Question 1

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

Accepted Answer

Electron beams have much shorter wavelengths than visible light.

Question 2

A researcher wants to observe the surface structure of a pollen grain in three dimensions. Which microscopy technique should they use and why?

Accepted Answer

Scanning electron microscopy (SEM), because it scans the specimen’s surface with electrons.

Question 3

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

Accepted Answer

Acid-fast stain

Question 4

Why are basic dyes more commonly used than acidic dyes for staining bacterial cells?

Accepted Answer

Bacterial cell walls are negatively charged and attract the cationic chromophores of basic dyes.

Question 5

A microbiologist observes unstained, living cells moving under a microscope. Which type of microscopy is most likely being used?

Accepted Answer

Phase-contrast light microscopy

Question 6

Which of the following is a primary purpose of heat-fixing a bacterial smear before staining?

Accepted Answer

To kill and adhere the organisms to the slide

Question 7

A clinical laboratory uses a dichotomous key to identify an unknown bacterium. What is the main advantage of this approach?

Accepted Answer

It provides a systematic method for narrowing down the identity based on observable traits.

Question 8

Which of the following statements about Gram staining is correct?

Accepted Answer

Gram-positive bacteria appear purple because their thick peptidoglycan layer retains the crystal violet-iodine complex.

Question 9

Which of the following best describes the main difference between SEM and TEM?

Accepted Answer

SEM provides 3D images of surfaces, while TEM provides 2D images of internal structures.

Question 10

A scientist is using MALDI-TOF mass spectrometry to identify a bacterial isolate. What is the principle behind this technique?

Accepted Answer

It analyzes the unique protein fingerprint of the organism.

Question 11

Which of the following is NOT a component of Linnaeus’s system of taxonomy?

Accepted Answer

Domain

Question 12

Carl Woese’s classification of life into three domains was based primarily on differences in which molecule?

Accepted Answer

16S ribosomal RNA

Question 13

Which staining technique would be most useful for visualizing bacterial capsules?

Accepted Answer

Negative stain

Question 14

A sample is stained with malachite green and safranin. Endospores appear green and vegetative cells appear pink. Which staining method was used?

Accepted Answer

Endospore stain

Question 15

Which of the following best explains why the Gram stain is considered a differential stain?

Accepted Answer

It uses more than one dye to distinguish between different types of bacteria.

Question 16

A clinical sample is tested using a serological assay. What is being detected in this type of test?

Accepted Answer

The presence of specific antigens or antibodies

Question 17

Which of the following is a key advantage of using probe microscopy (such as STM or AFM) over electron microscopy?

Accepted Answer

Probe microscopy can visualize living cells in aqueous environments.

Question 18

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

Accepted Answer

A mordant increases the affinity of the stain for the specimen.

Question 19

A laboratory is using phage typing to identify a bacterial strain. What is the basis of this technique?

Accepted Answer

The susceptibility of bacteria to specific bacteriophages

Question 20

Which of the following equations correctly relates the resolving power ($$d) of a $$microscope to the wavelength ($$\lambda) of $$light and the numerical aperture ($$NA) of $$the lens?

Accepted Answer

$$d = \frac{0.61 	imes \lambda}{NA}$$

Microscopy, Staining, and Classification in Microbiology

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