Question 1

Which of the following best describes the process of binary fission in bacteria?

Accepted Answer

A single cell elongates, replicates its DNA, forms a cross-wall, and separates into two identical cells.

Question 2

A bacterial culture starts with 10 cells. If the generation time is 20 minutes, how many cells will there be after 2 hours, assuming exponential growth? Use the formula $$N_f = (N_i)2^n.$$

Accepted Answer

$$N_f = 10 	imes 2^6$ = 640$$

Question 3

Which phase of the bacterial growth curve is characterized by a balance between cell division and cell death?

Accepted Answer

Stationary phase

Question 4

A microbiologist wants to count the number of viable bacteria in a water sample. Which method should they use?

Accepted Answer

Plate count method after serial dilution

Question 5

Which of the following best explains why food with high sugar or salt content is less likely to spoil?

Accepted Answer

High osmotic pressure causes plasmolysis in bacteria, inhibiting their growth.

Question 6

Which type of microorganism would most likely be responsible for food spoilage in a refrigerator?

Accepted Answer

Psychrotrophs

Question 7

A bacterium that can grow in the presence or absence of oxygen, but grows better with oxygen, is classified as:

Accepted Answer

Facultative anaerobe

Question 8

Which enzyme is responsible for converting superoxide radicals to hydrogen peroxide and oxygen in bacteria?

Accepted Answer

Superoxide dismutase (SOD)

Question 9

A bacterium that requires many organic growth factors and cannot grow on minimal media is described as:

Accepted Answer

Fastidious

Question 10

Which of the following best describes the function of a candle jar in microbiology labs?

Accepted Answer

It increases carbon dioxide levels and reduces oxygen, suitable for microaerophiles.

Question 11

Which of the following is a trace element required by bacteria for enzyme function?

Accepted Answer

Iron

Question 12

A bacterium is placed in a solution with a higher concentration of NaCl than inside the cell. What will most likely happen?

Accepted Answer

The cell will undergo plasmolysis as water leaves the cell.

Question 13

Which of the following best describes a neutrophile?

Accepted Answer

A bacterium that grows best at pH 7

Question 14

Which of the following equations correctly represents the catalase reaction?

Accepted Answer

$$2 H_2O_2 \rightarrow 2 H_2O + O_2$

Question 15

Which of the following best explains why Bacillus cereus can multiply in improperly cooled rice?

Accepted Answer

The temperature remains in the danger zone (20-50°C) for several hours, allowing rapid bacterial growth.

Question 16

Which of the following statements about mesophiles is correct?

Accepted Answer

They grow best at temperatures between 25°C and 40°C.

Question 17

A microbiologist uses a spectrophotometer to estimate bacterial growth. What is being measured?

Accepted Answer

The turbidity (cloudiness) of the culture, which correlates with cell density

Question 18

Which of the following best describes an obligate anaerobe?

Accepted Answer

It cannot grow in the presence of oxygen.

Question 19

Which of the following is a correct statement about nitrogen requirements for bacteria?

Accepted Answer

Some bacteria can fix atmospheric nitrogen ($$N_2) $$into usable forms.

Question 20

Which of the following best describes a chemotroph?

Accepted Answer

An organism that gains energy from chemical compounds.

Microbial Growth: Nutrition, Environmental Factors, and Measurement

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