Question 1

Which of the following correctly identifies the primary and secondary stains used in Gram staining?

Accepted Answer

Primary: Crystal violet; Secondary: Safranin

Question 2

A microbiologist is testing an unknown bacterium using acid-fast staining. The primary stain is applied, followed by decolorization and a counterstain. If the bacterium retains the primary stain, what can be concluded about its cell wall?

Accepted Answer

It contains a high concentration of mycolic acids.

Question 3

Which of the following best describes a selective medium?

Accepted Answer

A medium that inhibits the growth of some organisms while allowing others to grow.

Question 4

MacConkey agar is used in a clinical lab to culture a stool sample. Colonies appear pink. Which of the following is true about MacConkey agar and the bacteria growing on it?

Accepted Answer

MacConkey agar is both selective and differential; pink colonies indicate lactose fermentation.

Question 5

A blood agar plate shows colonies surrounded by a clear, colorless zone. What type of hemolysis is this, and what does it indicate?

Accepted Answer

Beta hemolysis; complete lysis of red blood cells

Question 6

During an endospore stain, which color indicates the presence of endospores after the staining process is complete?

Accepted Answer

Green

Question 7

A student adds iodine to a starch agar plate after bacterial growth. The area around the colonies remains clear while the rest of the plate turns blue-black. What does this indicate about the bacteria?

Accepted Answer

The bacteria produce amylase and hydrolyze starch.

Question 8

In an OF-glucose test, a tube covered with mineral oil turns yellow while the uncovered tube remains green. What does this result indicate about the bacterium's metabolism?

Accepted Answer

The bacterium is fermentative.

Question 9

Which of the following best defines a competent cell in the context of bacterial transformation?

Accepted Answer

A cell capable of taking up foreign DNA from its environment.

Question 10

Ampicillin is used in a bacterial transformation experiment. What is the purpose of including ampicillin in the agar plate after transformation?

Accepted Answer

To select for bacteria that have successfully taken up the plasmid containing the ampicillin resistance gene.

Question 11

A student performs a transformation experiment but observes no colonies on the amp-agar plate. Which of the following is the most likely explanation?

Accepted Answer

The competent cells did not take up the plasmid with the ampicillin resistance gene.

Question 12

In the Ames test, what does the appearance of colonies around a chemical spot on the plate indicate?

Accepted Answer

The chemical is a potential mutagen.

Question 13

After exposing bacteria to UV radiation, no colonies grow on the plate. What is the most likely interpretation?

Accepted Answer

The UV radiation caused lethal mutations or cell death.

Question 14

Which of the following equations best represents the hydrolysis of starch by amylase?

Accepted Answer

$$	ext{(C}_6	ext{H}_{10}	ext{O}_5	ext{)}_n + n\ 	ext{H}_2	ext{O} \xrightarrow{	ext{amylase}} n\ 	ext{C}_6	ext{H}_{12}	ext{O}_6$$

Question 15

Which of the following best explains why competent cells alone will not grow on an amp-agar plate?

Accepted Answer

They lack the plasmid encoding ampicillin resistance.

Question 16

A sample is stained using the endospore stain. Under the microscope, you observe both green and red structures. What does this indicate about the sample?

Accepted Answer

The sample contains both endospores (green) and vegetative cells (red).

Question 17

Which of the following media is both selective and differential?

Accepted Answer

MacConkey agar

Question 18

A bacterium is inoculated into OF-glucose media. Both the aerobic and anaerobic tubes turn yellow. What does this result indicate?

Accepted Answer

The bacterium can metabolize glucose both oxidatively and fermentatively.

Question 19

Which of the following best describes the purpose of the UV radiation mutation test in the Ames test?

Accepted Answer

To determine if UV radiation can induce mutations in bacteria.

Question 20

Which of the following is the correct sequence of steps for Gram staining?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Microbiology Lab Study Guide: Staining, Media, Metabolism, Transformation, and Mutation

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