Question 1

Which of the following best explains why oil is used with the oil immersion lens in light microscopy?

Accepted Answer

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

Question 2

A microbiologist is trying to observe the ultrastructure of a virus particle. Which microscope and magnification range should they use?

Accepted Answer

Transmission electron microscope (TEM), 10,000X to 100,000X

Question 3

Which of the following statements about Gram staining is correct?

Accepted Answer

The decolorizing agent breaks down the thin cell wall of Gram-negative bacteria, allowing the primary stain and mordant to wash away.

Question 4

A student observes a specimen that appears light against a dark background. Which type of microscopy is being used?

Accepted Answer

Dark-field microscopy

Question 5

Why do modern light microscopes have a better resolving power than Leeuwenhoek’s original microscope?

Accepted Answer

They use light with shorter wavelengths and lenses that gather light more efficiently.

Question 6

Which of the following best describes a negative stain?

Accepted Answer

An acidic dye that stains the background but leaves the cells colorless due to repulsion by the cell surface.

Question 7

A microbiologist wants to distinguish between two points that are 0.15 $$\mum $$apart. Which microscope should they use, based on resolving power?

Accepted Answer

An electron microscope, since modern light microscopes have a resolving power of about 0.2 $$\mum.$$

Question 8

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

Accepted Answer

Crystal violet, mordant, decolorizing agent, safranin

Question 9

A scientist is using a confocal microscope. What is the main advantage of this technique?

Accepted Answer

It uses lasers to illuminate fluorescent chemicals, producing sharp, three-dimensional images.

Question 10

Which of the following best explains why a mordant is used in staining procedures?

Accepted Answer

It binds to a dye, making it less soluble and helping it adhere to the specimen.

Question 11

A clinical sample is suspected to contain encapsulated bacteria. Which staining technique would best reveal the presence of a capsule?

Accepted Answer

Negative staining, which leaves the capsule as a clear halo around the cell.

Question 12

Which of the following is NOT a correct match between the microscope type and its primary use?

Accepted Answer

SEM: electrons pass through the specimen to reveal internal structures.

Question 13

A microbiologist is classifying bacteria based on their ability to ferment carbohydrates and produce hydrogen sulfide gas ($$\mathrm{H_2S}). $$Which type of classification is being used?

Accepted Answer

Biochemical characteristics

Question 14

Which of the following statements about the use of stains in microscopy is correct?

Accepted Answer

Stains are salts in which one of the ions is colored and can bind to cellular structures via covalent, ionic, or hydrogen bonds.

Question 15

A sample is prepared by making a thin film of organisms on a slide, then fixing it with heat. What is this preparation called?

Accepted Answer

A smear

Question 16

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

Accepted Answer

Shorter wavelengths of light result in higher resolution.

Question 17

A scientist is analyzing a bacterial population that arose from a single cell and shows unique antigenic properties. What is the correct term for this population?

Accepted Answer

Strain (serotype)

Question 18

Which of the following is a real-world application of phase-contrast microscopy?

Accepted Answer

Observing living, unstained cells to study their internal structures and motility.

Question 19

Which of the following is a correct statement about the use of objective lenses in light microscopy?

Accepted Answer

The objective lens is a series of lenses that gathers and focuses light to form a magnified image.

Question 20

A laboratory technician is tasked with identifying bacteria based on differences in their fatty acid compositions. This method is most closely related to which classification approach?

Accepted Answer

Biochemical classification

Microscopy, Staining, and Classification: Study Notes

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