Q: Which of the following is a correct conversion based on the metric system used in microbiology?

$$1 \text{ mm} = 1000 \text{ \mu m}$$

Question 1

Which of the following best explains why immersion oil is used with the oil immersion objective lens in light microscopy?

Accepted Answer

It decreases the refractive index between the slide and the lens, reducing light loss.

Question 2

A microbiologist observes a living, unstained cell with clearly differentiated internal structures. Which type of microscopy is most appropriate for this observation?

Accepted Answer

Phase-contrast microscopy

Question 3

Calculate the total magnification of a specimen viewed with a 40x objective lens and a 10x ocular lens.

Accepted Answer

$$40 	imes 10 = 400$$

Question 4

Which of the following statements about electron microscopy is correct?

Accepted Answer

It provides greater resolution due to the shorter wavelength of electrons.

Question 5

A bacterial sample is stained with crystal violet, treated with iodine, washed with alcohol, and counterstained with safranin. After this procedure, some cells appear pink and others purple. What does this indicate?

Accepted Answer

The sample contains both gram-positive and gram-negative bacteria.

Question 6

Which microscopy technique would be most suitable for visualizing the three-dimensional surface structure of a bacterial cell?

Accepted Answer

Scanning electron microscopy

Question 7

A scientist wants to identify Mycobacterium tuberculosis in a sputum sample. Which staining technique should be used?

Accepted Answer

Acid-fast stain

Question 8

Which of the following best describes the principle of fluorescence microscopy?

Accepted Answer

It uses UV light to excite fluorochromes, which emit visible light.

Question 9

Which of the following is a correct conversion based on the metric system used in microbiology?

Accepted Answer

$$1 	ext{ mm} = 1000 	ext{ \mu m}$$

Question 10

Which staining method is specifically used to visualize bacterial capsules?

Accepted Answer

Negative staining with India ink or nigrosin

Question 11

A researcher needs to study the arrangement of DNA molecules at near-atomic resolution. Which microscopy technique should be used?

Accepted Answer

Scanning tunneling microscopy

Question 12

Which of the following best explains why basic dyes are commonly used to stain bacterial cells?

Accepted Answer

Bacterial cells are negatively charged and attract the cationic chromophore of basic dyes.

Question 13

Which microscopy technique would be most appropriate for examining living cells attached to a surface, such as a biofilm?

Accepted Answer

Scanning acoustic microscopy

Question 14

Which of the following is a key difference between Gram-positive and Gram-negative bacteria as revealed by the Gram stain?

Accepted Answer

Gram-positive bacteria have a thick peptidoglycan layer and appear purple.

Question 15

Which of the following best describes the purpose of a mordant in staining procedures?

Accepted Answer

To increase the affinity of the stain for the specimen

Question 16

A sample is stained with malachite green and safranin. Green structures are seen inside red cells. What are these green structures?

Accepted Answer

Endospores

Question 17

Which microscopy technique uses two photons of long-wavelength light to excite fluorochromes and can image living cells up to 1 mm deep?

Accepted Answer

Two-photon microscopy

Question 18

Which of the following is a major advantage of differential interference contrast (DIC) microscopy over phase-contrast microscopy?

Accepted Answer

DIC microscopy provides colored, three-dimensional images.

Question 19

A clinical laboratory is testing for the presence of bacterial flagella. Which staining method should be used?

Accepted Answer

Flagella stain with a mordant and carbolfuchsin

Question 20

Which of the following best describes the main limitation of brightfield microscopy when observing viruses?

Accepted Answer

Viruses are too small to be resolved due to the wavelength of visible light.

Chapter 3 - Observing Microorganisms Through a Microscope: Principles and Techniques

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