Question 1

Which of the following best explains why agar is preferred over gelatin as a solidifying agent in microbiological culture media?

Accepted Answer

Agar remains solid at incubation temperatures because it melts at $$100^\circC $$and solidifies at about $$45^\circC.$$

Question 2

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

Accepted Answer

$$10 	imes 40 = 400$$

Question 3

Which of the following best describes the purpose of the streak plate technique in microbiology?

Accepted Answer

To isolate individual colonies from a mixed culture by creating a dilution gradient.

Question 4

During the Gram staining procedure, what is the primary reason that Gram-negative bacteria lose the crystal violet stain after the decolorization step?

Accepted Answer

Their outer membrane is dissolved by alcohol, allowing the stain to escape.

Question 5

Which of the following is NOT a correct step in the proper handwashing procedure in a microbiology lab?

Accepted Answer

Dry hands on your lab coat to avoid contamination.

Question 6

A microbiology student is preparing a bacterial smear from a solid culture. Which of the following is a critical difference compared to preparing a smear from a liquid culture?

Accepted Answer

Solid cultures require the addition of a drop of water to the slide before spreading the bacteria.

Question 7

Why are endospores difficult to stain using ordinary staining methods?

Accepted Answer

Endospores possess a tough keratin-like protein coat that resists penetration by dyes.

Question 8

In the genetic transformation experiment using GFP, which plate would you expect to show green fluorescent colonies, and why?

Accepted Answer

LB/amp/ara plate with +pGLO cells, because arabinose induces GFP expression in transformed cells.

Question 9

Which of the following best defines 'parfocal' as it relates to microscopy?

Accepted Answer

The ability of a microscope to maintain focus when switching between objectives.

Question 10

A student is performing a negative stain using nigrosin. What is the main advantage of this technique?

Accepted Answer

It allows observation of cell morphology without heat-fixing, preserving true size and shape.

Question 11

Which of the following best describes the function of a mordant in the Gram staining procedure?

Accepted Answer

It fixes the primary stain within the cell wall, enhancing retention of crystal violet.

Question 12

Why is it important to incubate agar plates in the inverted position?

Accepted Answer

To prevent condensation from dripping onto the agar surface and spreading colonies.

Question 13

Which of the following is a defining characteristic of fungi that distinguishes them from bacteria?

Accepted Answer

Fungi have chitin in their cell walls and are eukaryotic.

Question 14

A student calculates transformation efficiency using the following formula: $$	ext{Transformation Efficiency} = \frac{	ext{Number of colonies}}{	ext{Amount of DNA (\mu g)}}. If 100 $$colonies are obtained using 0.01 $$\mug of $$DNA, what is the transformation efficiency?

Accepted Answer

$$100 \div 0.01 = 10,000$$ colonies/$$\mug$$

Question 15

Which of the following best explains why heat fixing a bacterial smear is necessary before staining, and what is a potential problem if overheated?

Accepted Answer

Heat fixing kills bacteria and adheres them to the slide, but overheating can distort cell morphology.

Question 16

Which of the following statements about biosafety levels (BSLs) is correct?

Accepted Answer

BSL-2 requires lab coats, gloves, and sometimes face protection when working with moderate-risk agents.

Question 17

Which of the following best describes a 'pure culture' in microbiology?

Accepted Answer

A culture containing only one species of microorganism.

Question 18

A capsule stain is performed on a bacterial sample. Which of the following best explains why ordinary staining methods cannot be used to visualize capsules?

Accepted Answer

Capsules are non-ionic and do not bind to most stains, so a combination of negative and direct staining is required.

Question 19

Which of the following best describes the role of arabinose in the GFP genetic transformation experiment?

Accepted Answer

Arabinose induces the expression of the GFP gene in transformed cells.

Question 20

Which of the following is the correct order of steps in the Gram staining procedure?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Microbiology Lab Exam 1: Comprehensive Study Notes

Guida di studio - Domande di pratica

Study guide - Flashcard