Q: A microbiologist wants to sterilize a solution without heating it. Which method should be used?

Filtration through a $$0.22 \\mu m$$ membrane

Question 1

Which phase of bacterial growth in a closed batch system is characterized by active cell division and exponential increase in cell number, and how does this differ from growth in a chemostat system?

Accepted Answer

Log (exponential) phase; in a chemostat, cells can be maintained in log phase by continuous nutrient addition and waste removal.

Question 2

Which of the following best describes an acidophile?

Accepted Answer

A microorganism that prefers environments with low pH, such as pH 2.

Question 3

A bacterium isolated from deep-sea hydrothermal vents is found to grow optimally at 80°C and high pressure. Which terms best describe this organism?

Accepted Answer

Thermophile and barophile

Question 4

Obligate anaerobes are unable to survive in the presence of oxygen because:

Accepted Answer

They lack enzymes such as superoxide dismutase and catalase to detoxify reactive oxygen species.

Question 5

Which enzyme is commonly used by oxygen-tolerant organisms to eliminate superoxide radicals, and what is the reaction it catalyzes?

Accepted Answer

Superoxide dismutase; $$2O_2^- + 2H^+ \rightarrow H_2O_2 + O_2$

Question 6

Which of the following is an example of a photoautotroph?

Accepted Answer

Cyanobacteria

Question 7

Which statement correctly distinguishes between differential and selective media?

Accepted Answer

Differential media allow differentiation of organisms based on metabolic properties, while selective media inhibit the growth of certain organisms.

Question 8

Which method is considered a direct method for counting microbial cells?

Accepted Answer

Viable plate count

Question 9

Which term refers to the process of reducing the number of pathogenic microorganisms to a level that is safe for public health, but not necessarily eliminating all microbes?

Accepted Answer

Disinfection

Question 10

A hospital uses autoclaving to prepare surgical instruments. Which physical method is being employed, and what is the standard condition for this process?

Accepted Answer

Moist heat sterilization; $$121^\	ext{o}C at 15 $$psi for 15 minutes

Question 11

Which chemical agent is most appropriate for sterilizing heat-sensitive medical equipment?

Accepted Answer

Glutaraldehyde

Question 12

Which of the following is NOT a factor to consider when choosing an appropriate germicide?

Accepted Answer

Color of the germicide

Question 13

A microbiologist wants to sterilize a solution without heating it. Which method should be used?

Accepted Answer

Filtration through a $$0.22 \mu m$$ membrane

Question 14

Which physical method is most effective for decontaminating laboratory surfaces?

Accepted Answer

UV irradiation

Question 15

Which of the following best describes the mechanism of action of alcohol-based disinfectants?

Accepted Answer

Denaturation of proteins and disruption of cell membranes

Question 16

A patient develops an infection after surgery. The hospital uses both sterilization and disinfection protocols. Which process ensures the complete destruction of all forms of microbial life, including spores?

Accepted Answer

Sterilization

Question 17

Which of the following is a common misconception about facultative anaerobes?

Accepted Answer

They are unable to detoxify reactive oxygen species.

Question 18

Which of the following best explains why halophiles thrive in high-salt environments?

Accepted Answer

They accumulate compatible solutes to balance osmotic pressure.

Question 19

Which process is most appropriate for preparing a nutrient broth for culturing bacteria in a research laboratory?

Accepted Answer

Sterilization by autoclaving

Question 20

A food processing plant wants to reduce microbial contamination on equipment surfaces. Which method is most suitable for routine cleaning?

Accepted Answer

Disinfection with quaternary ammonium compounds

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