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 and grows best in acidic environments (low pH).

Question 3

A bacterium isolated from deep-sea hydrothermal vents grows optimally at 80°C and can survive in high pressure. Which term best describes this organism?

Accepted Answer

Thermophile

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 facultative anaerobe?

Accepted Answer

Escherichia coli

Question 7

Which statement correctly compares differential and selective media?

Accepted Answer

Differential media allow distinction between organisms based on biochemical reactions, while selective media inhibit the growth of certain organisms.

Question 8

Which of the following is an example of a selective medium?

Accepted Answer

MacConkey agar

Question 9

A microbiologist wants to count the number of viable bacteria in a sample. Which method should they use?

Accepted Answer

Serial dilution and plate count

Question 10

Which physical method is most appropriate for sterilizing heat-sensitive medical instruments?

Accepted Answer

Filtration using a $0.22 \mu m$ membrane filter

Question 11

Which chemical agent is classified as a high-level disinfectant and is commonly used for sterilizing surgical instruments?

Accepted Answer

Glutaraldehyde

Question 12

Which term refers to the process of reducing microbial numbers to safe levels, but not necessarily eliminating all microbes?

Accepted Answer

Sanitization

Question 13

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

Accepted Answer

Color of the germicide

Question 14

Which method is most effective for sterilizing laboratory media and solutions?

Accepted Answer

Autoclaving at $121^\circ C$ and 15 psi for 15 minutes

Question 15

Which physical method is best for decontaminating surfaces in a hospital room?

Accepted Answer

UV irradiation

Question 16

Which of the following statements about phototrophs and heterotrophs is correct?

Accepted Answer

Phototrophs use light as an energy source, while heterotrophs obtain energy from organic compounds.

Question 17

Which of the following is an example of a phototrophic microorganism?

Accepted Answer

Cyanobacteria

Question 18

Which process is used to destroy all forms of microbial life, including spores?

Accepted Answer

Sterilization

Question 19

A hospital uses ethylene oxide gas to sterilize heat-sensitive equipment. What is the main advantage of this method?

Accepted Answer

It can sterilize without damaging heat-sensitive materials.

Question 20

Which of the following best explains why the presence of organic matter can reduce the effectiveness of a germicide?

Accepted Answer

Organic matter can react with and neutralize the germicide, reducing its activity.

Microbial Growth, Environmental Adaptations, and Control Methods: Study Notes

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