Question 1

Which of the following best describes the growth pattern of an obligate anaerobe in thioglycolate broth?

Accepted Answer

Growth only at the bottom of the tube, where oxygen concentration is lowest.

Question 2

A student accidentally shakes a tube of thioglycolate broth before inoculation. What is the most likely consequence for interpreting oxygen requirements of bacteria?

Accepted Answer

The oxygen gradient will be disrupted, making it difficult to distinguish between oxygen requirements based on growth patterns.

Question 3

Which of the following is the correct chemical equation for the catalase reaction?

Accepted Answer

$$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 4

A culture of Pseudomonas aeruginosa is inoculated onto both an aerobic and an anaerobic nutrient agar plate. After incubation, growth is observed only on the aerobic plate. What is the most likely oxygen requirement classification for this organism?

Accepted Answer

Obligate aerobe

Question 5

Why are obligate anaerobes unable to survive in the presence of oxygen?

Accepted Answer

They lack catalase and superoxide dismutase, making them unable to detoxify reactive oxygen species.

Question 6

In an anaerobic jar, a Gas Pak is used to remove oxygen. Which chemical is primarily responsible for converting oxygen to water in this system?

Accepted Answer

Ascorbic acid

Question 7

A thioglycolate broth tube shows bacterial growth throughout the tube, but is densest at the top. Which oxygen requirement category does this most likely represent?

Accepted Answer

Facultative anaerobe

Question 8

During a catalase test, bubbles are observed after adding hydrogen peroxide to a bacterial colony. What does this indicate about the bacterium?

Accepted Answer

The bacterium produces catalase and can detoxify hydrogen peroxide.

Question 9

Which of the following statements about resazurin in thioglycolate broth is correct?

Accepted Answer

It acts as an indicator, turning pink in the presence of oxygen.

Question 10

A student observes that the resazurin strip in an anaerobic jar is pink after incubation. What does this indicate and how might it affect the experiment?

Accepted Answer

Oxygen is present in the jar, which may prevent obligate anaerobes from growing.

Question 11

Which of the following bacterial groups would you expect to have catalase enzyme activity?

Accepted Answer

Obligate aerobes and facultative anaerobes

Question 12

A microbe grows only in the middle of a thioglycolate broth tube, away from both the top and bottom. What is the most likely oxygen requirement classification?

Accepted Answer

Microaerophile

Question 13

Which of the following best explains why facultative anaerobes grow better in the presence of oxygen?

Accepted Answer

Aerobic respiration yields more ATP than anaerobic respiration or fermentation.

Question 14

In a candle jar, which of the following organisms would be LEAST likely to grow?

Accepted Answer

Obligate anaerobes

Question 15

Which of the following is a real-life application of the catalase test in clinical microbiology?

Accepted Answer

Distinguishing between Staphylococcus (catalase positive) and Streptococcus (catalase negative) species.

Question 16

Which of the following statements about sodium thioglycolate in thioglycolate broth is correct?

Accepted Answer

It reduces oxygen to water, creating an anaerobic environment.

Question 17

A patient sample is inoculated into thioglycolate broth. After incubation, growth is observed only at the top of the tube. Which of the following is the most likely identity of the organism?

Accepted Answer

Obligate aerobe

Question 18

Which of the following best describes the function of the Gas Pak in an anaerobic jar?

Accepted Answer

It chemically removes oxygen by converting it to water.

Question 19

A laboratory technician performs a catalase test on three unknown bacteria. The results are as follows: Bacterium A (bubbles), Bacterium B (no bubbles), Bacterium C (bubbles). Which of the following is the most likely oxygen requirement for Bacterium B?

Accepted Answer

Obligate anaerobe

Question 20

Which of the following best explains why microaerophiles cannot grow at the top of a thioglycolate broth tube?

Accepted Answer

Oxygen concentration at the top is too high and toxic for microaerophiles.

Microbiology Lab: Oxygen Requirements – Step-by-Step Study Guidance

Study Guide - Practice Questions

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