Q: A student wants to convert 2 mm to μm. What is the correct calculation?

$$2 \times 1000 = 2000$$ \mu m$

Question 1

A microbe measures 10 μm in length. How long is this in nanometers (nm) and millimeters (mm)?

Accepted Answer

$$10,000 nm$; 0.01 mm$$

Question 2

Which group would a 10 μm long microbe most likely belong to, based on the size chart provided?

Accepted Answer

Protozoa

Question 3

A microscope has a resolution of $$0.2 nm. $$What does this mean?

Accepted Answer

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

Question 4

Why do electron microscopes have greater resolution than light microscopes?

Accepted Answer

Electrons have much shorter wavelengths than visible light.

Question 5

Why doesn’t a negative stain color a cell?

Accepted Answer

The dye is repelled by the negatively charged cell surface.

Question 6

Why is the Gram stain so useful in microbiology?

Accepted Answer

It differentiates bacteria based on cell wall structure.

Question 7

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

Accepted Answer

Counterstain (safranin)

Question 8

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

Accepted Answer

Yes, because the separation equals the resolving power.

Question 9

Endospores can be seen as refractile structures in unstained cells and as colorless areas in Gram-stained cells. Why is an endospore stain necessary to verify their presence?

Accepted Answer

Endospore stains specifically color endospores, confirming their identity.

Question 10

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 11

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?

Accepted Answer

Epithelial cells coated with bacteria (clue cells), indicating bacterial vaginosis.

Question 12

Which of the following is the correct order of size from largest to smallest?

Accepted Answer

Protozoa \u003e Bacteria \u003e Viruses

Question 13

What characteristic of light is most important for the resolution of a microscope?

Accepted Answer

Wavelength

Question 14

How do you measure the wavelength of light?

Accepted Answer

Distance between two consecutive peaks or troughs

Question 15

Which unit is used to measure the wavelength of visible light?

Accepted Answer

Nanometers (nm)

Question 16

A student wants to convert 2 mm to μm. What is the correct calculation?

Accepted Answer

$$2 	imes 1000 = 2000$$ \mu m$

Question 17

Which of the following best explains why oil immersion increases the resolving power of a light microscope?

Accepted Answer

It reduces light refraction, allowing more light to enter the objective lens.

Question 18

Which of the following is NOT a characteristic of Helicobacter pylori as described in the clinical case?

Accepted Answer

It is a protozoan.

Question 19

A light microscope with a resolving power of $$0.3$$ μm is used to view two objects separated by $$300 nm. $$Will they appear as separate objects?

Accepted Answer

No, because $$300 nm is $$less than the resolving power.

Chapter 3 Microbiology: Microscopy, Staining, and Microbial Size Study Guide

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