Q: Which equation best represents the formation of a chromophore in methylene blue chloride?

$$\text{Methylene blue chloride} \rightarrow \text{Methylene blue}^+ + \text{Chloride}^-$$

Question 1

Why is it important to allow a bacterial smear to air-dry completely before heat-fixing during slide preparation?

Accepted Answer

To prevent cell distortion and ensure proper adhesion to the slide.

Question 2

Which of the following best describes the role of the mordant in Gram staining?

Accepted Answer

It combines with the primary stain to form an insoluble complex in the cell wall.

Question 3

A student prepares a smear from a solid medium. Which step should they perform first?

Accepted Answer

Place 1 or 2 loopfuls of water on the slide.

Question 4

Which of the following stains is considered a basic stain and is attracted to the negatively charged bacterial cell wall?

Accepted Answer

Crystal violet

Question 5

In negative staining, why do bacteria appear clear or bright against a dark background?

Accepted Answer

The negatively charged chromophore is repelled by the bacterial cell surface.

Question 6

Which of the following is NOT a reason for fixing a bacterial smear?

Accepted Answer

To increase the rate of bacterial growth.

Question 7

During Gram staining, what is the effect of the decolorizing agent (ethanol) on Gram-negative bacteria?

Accepted Answer

It dissolves the outer lipopolysaccharide layer and washes out the CV-I complex.

Question 8

Which equation best represents the formation of a chromophore in methylene blue chloride?

Accepted Answer

$$	ext{Methylene blue chloride} ightarrow 	ext{Methylene blue}^+ + 	ext{Chloride}^-$$

Question 9

Which of the following is a key difference between Gram-positive and Gram-negative bacterial cell walls?

Accepted Answer

Gram-positive bacteria have multiple layers of peptidoglycan, while Gram-negative bacteria have a thin peptidoglycan layer surrounded by an outer membrane.

Question 10

Which of the following best explains why Gram-negative bacteria are generally more resistant to antibiotics?

Accepted Answer

Their outer membrane acts as a barrier to many antibiotics.

Question 11

Which of the following is a correct procedure for negative staining?

Accepted Answer

Do not heat-fix the smear; let it air-dry.

Question 12

Which of the following medical terms refers to abnormally fast breathing?

Accepted Answer

Tachypnea

Question 13

Which of the following is a plausible reason for using structural staining in microbiology?

Accepted Answer

To identify specific parts of microorganisms, such as flagella or endospores.

Question 14

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

Accepted Answer

Crystal violet, iodine, ethanol, safranin

Question 15

Which of the following is true about the use of methanol for fixing bacterial smears?

Accepted Answer

Methanol chemically fixes the smear by denaturing proteins.

Question 16

Which of the following best describes the appearance of Escherichia coli colonies on solid media?

Accepted Answer

Cream-colored colonies

Question 17

Which of the following is a plausible reason for using negative staining for coccobacilli?

Accepted Answer

Coccobacilli are short, oval bacilli that are difficult to stain with direct methods.

Question 18

Which of the following is a correct statement about the chromophore in acidic stains?

Accepted Answer

The chromophore is negatively charged and repelled by the bacterial cell surface.

Question 19

Which of the following best explains why heat-fixing is not used in negative staining?

Accepted Answer

Heat-fixing can distort cell morphology and is unnecessary since the stain does not penetrate the cells.

Preparation and Staining of Bacterial Smears: Techniques and Applications

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