Question 1

Which of the following best explains why basic (cationic) stains are commonly used to stain bacterial cells?

Accepted Answer

Bacterial cells have a net negative charge, which attracts the positively charged chromophore of basic stains.

Question 2

During the preparation of a bacterial smear from a solid medium, why is it important to use only a small amount of bacterial growth?

Accepted Answer

Using too much bacteria can result in a smear that is too thick, making it difficult to observe individual cells under the microscope.

Question 3

What is the primary purpose of heat-fixing a bacterial smear before staining?

Accepted Answer

To kill the bacteria and adhere them to the slide surface.

Question 4

If a sodium atom loses one electron, what is the resulting charge of the sodium ion? Write the equation for this process.

Accepted Answer

Positive; $$\mathrm{Na} \rightarrow \mathrm{Na}^+ + e^-$$

Question 5

Which of the following arrangements describes a group of spherical bacteria in grape-like clusters?

Accepted Answer

Staphylococcus

Question 6

A student accidentally overheats a bacterial smear during heat-fixing. What is the most likely consequence?

Accepted Answer

The bacterial cells may become distorted or lysed, making them difficult to observe.

Question 7

Which of the following best describes the chemical nature of a stain used in simple staining?

Accepted Answer

A salt in which one ion is colored (the chromophore) and the other is colorless.

Question 8

Which of the following is NOT a basic dye commonly used in microbiology?

Accepted Answer

Eosin

Question 9

A microbiologist is preparing a smear from a broth culture. Which step should be omitted compared to preparing a smear from a solid medium?

Accepted Answer

Adding a drop of water to the slide before transferring the culture.

Question 10

Which of the following best explains why acidic (anionic) stains are not used for direct staining of bacterial cells?

Accepted Answer

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

Question 11

Which of the following best describes the arrangement of Bacillus megaterium as seen under the microscope after simple staining?

Accepted Answer

Rod-shaped cells, often appearing singly or in chains.

Question 12

Which of the following equations correctly represents the formation of sodium chloride from its ions?

Accepted Answer

$$\mathrm{Na}^+ + \mathrm{Cl}^- \rightarrow \mathrm{NaCl}$$

Question 13

A student observes a slide under oil immersion and sees large, rod-shaped bacteria in chains. Which genus is most likely being observed?

Accepted Answer

Bacillus

Question 14

Which of the following is a correct step in the simple staining procedure for bacteria?

Accepted Answer

Flood the smear with methylene blue for 30–60 seconds.

Question 15

Which of the following best describes the value of a simple stain in microbiology?

Accepted Answer

It allows observation of the size, shape, arrangement, and morphology of microorganisms.

Question 16

Which of the following best explains the effect of methanol fixation on bacterial cells?

Accepted Answer

Methanol denatures proteins, causing the cells to adhere to the slide.

Question 17

Which of the following is a correct description of the arrangement 'streptobacilli'?

Accepted Answer

Chains of rod-shaped cells.

Question 18

A microbiologist is examining a stained slide and observes spherical cells arranged in pairs. What is the correct term for this arrangement?

Accepted Answer

Diplococcus

Question 19

Which of the following is a real-world application of the simple staining technique in clinical microbiology?

Accepted Answer

Rapid preliminary identification of bacterial morphology in patient samples.

Lab 5: Preparation of Smears and Simple Staining in Microbiology

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