Q: Which equation best represents the relationship between the thickness of peptidoglycan ($$t_{pg}) $$and the retention of crystal violet dye ($$R_{cv}) in $$Gram staining?

$$R_{cv} = k \times t_{pg}$$, where $$k is a $$constant

Question 1

Which of the following best explains why basic dyes are used in simple staining of bacteria?

Accepted Answer

Basic dyes carry a positive charge and are attracted to the negatively charged bacterial cell.

Question 2

A microbiologist observes oval, teal green structures within pink cells after staining a sample. Which staining technique and bacterial genera are most likely involved?

Accepted Answer

Endospore staining; Bacillus or Clostridium

Question 3

During Gram staining, what is the role of Gram’s iodine?

Accepted Answer

It serves as a mordant, binding to crystal violet and making it less soluble.

Question 4

Which equation best represents the relationship between the thickness of peptidoglycan ($$t_{pg}) $$and the retention of crystal violet dye ($$R_{cv}) in $$Gram staining?

Accepted Answer

$$R_{cv} = k 	imes t_{pg}$$, where $$k is a $$constant

Question 5

Why is heat required during the application of the primary stain in both acid-fast and endospore staining techniques?

Accepted Answer

Heat facilitates penetration of the dye through resistant cell walls or coats.

Question 6

A student performs a negative stain using nigrosin dye. What is the expected appearance of the bacteria under the microscope?

Accepted Answer

Bacteria appear colorless against a dark background.

Question 7

Which of the following best describes the purpose of aseptic transfer in microbiology?

Accepted Answer

To transfer an inoculum without contaminating the original culture, new medium, or environment.

Question 8

A sample is stained with carbolfuchsin, heated, and then decolorized with acid-alcohol. The cells appear fuchsia under the microscope. What does this indicate about the cell wall?

Accepted Answer

The cell wall contains mycolic acid, making the bacteria acid-fast.

Question 9

Which staining technique would be most appropriate for visualizing bacterial capsules, and why is heat-fixation avoided?

Accepted Answer

Capsule staining; heat-fixation is avoided because capsules can be damaged or degraded by heat.

Question 10

Which of the following equations best describes the probability ($$P_{cont}) of $$contamination during aseptic transfer as a function of the number of transfer steps ($$n) $$and the contamination rate per step ($$r$$)?

Accepted Answer

$$P_{cont} = 1 - (1 - r)^n$$

Question 11

A microbiologist needs to distinguish between bacteria based on their cell wall lipid content. Which staining technique should be used, and what is the primary dye?

Accepted Answer

Acid-fast staining; carbolfuchsin dye

Question 12

Which of the following statements about negative staining is correct?

Accepted Answer

Negative staining uses acidic dyes that color the background, leaving bacteria colorless.

Question 13

In capsule staining, what is the function of Congo red and acid fuchsin?

Accepted Answer

Congo red acts as a pH indicator for the background, acid fuchsin colors the bacteria.

Question 14

Which of the following best explains why endospore staining requires heating during the application of malachite green?

Accepted Answer

Heating increases the permeability of the endospore coat, allowing malachite green to penetrate.

Question 15

A sample is stained with crystal violet, Gram’s iodine, acetone-alcohol, and safranin. The cells appear pink under the microscope. What does this indicate?

Accepted Answer

The bacteria are Gram-negative with a thin peptidoglycan layer.

Question 16

Which staining technique would be most appropriate for observing bacteria that are easily distorted by heat-fixation?

Accepted Answer

Negative staining

Question 17

Which of the following is a structural staining technique used to observe features such as capsules and endospores?

Accepted Answer

Capsule staining

Question 18

A microbiologist wants to determine both the predominance of one type of bacteria over another and their cell size, shape, and arrangement in a sample. Which staining technique should be used?

Accepted Answer

Gram staining

Question 19

Which of the following best describes the outcome of acid-fast staining for bacteria lacking mycolic acid in their cell wall?

Accepted Answer

They lose the primary stain and take up methylene blue, appearing blue.

Microscopy and Staining Techniques in Microbiology

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