Question 1

Which of the following best describes the lag phase in a closed pure batch system of bacterial growth?

Accepted Answer

Cells are adapting to new environmental conditions and synthesizing necessary enzymes.

Question 2

A bacterium that thrives at pH 2 and is isolated from acidic hot springs is best classified as which of the following?

Accepted Answer

Acidophile

Question 3

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

Accepted Answer

Catalase; $$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 4

Which of the following best distinguishes a facultative anaerobe from an obligate anaerobe?

Accepted Answer

Facultative anaerobes can use oxygen for metabolism but can also grow without it, while obligate anaerobes are harmed by oxygen.

Question 5

Which of the following is an example of a selective medium, and what is its purpose?

Accepted Answer

MacConkey agar; inhibits Gram-positive bacteria to select for Gram-negative bacteria.

Question 6

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

Accepted Answer

Plate count method, because it only counts living cells capable of forming colonies.

Question 7

Which of the following best describes the difference between sterilization and disinfection?

Accepted Answer

Sterilization destroys all forms of microbial life, including spores, while disinfection eliminates most pathogens but not necessarily spores.

Question 8

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; $$121^\circ C at 15 $$psi for 15 minutes.

Question 9

Which of the following chemical agents is most effective for sterilizing heat-sensitive medical equipment?

Accepted Answer

Ethylene oxide gas

Question 10

A microbiologist is tasked with decontaminating a laboratory bench after a spill of a bacterial culture. Which method is most appropriate and why?

Accepted Answer

Disinfection with a chemical agent, because it reduces the number of pathogens to safe levels on inanimate surfaces.

Question 11

Which of the following is a key factor to consider when choosing a germicide for hospital use, and why is it significant?

Accepted Answer

Presence of organic matter, because it can inactivate many germicides and reduce their effectiveness.

Question 12

Which of the following best describes the difference between phototrophs and heterotrophs?

Accepted Answer

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

Question 13

A culture medium contains high salt concentration and only allows halophilic bacteria to grow. This medium is best described as:

Accepted Answer

Selective medium

Question 14

Which of the following is a correct example of a psychrophile and its typical environment?

Accepted Answer

Bacteria isolated from Arctic sea ice, growing optimally at $$4^\circ C$$

Question 15

Which of the following statements about microaerophiles is correct?

Accepted Answer

They require oxygen at lower concentrations than is present in the atmosphere.

Question 16

A patient with a wound infection is treated with hydrogen peroxide. Which enzyme produced by some bacteria can neutralize this treatment, and what is the reaction?

Accepted Answer

Catalase; $$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 17

Which of the following best describes the stationary phase in a bacterial growth curve?

Accepted Answer

The rate of cell division equals the rate of cell death.

Question 18

Which of the following is a physical method used for sterilization, and for what is it most commonly used?

Accepted Answer

Filtration; sterilizing heat-sensitive solutions such as antibiotics.

Question 19

Which of the following best explains why thermophiles can survive at high temperatures?

Accepted Answer

They have heat-stable enzymes and membrane lipids that maintain function at elevated temperatures.

Question 20

A laboratory is testing a new disinfectant. Which factor should be controlled to ensure accurate results, and why?

Accepted Answer

Concentration of the disinfectant, because higher concentrations generally increase effectiveness.

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

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