer: a

37. Which of the following is an example of non-ionizing radiation?

• a) Gamma rays

• b) X-rays

• c) UV light

• d) Beta rays

Answer: c

38. UV light is most effective at a wavelength of:

• a) 100–150 nm

• b) 200–280 nm

• c) 300–350 nm

• d) 400–450 nm

Answer: b

39. A limitation of using UV light as a sterilization method is:

• a) It can only be used for liquids

• b) It cannot penetrate surfaces or opaque materials

• c) It generates toxic byproducts

• d) It is highly expensive

Answer: b

Sterilization Effectiveness

40. The time required to kill all microorganisms at a specific temperature is referred to as:

• a) Thermal death point

• b) D-value
• c) Thermal death time

• d) Sterilization time

Answer: c

41. The Z-value in sterilization is defined as:

• a) The time required to kill 90% of microbes

• b) The temperature increase needed to reduce the D-value by one log

• c) The lowest temperature to kill all microbes

• d) The sterilization rate constant

Answer: b

42. Which factors determine the effectiveness of sterilization?

• a) Nature of the material

• b) Microbial load

• c) Temperature and exposure time

• d) All of the above

Answer: d

Special Techniques

43. Freeze-drying (lyophilization) is primarily used to:

• a) Sterilize surgical instruments

• b) Preserve bacterial cultures for long-term storage

• c) Destroy bacterial spores

• d) Disinfect glassware

Answer: b

44. Ultrasonic waves are used in sterilization for:

• a) Killing bacterial spores

• b) Cleaning delicate medical instruments

• c) Sterilizing liquids

• d) Disinfecting air

Answer: b

45. What is the role of oxygen in gas gangrene treatment?

• a) It prevents anaerobic bacterial growth

• b) It sterilizes surgical wounds

• c) It denatures microbial enzymes

• d) It removes toxins from wounds

Answer: a

Clinical Applications

46. In hospitals, autoclaves are most commonly used to sterilize:

• a) Food and beverages

• b) Heat-sensitive drugs

• c) Surgical tools and dressings

• d) Plastic syringes

Answer: c

47. What type of sterilization is typically used for disposable medical equipment?

• a) Dry heat

• b) Gamma radiation

• c) Autoclaving

• d) Chemical sterilization
Answer: b

48. For sterilizing thermosensitive materials such as enzymes, which method is preferred?

• a) Filtration

• b) Pasteurization

• c) Autoclaving

• d) UV radiation

Answer: a

Part 3: Physical Sterilization (Continued)

Autoclaving

49. Which of the following substances is least affected by autoclaving?

• a) Heat-resistant bacterial spores

• b) Non-sporulating bacteria

• c) Viruses

• d) Fungi

Answer: a

50. To ensure sterilization, autoclaves are often equipped with:

• a) UV lamps

• b) Pressure gauges and biological indicators

• c) Cooling chambers

• d) Gamma-ray detectors

Answer: b

51. Which of the following can affect the efficiency of autoclaving?

• a) Volume of materials being sterilized

• b) Presence of organic matter

• c) Type of packaging material

• d) All of the above

Answer: d

52. Autoclaving is unsuitable for sterilizing:

• a) Surgical instruments

• b) Heat-labile substances

• c) Glassware

• d) Culture media

Answer: b

Pasteurization

53. Which of the following is a significant advantage of pasteurization over sterilization?

• a) Preservation of taste and nutritional quality in foods

• b) Killing all microbial forms, including spores

• c) Longer storage duration

• d) Complete microbial elimination

Answer: a

54. The difference between HTST and UHT pasteurization is primarily in:

• a) Target organisms

• b) Nutritional impact

• c) Temperature and exposure time

• d) The use of pressure

Answer: c

55. Which beverage is most commonly pasteurized using UHT methods?

• a) Beer

• b) Milk

• c) Juice

• d) Wine

Answer: b

Radiation

56. Ionizing radiation is suitable for sterilizing:

• a) Liquids and solutions

• b) Powders, plastics, and syringes

• c) Glassware and metal tools

• d) Surfaces in hospital operating rooms

Answer: b

57. UV light sterilization is most effective for:

• a) Surgical instruments

• b) Transparent fluids

• c) Disinfecting surfaces and air

• d) Heat-sensitive materials

Answer: c

58. Gamma radiation sterilizes materials by:

• a) Causing thymine dimer formation

• b) Producing free radicals and breaking DNA strands

• c) Oxidizing microbial lipids

• d) Increasing the temperature of the object

Answer: b

59. UV radiation is particularly useful for sterilizing:

• a) Food packaging materials

• b) Hospital linens

• c) Operating room air and surfaces

• d) Pharmaceuticals in solution

Answer: c

Filtration

60. Which type of filter is preferred for sterilizing large volumes of liquids?

• a) Depth filters

• b) Membrane filters

• c) HEPA filters

• d) Sand filters

Answer: b

61. HEPA filters are primarily used in:

• a) Filtration of liquids

• b) Sterilization of medical instruments

• c) Air sterilization in clean rooms and hospitals

• d) Food industry sterilization

Answer: c

62. Why are filters with a pore size of 0.22 microns commonly used?
• a) They remove all microbes, including spores

• b) They are effective against most bacteria but allow viruses to pass

• c) They destroy microbes chemically

• d) They remove larger particles but not microbes

Answer: b

Thermal Death

63. The term “thermal death time” refers to:

• a) The time needed to kill all microbes at a constant temperature

• b) The lowest temperature required to kill all microbes in 10 minutes

• c) The time needed to reduce microbial count by 90%

• d) The point at which microbial growth is completely inhibited

Answer: a

64. Why is thermal death time important in sterilization?

• a) To calculate the energy consumption of sterilization equipment

• b) To determine the effectiveness of a sterilization process

• c) To assess the pH of the material being sterilized

• d) To control microbial mutations

Answer: b

Sterilization Applications

65. Desiccation is used for:

• a) Destroying microbial spores

• b) Preserving microbial cultures by removing water

• c) Sterilizing surgical instruments

• d) Killing pathogens on surfaces

Answer: b

66. Which of the following sterilization methods is used to prevent microbial growth in
vaccines?

• a) Dry heat

• b) Filtration

• c) Pasteurization

• d) Gamma radiation

Answer: b

67. Hyperbaric oxygen therapy is used in sterilization by:

• a) Disrupting microbial DNA

• b) Enhancing oxygen delivery to anaerobic environments

• c) Increasing heat sterilization efficiency

• d) Reducing microbial metabolic activity

Answer: b

68. Which of the following is best for sterilizing heat-sensitive surgical instruments?

• a) Ethylene oxide gas

• b) Dry heat

• c) Autoclaving

• d) Incineration

Answer: a

Factors Affecting Sterilization

69. What is the effect of organic matter on sterilization?

• a) Enhances the efficiency of sterilization

• b) Protects microorganisms from the sterilization process

• c) Reduces the pH of the material being sterilized

• d) Speeds up microbial destruction

Answer: b

70. Which two factors determine the efficiency of heat sterilization?

• a) Time and microbial load

• b) Temperature and exposure time

• c) Pressure and moisture

• d) Surface area and volume

Answer: b

71. The effectiveness of chemical disinfectants can be reduced by:

• a) High temperature

• b) Low microbial load

• c) Organic debris on the surface

• d) Acidic conditions

Answer: c

Specialized Techniques

72. Ultrasonic cleaners are primarily used for:

• a) Sterilizing surgical instruments

• b) Cleaning delicate medical equipment by dislodging debris

• c) Sterilizing air and surfaces in hospitals

• d) Destroying bacterial spores

Answer: b
73. Which sterilization method is often used for plastic materials like syringes?

• a) Filtration

• b) Gamma radiation

• c) Autoclaving

• d) UV radiation

Answer: b

Part 3: Physical Sterilization (Continued)

Moist Heat Sterilization

74. In moist heat sterilization, the effectiveness of killing microorganisms depends on:

• a) Dehydration of bacterial cells

• b) Coagulation of proteins and destruction of membranes

• c) Oxidation of cellular components

• d) Disruption of DNA synthesis

Answer: b

75. Which of the following substances cannot be effectively sterilized by boiling?

• a) Non-sporulating bacteria

• b) Viruses

• c) Bacterial spores

• d) Fungi

Answer: c

76. What is the primary advantage of moist heat sterilization over dry heat?

• a) Shorter exposure times

• b) Ability to sterilize oils and powders

• c) Lower temperatures required

• d) Both a and c

Answer: d

Radiation Sterilization

77. Gamma radiation is most suitable for sterilizing:

• a) Glassware

• b) Pharmaceuticals

• c) Heat-sensitive medical supplies

• d) Bacterial cultures

Answer: c

78. What type of microorganisms are highly resistant to UV radiation?

• a) Gram-negative bacteria

• b) Fungal spores

• c) Bacterial spores

• d) Protozoa

Answer: c

79. Which of the following materials is best sterilized using ionizing radiation?

• a) Metal surgical tools

• b) Heat-labile materials like plastics

• c) Cotton swabs

• d) Autoclavable liquids

Answer: b
Filtration and Sterile Air

80. Which property of filters determines their ability to sterilize?

• a) Thickness of the filter material

• b) Pore size of the filter

• c) The material used in the filter

• d) Shape of the filter

Answer: b

81. In air sterilization, HEPA filters are used because they:

• a) Destroy microbial DNA

• b) Remove 99.97% of airborne particles larger than 0.3 microns

• c) Neutralize microbial toxins

• d) Generate ozone for disinfection

Answer: b

82. Filtration is ineffective for sterilizing:

• a) Gases

• b) Viruses smaller than the filter pore size

• c) Heat-sensitive liquids

• d) Protein-based solutions

Answer: b

Sterilization Indicators

83. Biological indicators for autoclave effectiveness typically use:

• a) Bacillus subtilis spores

• b) Geobacillus stearothermophilus spores

• c) Mycobacterium tuberculosis spores

• d) Escherichia coli cultures

Answer: b

84. What is the purpose of chemical indicators in sterilization?

• a) Confirm complete microbial destruction

• b) Measure the time required for sterilization

• c) Indicate exposure to sterilization conditions (e.g., heat, steam)

• d) Test for the presence of bacterial toxins

Answer: c

85. A biological indicator that remains viable after sterilization indicates:

• a) Complete sterilization

• b) The need to repeat the sterilization cycle

• c) Partial sterilization

• d) Inadequate disinfection

Answer: b

Sterilization in Healthcare Settings

86. Which sterilization method is commonly used for endoscopes?

• a) Dry heat

• b) Ethylene oxide gas

• c) Autoclaving

• d) UV radiation

Answer: b

87. The sterilization method of choice for heat-sensitive surgical implants is:
• a) Steam sterilization

• b) Gamma radiation

• c) Filtration

• d) Pasteurization

Answer: b

88. Operating rooms are typically disinfected using:

• a) UV light and surface disinfectants

• b) Autoclaves

• c) Ionizing radiation

• d) Filtration systems only

Answer: a

Factors Influencing Sterilization

89. The presence of organic matter affects sterilization by:

• a) Enhancing the penetration of sterilizing agents

• b) Inactivating certain sterilizing agents

• c) Accelerating microbial destruction

• d) Reducing the temperature required for sterilization

Answer: b

90. Microbial resistance to sterilization depends on:

• a) Type of microorganism

• b) Environmental conditions (e.g., temperature, pH)

• c) Presence of protective structures like spores or biofilms

• d) All of the above

Answer: d

Sterilization Techniques

91. Ethylene oxide gas sterilization works by:

• a) Denaturing proteins and nucleic acids

• b) Generating free radicals

• c) Coagulating microbial enzymes

• d) Inducing DNA mutations

Answer: a

92. Ultrasonic waves are most commonly used to:

• a) Sterilize vaccines

• b) Clean surgical instruments

• c) Disinfect hospital air

• d) Destroy bacterial spores

Answer: b

93. A major disadvantage of using ethylene oxide gas is:

• a) Its inability to sterilize plastic materials

• b) Its toxicity and potential carcinogenicity

• c) Limited penetration of sterilizing gas

• d) High energy consumption

Answer: b

94. Flash sterilization is used for:

• a) Sterilizing large volumes of liquids

• b) Quickly sterilizing surgical instruments in emergencies

• c) Sterilizing heat-sensitive plastics

• d) Air sterilization in operating rooms

Answer: b

Miscellaneous

95. Sterilization of canned foods to destroy Clostridium botulinum spores is an example of:

• a) Autoclaving

• b) Commercial sterilization

• c) Pasteurization

• d) Radiation sterilization

Answer: b

96. The use of high-pressure steam for sterilization is based on the principle of:

• a) Protein denaturation at high temperatures

• b) Dehydration of microorganisms

• c) Disruption of bacterial DNA synthesis

• d) Formation of free radicals

Answer: a

97. Surface sterilization in healthcare often involves:

• a) Filtration

• b) Chemical disinfectants and UV light

• c) Gamma radiation

• d) Autoclaving

Answer: b

98. The advantage of sterilization by filtration is:

• a) Its rapid process time

• b) Suitability for heat-sensitive liquids

• c) High energy efficiency

• d) Ability to destroy bacterial spores

Answer: b

99. Heat-sensitive drugs are best sterilized by:

• a) Filtration

• b) Autoclaving

• c) UV light

• d) Gamma radiation

Answer: a

100. The primary use of steam sterilization in healthcare is to:

- a) Kill non-spore-forming pathogens

- b) Destroy all microbes, including spores

- c) Disinfect surfaces

- d) Remove organic debris

Answer: b