Chapter 3 Study Guide

How many nanometers is 10 μm?

10 μm is 10,000 nm.

Through what lenses does light pass in a compound microscope?

Light passes through the objective lens and ocular lens.

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

It can distinguish two points that are 0.2 nm apart.

How are brightfield, darkfield, phase-contrast, and fluorescence microscopy similar?

They all use visible light to view specimens.

Why do electron microscopes have greater resolution than light microscopes?

They use shorter wavelengths than light microscopes.

For what is a Transmission Electron Microscope (TEM) used?

It is used to study thin sections of organisms.

For what is a Scanning Electron Microscope (SEM) used?

It is used to view the surface of whole microorganisms.

For what is Scanned-Probe Microscopy used?

It is used to produce three-dimensional images of surfaces.

Why doesn’t a negative stain color a cell?

The stain only colors the background, not the cells.

Why is fixing necessary for most staining procedures?

It kills and attaches microorganisms to the slide.

Why is the Gram stain so useful?

It differentiates bacteria based on their cell wall composition.

Which stain would be used to identify microbes in the genera Mycobacterium and Nocardia?

The Acid-fast stain.

How do unstained endospores appear?

They appear clear, colorless, and indistinct.

How do stained endospores appear?

They appear green or blue.

The most common microscope used in microbiology is the:

Compound light microscope.

The total magnification of an object is calculated by:

Multiplying the magnification of the objective lens by the ocular lens.

The compound light microscope uses:

Visible light for magnification.

The maximum resolution (or resolving power) of a compound light microscope is:

0.2 μm.

The maximum magnification of a compound light microscope is:

1,500x.

Specimens are stained to:

Make them visible under a microscope.

Immersion oil is used with the oil immersion lens to:

Reduce light loss between the slide and the lens.

Brightfield illumination is used for:

Viewing stained smears.

Unstained cells are more productively observed using which type of microscopy?

Darkfield, phase-contrast, or DIC microscopy.

The darkfield microscope shows:

A light silhouette of an organism against a dark background.

A phase-contrast microscope allows for:

Detailed observation of living organisms without staining.

In fluorescence microscopy, specimens are first stained with:

Fluorochromes.

Fluorescence microscopy is primarily used in:

The fluorescent-antibody (FA) technique.

Instead of light, a beam of ________ is used with an electron microscope.

Electrons.

Instead of glass lenses, electron microscopes use ________ to control focus, illumination, and magnification.

Electromagnets.

Thin sections of organisms can be seen in an electron micrograph produced using a:

Transmission electron microscope (TEM).

Three-dimensional views of the surfaces of microorganisms can be obtained with:

Scanning electron microscope (SEM).

A smear is:

A thin film of material used for microscopic examination.

A mordant may be used in a staining procedure to:

Improve bonding between the stain and the specimen.

Differential stains, such as the Gram stain, are used to:

Differentiate bacteria according to their reactions to stains.

The Gram stain uses which of the following as a mordant?

Iodine.

Gram-positive bacteria remain ________ after the decolorization step of the Gram stain.

Purple.

Which of the following bacteria appears red after an acid-fast stain?

Mycobacterium tuberculosis.

A negative stain is used to make ________ visible.

Microbial capsules.

Endospore staining is used to visualize:

Endospores.

Flagella staining is used to visualize:

Flagella.

Which of the following is a characteristic of electron microscopes?

Use electromagnets instead of glass lenses.