Question 1

Which of the following best explains why basic dyes are effective for staining bacterial cells?

Accepted Answer

Basic dyes are cationic and bind to the negatively charged cell surface.

Question 2

During smear preparation from a solid culture, why is it important to add a drop of water to the slide before mixing the colony?

Accepted Answer

Water allows the bacterial cells to be evenly spread into a thin smear.

Question 3

What is the primary purpose of heat fixation in smear preparation?

Accepted Answer

To adhere the cells to the slide and kill most of them.

Question 4

Which of the following is NOT a characteristic that can be determined using a simple stain?

Accepted Answer

Cell wall composition

Question 5

A student prepares a smear, stains it with methylene blue, and observes almost no cells under oil immersion. Which of the following is a likely reason for this result?

Accepted Answer

The student did not heat-fix the smear, causing the cells to wash off.

Question 6

Which of the following dyes can be used as a simple stain? Select all that apply.

Accepted Answer

Crystal violet

Question 7

What is the chemical property of the chromophore in basic dyes that allows them to stain bacterial cells?

Accepted Answer

The chromophore is positively charged.

Question 8

Which step in the simple staining procedure is most likely to cause loss of the sample if performed incorrectly?

Accepted Answer

Rinsing the slide too vigorously

Question 9

Why should bibulous paper be used to blot the slide instead of rubbing it after staining?

Accepted Answer

Rubbing the slide may remove the sample from the slide.

Question 10

Which of the following best describes the difference between simple and differential stains?

Accepted Answer

Simple stains reveal basic morphology, while differential stains distinguish cells based on specific characteristics.

Question 11

A student accidentally skips the air-drying step before heat-fixing a smear. What is the most likely outcome?

Accepted Answer

The cells may be distorted or destroyed due to boiling.

Question 12

Which of the following best explains why acidic dyes are used for negative staining?

Accepted Answer

Acidic dyes are anionic and are repelled by the negatively charged cell surface, staining the background.

Question 13

Which of the following is the correct formula for total magnification when using a compound light microscope?

Accepted Answer

$$	ext{Total Magnification} = 	ext{Objective Lens Magnification} 	imes 	ext{Ocular Lens Magnification}$$

Question 14

Which of the following is a possible effect of excessive heat during heat fixation?

Accepted Answer

It distorts the cell morphology.

Question 15

Which of the following best describes the arrangement of cocci in a chain?

Accepted Answer

Streptococci

Question 16

If a student observes both large, irregularly shaped cells and small, uniformly shaped cells in an oral smear, what is the most likely explanation?

Accepted Answer

The large cells are likely cheek cells, and the small cells are bacteria.

Question 17

Which of the following steps is NOT part of the simple staining procedure?

Accepted Answer

Applying a mordant

Question 18

Why is it important to use aseptic technique when preparing a smear from a bacterial culture?

Accepted Answer

To avoid contamination of the culture and the environment.

Question 19

Which of the following best describes the role of the chromophore in a staining solution?

Accepted Answer

It imparts color to the dye, allowing visualization of cells.

Question 20

A student uses Congo red to stain a bacterial smear. What will be the most likely observation under the microscope?

Accepted Answer

The background will be stained, and the bacterial cells will appear clear.

Simple Stain and Smear Preparation: Principles and Laboratory Techniques

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