Question 1

Which of the following best explains why basic stains such as crystal violet are effective for simple staining of bacterial cells?

Accepted Answer

Basic stains are positively charged and ionically bond with the negatively charged bacterial cell surface.

Question 2

What is the primary purpose of using a simple stain in microbiology?

Accepted Answer

To increase the contrast of the cell, allowing observation of morphology, arrangement, and size.

Question 3

Which of the following is NOT a basic stain commonly used in simple staining procedures?

Accepted Answer

Eosin

Question 4

During the preparation of a bacterial smear from a solid medium, which step is essential to prevent cell distortion?

Accepted Answer

Allowing the smear to air dry completely before heat fixing

Question 5

Why is it important to rinse the slide with water after staining and before blotting dry?

Accepted Answer

To remove excess stain and prevent crystal formation

Question 6

A student observes that their stained bacterial cells appear blurry under the microscope. Which step was most likely performed incorrectly?

Accepted Answer

The slide was not blotted dry before adding oil and observing under oil immersion.

Question 7

Which of the following best describes the arrangement and morphology of Bacillus subtilis as seen after simple staining?

Accepted Answer

Rods in chains

Question 8

If a student accidentally skips the heat-fixing step, what is the most likely outcome when observing the slide?

Accepted Answer

The cells will wash off the slide during rinsing.

Question 9

Which of the following equations best represents the ionic interaction between a basic stain and a bacterial cell?

Accepted Answer

$$\mathrm{Stain}^+ + \mathrm{Cell}^- \rightarrow \mathrm{Stain{-}Cell}$$

Question 10

Which of the following is the correct sequence for preparing a bacterial smear from a solid medium?

Accepted Answer

Spread culture, air dry, heat fix, add stain

Question 11

A microbiologist wants to observe the arrangement of Micrococcus luteus. Which staining method and dye should be used for best results?

Accepted Answer

Simple stain with safranin

Question 12

Which of the following best explains why oil immersion is used when observing stained bacterial slides under a microscope?

Accepted Answer

Oil immersion increases the refractive index, reducing light loss and improving resolution.

Question 13

If a student observes both purple and pink cells on a slide stained with crystal violet, what is the most likely explanation?

Accepted Answer

The slide was contaminated with two different species.

Question 14

Which of the following is a critical safety step when disposing of used glass slides after staining?

Accepted Answer

Place slides in the sharps container on the bench.

Question 15

Which of the following best describes the role of the chromophore in a basic stain?

Accepted Answer

It is the colored portion of the stain that binds to the cell, allowing visualization.

Question 16

A student prepares a smear that is too thick. What is the most likely consequence when observing the slide?

Accepted Answer

Individual cells will be difficult to distinguish.

Question 17

Which of the following best explains why water is added first when preparing a smear from solid media?

Accepted Answer

To help evenly spread the bacteria into a thin film.

Question 18

Which of the following is the correct order of steps for a simple staining procedure?

Accepted Answer

Prepare smear, heat fix, apply stain, rinse, blot dry, observe under oil immersion

Question 19

Which of the following best describes the appearance of Staphylococcus epidermidis after simple staining?

Accepted Answer

Spherical cells in clusters

Question 20

A student accidentally uses acidic stain instead of a basic stain for simple staining. What is the most likely result?

Accepted Answer

The bacterial cells will appear colorless against a colored background.

Simple Staining in Microbiology: Principles, Methods, and Applications

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