Question 1

Which of the following best describes the function of the condenser on a compound light microscope?

Accepted Answer

It focuses light onto the specimen to improve image clarity.

Question 2

A student is using a 40x objective lens and a 10x ocular lens on a microscope. What is the total magnification being used?

Accepted Answer

$$40 	imes 10 = 400$$

Question 3

Which of the following is the primary reason for using aseptic technique when transferring bacterial cultures?

Accepted Answer

To prevent contamination of the culture and the environment.

Question 4

During a Gram stain, what is the purpose of the iodine step?

Accepted Answer

To act as a mordant and fix the crystal violet dye inside the cells.

Question 5

A microbiologist is preparing a PCR reaction. Which of the following is NOT a typical component added to the PCR master mix?

Accepted Answer

Restriction enzymes

Question 6

Which of the following best explains why Taq polymerase is used in PCR?

Accepted Answer

It is heat-stable and can withstand the high temperatures used during PCR cycles.

Question 7

A scientist is using the Kirby-Bauer disk diffusion method to test antibiotic susceptibility. What is measured to determine the effectiveness of an antibiotic?

Accepted Answer

The diameter of the zone of inhibition in millimeters

Question 8

Which of the following statements about CRISPR is correct?

Accepted Answer

CRISPR is a bacterial adaptive immune system that uses RNA-guided nucleases to target specific DNA sequences.

Question 9

In a bacterial identification experiment, the SIM (Sulfide-Indole-Motility) test is used. What does a black precipitate in the medium indicate?

Accepted Answer

The bacteria produce hydrogen sulfide ($$H_2S).$$

Question 10

A student is preparing DNA for PCR and adds EDTA to the extraction buffer. What is the main function of EDTA in this context?

Accepted Answer

To chelate divalent cations and inhibit DNase activity.

Question 11

Which of the following best describes the function of the 16S rRNA gene in bacterial identification?

Accepted Answer

It is highly conserved and used as a molecular marker for phylogenetic studies.

Question 12

During a catalase test, a microbiologist adds hydrogen peroxide to a bacterial colony. Bubbling is observed. What does this indicate?

Accepted Answer

The bacteria produce the enzyme catalase, which breaks down $$H_2O_2$$ into water and oxygen.

Question 13

A student is performing a streak plate technique. What is the primary goal of this method?

Accepted Answer

To isolate single colonies from a mixed culture.

Question 14

Which of the following best explains why a negative control is included in a PCR experiment?

Accepted Answer

To check for contamination by ensuring no amplification occurs in the absence of template DNA.

Question 15

A microbiologist is using the SIM test to identify bacteria. Which result would indicate positive motility?

Accepted Answer

Diffuse growth radiating from the stab line.

Question 16

Which of the following is a correct description of the function of the CRISPR-associated protein Cas9?

Accepted Answer

It is a nuclease that introduces double-stranded breaks at specific DNA sequences.

Question 17

A student is performing a TSI (Triple Sugar Iron) agar test. Which result indicates the production of hydrogen sulfide ($$H_2S$$)?

Accepted Answer

Black precipitate in the butt of the tube

Question 18

Which of the following best describes the purpose of using a positive control in a biochemical test?

Accepted Answer

To ensure the test reagents are functioning properly by producing a known positive result.

Question 19

In the context of bacterial oxygen requirements, which of the following best describes a facultative anaerobe?

Accepted Answer

It can grow with or without oxygen, but grows better in its presence.

Question 20

A scientist is using PCR to amplify a segment of DNA. If the initial number of DNA molecules is 2, how many DNA molecules will be present after 5 cycles, assuming 100% efficiency? Use the formula $$N = N_0$ 	imes 2^n$$, where $$N_0 is $$the initial number and $$n is $$the number of cycles.

Accepted Answer

$$N = 2 	imes 2^5$ = 64$$

Microbiology 271 Lab Study Guide: Techniques, Tools, and Applications

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