Question 1

Which of the following best describes a thermophile?

Accepted Answer

A microbe that grows best at temperatures between $$50^\circ C$$ and $$60^\circ C$$

Question 2

Why is the pH of culture media often controlled during microbial growth experiments?

Accepted Answer

To prevent the accumulation of acidic or basic metabolic byproducts that could inhibit microbial growth

Question 3

A patient receives a hypertonic saline solution intravenously. What is the most likely effect on bacteria present in the bloodstream?

Accepted Answer

Water will leave the bacterial cells, causing plasmolysis and inhibiting growth

Question 4

Which of the following is a primary use of phosphorus in microbial cells?

Accepted Answer

Formation of nucleic acids and ATP

Question 5

An obligate aerobe is characterized by which of the following oxygen requirements?

Accepted Answer

Requires oxygen for growth and cannot grow without it

Question 6

Which enzyme do aerobes use to neutralize hydrogen peroxide, a toxic form of oxygen?

Accepted Answer

Catalase, which converts $$2H_2O_2 \rightarrow 2H_2O + O_2$

Question 7

Biofilms are medically significant because:

Accepted Answer

They protect microbes from antibiotics and the immune system, leading to persistent infections

Question 8

Which of the following best distinguishes a chemically defined medium from a complex medium?

Accepted Answer

A chemically defined medium has a known exact chemical composition, while a complex medium contains ingredients of unknown composition

Question 9

Which type of medium would you use to isolate Salmonella from a stool sample, and why?

Accepted Answer

Selective medium, because it inhibits the growth of non-Salmonella bacteria

Question 10

Why are candle jars used in microbiology laboratories?

Accepted Answer

To create a low-oxygen, high-carbon dioxide environment for growing microaerophiles

Question 11

A laboratory is working with a microbe that poses a high risk of aerosol-transmitted infection and for which there is no available vaccine or treatment. Which biosafety level is required?

Accepted Answer

Biosafety Level 4 (BSL-4)

Question 12

What is a pure culture?

Accepted Answer

A culture containing only one species or strain of microorganism

Question 13

Which step is essential for isolating a pure culture using the streak plate method?

Accepted Answer

Sequentially diluting the inoculum across the surface of the agar to obtain isolated colonies

Question 14

Which preservation method involves removing water from a microbial culture under vacuum after freezing, allowing long-term storage?

Accepted Answer

Lyophilization (freeze-drying)

Question 15

Bacterial growth is defined as:

Accepted Answer

An increase in the number of cells via binary fission

Question 16

During which phase of the bacterial growth curve is the generation time shortest and cell division most rapid?

Accepted Answer

Log (exponential) phase

Question 17

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

Accepted Answer

Plate count method

Question 18

What is the main difference between direct and indirect methods of measuring cell growth?

Accepted Answer

Direct methods count individual cells, while indirect methods estimate cell numbers based on other parameters

Question 19

Which of the following is an example of an indirect method for measuring microbial growth?

Accepted Answer

Measuring turbidity using a spectrophotometer and applying the Beer-Lambert law: $$A = \varepsilon l c$$

Question 20

A researcher wants to determine 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

Microbial Growth: Environmental Factors, Media, and Measurement

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