Question 1

Which of the following best explains why electron microscopes have greater resolution than light microscopes?

Accepted Answer

Electrons have a shorter wavelength than visible light, allowing for finer detail to be distinguished. $$\lambda_{electron} \ll \lambda_{light}$$

Question 2

A microbiologist wants to observe live, unstained bacteria to study their motility. Which type of microscopy is most appropriate?

Accepted Answer

Darkfield light microscopy

Question 3

Which staining technique would you use to identify Mycobacterium tuberculosis in a sputum sample, and why?

Accepted Answer

Acid-fast staining, because Mycobacterium has a waxy cell wall containing mycolic acid.

Question 4

What is the main purpose of fixing a smear before staining?

Accepted Answer

To attach and kill microorganisms, preventing them from washing off during staining.

Question 5

Which of the following statements about Gram staining is correct?

Accepted Answer

Gram positive bacteria retain the crystal violet stain and appear purple, while Gram negative bacteria appear pink after counterstaining.

Question 6

A researcher wants to visualize the 3-D surface structure of a virus particle. Which microscopy technique should they use?

Accepted Answer

Scanning electron microscopy (SEM)

Question 7

Which of the following is a correct description of a simple stain?

Accepted Answer

Uses one dye to color all cells equally, such as methylene blue or safranin.

Question 8

Why is staining often necessary when using light microscopy to observe microorganisms?

Accepted Answer

Staining increases contrast between the microorganisms and the background, making structures more visible.

Question 9

Which of the following best describes the principle of phase contrast microscopy?

Accepted Answer

It uses special prisms to enhance contrast by amplifying differences in refractive index within the sample.

Question 10

A sample contains both Gram positive and Gram negative bacteria. After Gram staining, what colors would you expect to see under the microscope?

Accepted Answer

Gram positive bacteria would appear purple, Gram negative bacteria would appear pink.

Question 11

Which of the following is true regarding negative staining?

Accepted Answer

It stains the background, leaving the cells unstained and visible as clear areas.

Question 12

Which microscopy technique would be most suitable for visualizing the internal structure of a thin slice of a bacterial cell at very high resolution?

Accepted Answer

Transmission electron microscopy (TEM)

Question 13

Which of the following statements about endospore staining is correct?

Accepted Answer

Endospores are stained using malachite green and heat, followed by a water wash and safranin counterstain.

Question 14

Which formula correctly relates the resolution ($$d) of a $$microscope to the wavelength ($$\lambda) $$and the numerical aperture ($$NA) of $$the lens?

Accepted Answer

$$d = \frac{\lambda}{2NA}$$

Question 15

A scientist wants to observe the distribution of a specific protein within a cell. Which microscopy technique should they use?

Accepted Answer

Fluorescence microscopy with tagged antibodies specific to the protein.

Question 16

Which of the following is a key difference between light microscopy and electron microscopy?

Accepted Answer

Electron microscopy requires samples to be fixed and coated with heavy metals, often killing or altering the sample.

Question 17

Which of the following best describes the process of differential staining?

Accepted Answer

It uses two or more dyes to distinguish between different types of microorganisms based on their properties.

Question 18

Which microscopy technique allows for the deepest imaging into tissue with minimal damage, and is more expensive than confocal microscopy?

Accepted Answer

Two-photon microscopy

Question 19

A sample is stained with carbolfuchsin, decolorized with acid-alcohol, and counterstained with methylene blue. What type of bacteria will retain the carbolfuchsin stain?

Accepted Answer

Acid-fast bacteria, such as Mycobacterium spp.

Question 20

Which of the following is true about the visualization of viruses using microscopy?

Accepted Answer

Viruses, which range from 20-1000 nm, typically require electron microscopy for visualization due to their small size.

Microscopy and Staining in Microbiology: Principles, Types, and Applications

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