Question 1

A microbe measures 10 μm in length. How long is this in nanometers (nm), and what group does it most likely belong to based on its size?

Accepted Answer

$$10\ \mu m = 10,000\ nm$$; most likely a protozoan

Question 2

What does it mean when a microscope has a resolution of $$0.2\ nm$$?

Accepted Answer

It can distinguish two points that are at least $$0.2\ nm$$ apart as separate objects.

Question 3

Why do electron microscopes have greater resolution than light microscopes?

Accepted Answer

Electrons have much shorter wavelengths than visible light, allowing for higher resolution.

Question 4

Why doesn’t a negative stain color a cell?

Accepted Answer

The dye is repelled by the negatively charged cell surface, staining the background instead.

Question 5

Why is the Gram stain so useful in microbiology?

Accepted Answer

It differentiates bacteria based on cell wall structure, aiding in diagnosis and treatment.

Question 6

Which step in the Gram stain procedure could be omitted and still allow differentiation between Gram-positive and Gram-negative cells?

Accepted Answer

The counterstain (safranin) step

Question 7

Using a compound light microscope with a resolving power of $$0.3\ \mu m$$, a $$10	imes$$ ocular lens, and a $$100	imes$$ oil immersion lens, would you be able to distinguish two objects separated by $$3\ \mu m$$?

Accepted Answer

Yes, because $$3\ \mu m \u003e 0.3\ \mu m ($$the resolving power).

Question 8

Why is it necessary to do an endospore stain to verify the presence of endospores, even though they can be seen as refractile structures in unstained cells?

Accepted Answer

Endospore stains specifically color endospores, confirming their identity and distinguishing them from other refractile bodies.

Question 9

A laboratory diagnosis of Neisseria gonorrhoeae infection is based on microscopic examination of Gram-stained pus. What is the disease caused by this bacterium?

Accepted Answer

Gonorrhea

Question 10

You are viewing a Gram-stained sample of vaginal discharge. Large (10 μm) nucleated red cells are coated with small (0.5 μm × 1.5 μm) blue cells. What is the most likely explanation for the red and blue cells?

Accepted Answer

Epithelial cells coated with bacteria, indicating bacterial vaginosis.

Question 11

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

Accepted Answer

Shorter wavelengths provide higher resolution.

Question 12

What unit is commonly used to measure the wavelength of visible light?

Accepted Answer

Nanometers (nm)

Question 13

Convert $$0.5\ \mu m to $$nanometers (nm).

Accepted Answer

$$0.5\ \mu m = 500\ nm$$

Question 14

Which of the following organisms is the smallest based on the provided size chart?

Accepted Answer

Viruses (20–250 nm)

Question 15

A student observes a sample under a light microscope and sees both purple cocci and pink rods. What does this indicate about the sample?

Accepted Answer

The sample contains both Gram-positive cocci and Gram-negative rods.

Question 16

Which of the following best explains why Chlamydia and Mycoplasma cannot be seen with a standard light microscope?

Accepted Answer

Their size (250 nm) is below the resolving power of light microscopes.

Question 17

In the clinical case of Maryanne, what was the causative agent of her peptic ulcer, and how was its presence confirmed?

Accepted Answer

Helicobacter pylori; confirmed by electron microscopy and Gram stain.

Question 18

Which of the following is a characteristic of Helicobacter pylori as described in the clinical case?

Accepted Answer

It is a Gram-negative, spiral-shaped bacterium associated with peptic ulcers.

Question 19

If you need to view a virus that is 100 nm in diameter, which microscope would you use and why?

Accepted Answer

Electron microscope, because its resolution is sufficient to distinguish objects smaller than 200 nm.

Chapter 3 Microbiology Study Guidance: Microscopy, Staining, and Microbial Classification

Study Guide - Practice Questions

Study Guide - Flashcards