Question 1

Which group of microorganisms is most likely to be responsible for food spoilage in a refrigerator set at 4°C?

Accepted Answer

Psychrotrophs

Question 2

Why are phosphate salts commonly added to microbiological culture media?

Accepted Answer

They maintain a stable pH by acting as buffers and also provide phosphorus needed for cellular components.

Question 3

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

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 4

Which of the following best describes the role of superoxide dismutase (SOD) in aerobic bacteria?

Accepted Answer

It neutralizes superoxide radicals by converting them to hydrogen peroxide and oxygen.

Question 5

A patient develops an infection on a catheter that is difficult to treat with antibiotics. Which microbial property is most likely responsible?

Accepted Answer

The bacteria form biofilms that are highly resistant to microbicides.

Question 6

Which phase of the bacterial growth curve is characterized by rapid cell division and is when bacteria are most susceptible to antibiotics targeting cell wall synthesis?

Accepted Answer

Log (exponential) phase

Question 7

A microbiologist wants to isolate a pure culture from a mixed bacterial sample. Which method should they use?

Accepted Answer

Streak plate method

Question 8

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

Accepted Answer

They lack enzymes to neutralize toxic forms of oxygen.

Question 9

A bacterial culture is growing in a medium with limited nutrients. After a period of rapid growth, the number of viable cells remains constant. Which phase is this?

Accepted Answer

Stationary phase

Question 10

Which of the following equations correctly represents the total number of cells after $$n$$ generations, starting from a single cell?

Accepted Answer

$$2^n$$

Question 11

A sample of water is filtered and the filter is placed on a selective agar. After incubation, 214 colonies are counted. What is the bacterial concentration in the original 100 mL sample?

Accepted Answer

214 bacteria per 100 mL

Question 12

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

Accepted Answer

Turbidity measurement

Question 13

Which chemical element is primarily used in the synthesis of nucleic acids and ATP in microbial cells?

Accepted Answer

Phosphorus

Question 14

A bacterium is classified as a facultative anaerobe. Which of the following best describes its growth in a test tube of solid medium?

Accepted Answer

Growth throughout the tube, but denser at the top

Question 15

Which of the following best explains why biofilms are a major concern in medical settings?

Accepted Answer

Biofilms are 1000x more resistant to microbicides and are involved in 70% of infections.

Question 16

Which of the following best describes the function of buffers in bacterial culture media?

Accepted Answer

They maintain a stable pH to support optimal microbial growth.

Question 17

A researcher measures the cloudiness of a bacterial culture using a spectrophotometer. Which method of growth estimation is being used?

Accepted Answer

Turbidity measurement

Question 18

Which of the following is a correct description of the lag phase in the bacterial growth curve?

Accepted Answer

Intense metabolic activity with little or no increase in cell number

Question 19

Which of the following best explains why food with a high salt concentration is less likely to spoil?

Accepted Answer

High salt concentration causes plasmolysis in most bacteria, inhibiting their growth.

Question 20

Which of the following is a multi-step process that bacteria use to form biofilms on surfaces?

Accepted Answer

Bacteria settle, communicate via quorum sensing, secrete inducers, and form a protective matrix.

Microbial Growth: Requirements, Classification, and Measurement

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