Question 1

Which of the following best describes the main difference between chemically defined and complex media used for microbial growth?

Accepted Answer

Chemically defined media have a known exact chemical composition, while complex media contain extracts and digests of natural products with variable composition.

Question 2

A microbiologist wants to culture an obligate anaerobe. Which of the following methods would be most appropriate to ensure the survival and growth of this organism?

Accepted Answer

Use a reducing medium containing thioglycolate and store in a tightly capped tube.

Question 3

Which of the following best explains why food preservation techniques such as salting or sugaring are effective?

Accepted Answer

They create a hypertonic environment, causing plasmolysis in most bacteria.

Question 4

A bacterial culture is exposed to radioactive sulfur ($$^{35}S). In $$which of the following molecules would you expect to find the radioactive label?

Accepted Answer

Proteins containing methionine or cysteine

Question 5

Which of the following equations correctly represents the action of superoxide dismutase?

Accepted Answer

$$ \mathrm{O_2^- + 2H^+ \xrightarrow{superoxide\ dismutase} H_2O_2 + O_2} $$

Question 6

Which group of bacteria would be most likely to survive and grow in a jar with a burning candle (candle jar)?

Accepted Answer

Capnophiles

Question 7

A patient develops a chronic infection associated with a catheter. Which microbial property most likely contributes to the persistence of this infection?

Accepted Answer

Biofilm formation

Question 8

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

Accepted Answer

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

Question 9

Which of the following is a direct method for measuring bacterial cell growth?

Accepted Answer

Counting colonies on a plate after serial dilution

Question 10

A microbiologist streaks a mixed bacterial sample onto a selective medium. What is the most likely outcome?

Accepted Answer

Only bacteria with specific traits will grow, suppressing unwanted microbes.

Question 11

Which of the following best explains why obligate anaerobes are killed by oxygen?

Accepted Answer

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

Question 12

Which of the following best describes the function of biofilms in bacterial survival?

Accepted Answer

Biofilms shelter bacteria from harmful factors such as antibiotics and the host immune system.

Question 13

Which of the following statements about generation time is correct?

Accepted Answer

Generation time is the time required for a bacterial cell to divide and its population to double.

Question 14

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

Accepted Answer

They use oxygen as a final electron acceptor, producing more ATP through aerobic respiration.

Question 15

Which of the following is a correct use of differential media?

Accepted Answer

To distinguish between bacteria that ferment lactose and those that do not.

Question 16

A bacterium is placed in a hypertonic solution. What is the most likely outcome?

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 17

Which of the following best describes the role of phosphorus in microbial cells?

Accepted Answer

It is required for the synthesis of phospholipids, ATP, and nucleic acids.

Question 18

Which of the following best describes the streak-plate method?

Accepted Answer

It is used to isolate pure cultures from a mixed sample.

Question 19

Which of the following is a reason why only about 1% of all bacteria can be successfully cultured in the laboratory?

Accepted Answer

Most bacteria require complex interactions with other microbes or specific environmental conditions not replicated in the lab.

Microbial Growth: Physical and Chemical Requirements, Culturing, and Measurement

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