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 reduces light refraction, allowing more light to enter the objective lens and improving resolution.

Question 2

A microbiologist observes a specimen using a compound light microscope with a 40x objective lens and a 10x ocular lens. What is the total magnification?

Accepted Answer

$$40 	imes 10 = 400$$

Question 3

Which type of microscopy would be most appropriate for observing the three-dimensional surface structure of a virus particle?

Accepted Answer

Scanning electron microscopy (SEM)

Question 4

A bacterial cell is stained with crystal violet, treated with iodine, decolorized with alcohol, and then counterstained with safranin. If the cell appears pink under the microscope, what can you conclude about its cell wall?

Accepted Answer

It has a thin peptidoglycan layer and an outer membrane.

Question 5

Which of the following stains would be most appropriate for identifying Mycobacterium tuberculosis in a clinical sample?

Accepted Answer

Acid-fast stain

Question 6

Why are basic dyes, such as crystal violet and methylene blue, effective for staining bacterial cells?

Accepted Answer

Bacterial cells have a negative charge and attract the positively charged chromophore of basic dyes.

Question 7

A student prepares a smear, fixes it, and stains it with safranin only. What type of staining technique is this, and what information can be obtained?

Accepted Answer

Simple stain; reveals cell shape and arrangement.

Question 8

Which of the following best describes the main advantage of phase-contrast microscopy over brightfield microscopy?

Accepted Answer

It allows for the observation of living, unstained cells and their internal structures.

Question 9

During Gram staining, what is the primary function of the iodine step?

Accepted Answer

To act as a mordant and form a complex with crystal violet, making it less soluble.

Question 10

Which of the following statements about electron microscopy is correct?

Accepted Answer

Scanning electron microscopy (SEM) is used to view the surface of specimens in three dimensions.

Question 11

A microbiologist wants to visualize the presence of a gelatinous capsule surrounding a bacterial cell. Which staining technique should be used?

Accepted Answer

Negative staining with India ink or nigrosin

Question 12

Which of the following best explains why the resolving power of a microscope improves with shorter wavelengths of light?

Accepted Answer

Shorter wavelengths allow the microscope to distinguish between points that are closer together.

Question 13

Which of the following is a correct statement about the preparation of bacterial smears for staining?

Accepted Answer

Fixing the smear attaches the microorganisms to the slide and kills them.

Question 14

A clinical sample is stained using the Schaeffer-Fulton method. Green structures are observed inside red cells. What are these green structures?

Accepted Answer

Endospores

Question 15

Which of the following best describes the main 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 retain crystal violet, appearing purple.

Question 16

Which of the following is the correct order of steps in the Gram staining procedure?

Accepted Answer

Crystal violet, iodine, alcohol, safranin

Question 17

A scientist wants to observe the internal structures of a thin slice of a bacterial cell at very high magnification. Which microscope should be used?

Accepted Answer

Transmission electron microscope (TEM)

Question 18

Which of the following best describes negative staining?

Accepted Answer

It stains the background, leaving the cells colorless.

Question 19

Which of the following units would be most appropriate for measuring the size of a typical bacterial cell?

Accepted Answer

Micrometers ($$\mum)$$

Question 20

A sample contains both red blood cells and E. coli bacteria. Which microscope would allow you to see both cell types clearly, and why?

Accepted Answer

A compound light microscope, because both cell types are within its resolving power.

(Chapter 3) Observing Microorganisms Through a Microscope: Study Notes for Microbiology Students

Study Guide - Practice Questions

Study Guide - Flashcards