Question 1

Which of the following best explains why electron microscopes have a higher resolving power than light microscopes?

Accepted Answer

Electrons have a shorter wavelength than visible light, allowing for greater resolution.

Question 2

A microbiologist wants to observe the internal structures of a living, unstained cell. Which type of microscopy should they use?

Accepted Answer

Phase-contrast microscopy

Question 3

What is 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 staining technique would you use to differentiate between Mycobacterium tuberculosis and Staphylococcus aureus?

Accepted Answer

Acid-fast stain

Question 5

During Gram staining, what is the primary reason Gram-negative bacteria appear pink after the procedure?

Accepted Answer

Their thin peptidoglycan layer allows the crystal violet-iodine complex to be washed out by alcohol, so they retain the safranin counterstain.

Question 6

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

Accepted Answer

It increases the affinity of the stain for the specimen by forming a complex with the dye.

Question 7

A scientist wants to visualize the three-dimensional surface structure of a virus. Which microscopy technique should they use?

Accepted Answer

Scanning electron microscopy (SEM)

Question 8

Which of the following statements about fluorescence microscopy is correct?

Accepted Answer

It uses ultraviolet light to excite fluorochromes, which then emit visible light.

Question 9

Why is immersion oil used with the 100x objective lens in light microscopy?

Accepted Answer

It increases the refractive index between the specimen and the lens, reducing light loss and improving resolution.

Question 10

Which of the following best explains why negative staining is useful for observing bacterial capsules?

Accepted Answer

Capsules do not readily take up most stains, so staining the background makes the capsule visible as a clear halo.

Question 11

A sample is stained with carbolfuchsin, treated with acid-alcohol, and then counterstained with methylene blue. Acid-fast bacteria will appear:

Accepted Answer

Red

Question 12

Which of the following is a key advantage of confocal microscopy over traditional fluorescence microscopy?

Accepted Answer

It allows for the construction of three-dimensional images by scanning multiple planes of the specimen.

Question 13

A microbiologist observes a specimen using darkfield microscopy. What is the appearance of the specimen and background?

Accepted Answer

The specimen appears bright against a dark background.

Question 14

Which of the following best describes the relationship between wavelength and resolution in microscopy?

Accepted Answer

Resolution increases as wavelength decreases.

Question 15

A student prepares a bacterial smear and stains it with a basic dye. What is the charge on the chromophore of the dye, and why does it bind to the bacterial cell?

Accepted Answer

The chromophore is a cation, which binds to the negatively charged bacterial cell surface.

Question 16

Which of the following is NOT a type of light microscopy?

Accepted Answer

Transmission electron microscopy

Question 17

A hospital laboratory receives a sputum sample suspected of containing Mycobacterium tuberculosis. Which staining protocol should be used to confirm the diagnosis?

Accepted Answer

Acid-fast stain

Question 18

Which of the following best describes the main difference between simple and differential stains?

Accepted Answer

Simple stains use one dye to highlight the entire organism, while differential stains use multiple dyes to distinguish between organisms or structures.

Question 19

A researcher wants to observe the layers of a biofilm up to 100 μm deep. Which microscopy technique should they use?

Accepted Answer

Confocal microscopy

Question 20

Which of the following best explains why live, unstained specimens are often difficult to observe with brightfield microscopy?

Accepted Answer

They have little contrast with the surrounding medium.

Observing Microorganisms Through a Microscope: Principles and Techniques

Study Guide - Practice Questions

Study Guide - Flashcards