Question 1

A microbiologist is studying a bacterium that grows optimally at 37°C and is commonly found in the human body. Based on the temperature growth curve, which group does this bacterium most likely belong to?

Accepted Answer

Mesophiles

Question 2

Which of the following best explains why obligate anaerobes are unable to survive in the presence of oxygen?

Accepted Answer

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

Question 3

A food sample is stored at 10°C. Which group of microorganisms is most likely to cause spoilage under these conditions?

Accepted Answer

Psychrotrophs

Question 4

A bacterial cell is placed in a solution containing 10% NaCl. What is the most likely outcome for a typical non-halophilic bacterium?

Accepted Answer

The cell will undergo plasmolysis due to water leaving the cell.

Question 5

Which of the following media would you use to isolate a bacterium that is unable to synthesize its own growth factors and requires many nutrients provided in the medium?

Accepted Answer

Chemically defined medium

Question 6

A microbiologist wants to count the number of viable bacteria in a water sample expected to have low bacterial numbers. Which method is most appropriate?

Accepted Answer

Filtration

Question 7

Which equation correctly describes the total number of cells after $$n$$ generations, starting from a single cell, during binary fission?

Accepted Answer

$$N = 2^n$$

Question 8

A culture medium contains yeast extract, peptone, and beef extract. Which type of medium is this?

Accepted Answer

Complex medium

Question 9

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death, resulting in no net increase in cell number?

Accepted Answer

Stationary phase

Question 10

A sample is diluted 1:1000 and 0.1 mL is plated. If 30 colonies are counted, what is the concentration of bacteria in the original sample (in CFU/mL)? Use the formula $$	ext{CFU/mL} = \frac{	ext{Number of colonies}}{	ext{Volume plated (mL)} 	imes 	ext{Dilution factor}}.$$

Accepted Answer

$$3 	imes 10^4$

Question 11

Which of the following best describes the purpose of selective media?

Accepted Answer

To suppress unwanted microbes and encourage desired microbes

Question 12

A microbiologist is using a spectrophotometer to estimate bacterial growth in a liquid culture. What is being measured?

Accepted Answer

Turbidity

Question 13

Which of the following statements about agar is FALSE?

Accepted Answer

Agar is a protein used as a nutrient source.

Question 14

Which type of microorganism would you expect to find growing in a hot spring at 90°C?

Accepted Answer

Hyperthermophile

Question 15

A bacterium is described as a facultative anaerobe. Which of the following best describes its growth in the presence and absence of oxygen?

Accepted Answer

It grows better in the presence of oxygen but can grow without it.

Question 16

Which of the following is a trace element required by microorganisms for enzymatic activity?

Accepted Answer

Iron

Question 17

A microbiologist wants to isolate a pure culture from a mixed sample. Which method should be used?

Accepted Answer

Streak plate method

Question 18

Which of the following best describes the lag phase of bacterial growth?

Accepted Answer

Cells are metabolically active but not dividing rapidly.

Question 19

Which of the following is NOT a direct method for measuring microbial growth?

Accepted Answer

Turbidity

Question 20

A yeast cell divides by forming a small outgrowth that eventually separates from the parent cell. This process is called:

Accepted Answer

Budding

Microbial Growth: Requirements, Culture, and Measurement

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