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 helps to evenly disperse the bacterial cells for 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 cells to wash off.

Question 6

Which of the following best describes the chemical interaction during simple staining with methylene blue?

Accepted Answer

The positively charged chromophore binds to the negatively charged cell surface.

Question 7

Which of the following is a correct sequence for preparing a bacterial smear from a liquid culture?

Accepted Answer

Add bacteria, spread, air dry, heat fix

Question 8

Why should you avoid rubbing or dragging bibulous paper over the stained smear when drying?

Accepted Answer

It may remove the sample from the slide.

Question 9

Which of the following dyes is an example of a basic dye used in simple staining?

Accepted Answer

Crystal violet

Question 10

What is the main reason for using oil immersion when observing stained bacterial smears?

Accepted Answer

To increase the resolving power and clarity of the image.

Question 11

Which of the following statements about acidic dyes is correct?

Accepted Answer

Acidic dyes have a negative charge and stain the background.

Question 12

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

Accepted Answer

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

Question 13

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

Accepted Answer

Applying a mordant

Question 14

Which of the following best describes the role of chromophores in staining?

Accepted Answer

Chromophores are ions that impart color to the dye.

Question 15

A student accidentally overheats a slide during heat fixation. What is a possible consequence?

Accepted Answer

The cells may become distorted and difficult to identify.

Question 16

Which of the following is a plausible reason for observing no stained cells after performing a simple stain, despite following the staining protocol correctly?

Accepted Answer

The smear was washed off during rinsing due to inadequate heat fixation.

Question 17

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.

Simple Stain and Smear Preparation in Microbiology

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