Chapter 2 Microbiology

Which of the following stains would best determine if a bacterium has a single cell membrane plus a very thick cell wall or if a bacterium has a very thin cell wall in between two cell membranes?

Gram-stain

If the objective lenses of a microscope can be changed without losing focus on the specimen, they are said to be _________.

Parfocal

The Gram stain can only be performed on cultures grown in liquid media.

False

Which of the following microscopes typically uses dyes or antibodies?

Florescence Microscope

How does the addition of immersion oil provide better magnification than a high power lens alone?

The immersion oil has the same refractive index as glass; by placing a drop of oil between the glass slide and the lens, this eliminates two refractive surfaces. The immersion oil used has a higher refractive index than the objective lens used, thus causing more light rays to be bent.

Review the functions of various parts of the bright-field microscope by placing each term in the correct sentence.

The ocular lens magnifies an image produced by the objective lens to produce a virtual image. Objective lenses are contained in a nosepiece that can be turned to put a particular objective lens in place to be used. The iris diaphragm is a type of shutter found under the stage of many microscopes that can be used to adjust the light intensity on the specimen. Slides containing specimens are mounted on the stage of the microscope. An objective lens gathers light from a specimen and focuses it to produce a real image.

What would be the best technique to prepare and view the internal structures of fungal hyphae?

Transmission electrom microscopy

A substage condenser is used to focus light onto the specimen, which increases the resolution of a light microscope.

True

Acetone can be used as the decolorizer in the Gram stain procedure.

True

Light rays are refracted (bent) when they cross the interface between materials with different refractive indices.

True

The proper sequence of reagents in the Gram stain procedure is _________.

crystal violet, iodine, ethanol, safranin

Basic dyes such as methylene blue bind to cellular molecules that are __________.

negatively charge

Immersion oil can be used to increase the resolution achieved with some microscope lenses because it increases the __________ between the specimen and the objective lens.

refractive index

What microscope would be the best to use to view cell surface features of a specimen?

scanning electron

A lens with a ________ focal length should have a greater magnification.

short

Immersion oil increases the amount of light entering the objective lens.

true

A 45× objective and a 10× ocular produce a total magnification of ________.

450x

A 30× objective and a 20× ocular produce a total magnification of ________.

600x

Acid-fast organisms such as Mycobacterium tuberc

Lipids

After performing a Gram stain of a mixed culture of Gram-positive and Gram-negative cells, you realize you forgot to apply the iodine in step 2. What would you expect to see if you observed the slide under the microscope after this omission?

Pink Gram-positive and pink Gram-negative cells

After the decolorizer has been added, Gram-positive organisms are stained __________ and Gram-negative organisms are stained __________.

Purple; colorless

Drag the labels to complete each of the sentences that discuss the importance of appropriate fixation methods for microscopic observation of specimens

When preparing specimens for microscopic observation, it is important to preserve the internal and external structures so they resemble living cells as much as possible. During the fixation process, cells are killed and adhered firmly to the slide so they do not wash off during the staining process. There are two main methods for fixing cells to a slide; heat fixation and chemical fixation. Heat fixation is valuable in that it preserves the overall morphology of the specimen; however, it also distorts internal structures. Chemical fixation preserves the integrity of the cellular substructures as well as the morphology. Chemical fixation is often used for eukaryotes, particularly with the use of electron microscopes, whereas heat fixation is typically used when observing bacteria and archaeon with a light microscope, since it is easy and adequate.

The Gram stain of a bacterial cell is based on the chemical properties of its ________.

cell wall

As the magnification on a bright-field microscope increases, the amount of light that reaches the eye ________.

decreases

The Gram-staining procedure is an example of __________.

differential staining