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 growth 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.

Question 4

If too much heat is applied during heat-fixing, what is the most likely consequence?

Accepted Answer

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

Question 5

Which of the following equations correctly represents the formation of sodium chloride (NaCl) via ionic bonding?

Accepted Answer

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

Question 6

Which of the following best describes the arrangement of Staphylococcus cells as seen under the microscope after simple staining?

Accepted Answer

Grape-like clusters of spherical cells

Question 7

A student prepares a smear from a broth culture of Bacillus megaterium. What is the correct procedure for transferring the culture to the slide?

Accepted Answer

Transfer 2–3 loopfuls of the broth directly onto the slide without adding water.

Question 8

Which of the following is NOT a basic dye used in simple staining?

Accepted Answer

Eosin

Question 9

Why are acidic (anionic) stains generally not used for direct staining of bacterial cells?

Accepted Answer

Their negatively charged chromophores are repelled by the negatively charged bacterial cell surface.

Question 10

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 11

A student observes a slide under oil immersion and sees rod-shaped cells arranged in chains. Which term best describes this arrangement?

Accepted Answer

Streptobacilli

Question 12

Which of the following statements about the genus Bacillus is correct?

Accepted Answer

Members of the genus Bacillus are spore-forming and can survive in harsh environments.

Question 13

Which of the following best explains why methanol can be used to fix a bacterial smear?

Accepted Answer

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

Question 14

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

Accepted Answer

Prepare smear, air-dry, heat-fix, apply stain, rinse, blot dry, examine

Question 15

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 (chromophore)

Question 16

A student accidentally skips the heat-fixing step before staining. What is the most likely result?

Accepted Answer

The bacterial cells may be washed off the slide during the staining process.

Question 17

Which of the following arrangements is characteristic of Streptococcus species?

Accepted Answer

Chains of spherical cells

Question 18

Which of the following best describes the charge on a bacterial cell surface and its relevance to staining?

Accepted Answer

Bacterial cells are negatively charged, which attracts positively charged (basic) stains.

Question 19

Which of the following is a correct statement about the use of oil immersion in microscopy?

Accepted Answer

Oil immersion increases the resolving power of the microscope by reducing light refraction.

Question 20

Which of the following best describes the arrangement known as 'sarcinae'?

Accepted Answer

Cubes of 8 spherical cells (2×2×2)

Preparation of Smears and Simple Staining in Microbiology

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