Question 1

Which type of microscope does not use light in forming the specimen image?

Accepted Answer

Electron microscopes use a beam of electrons instead of light to form an image of the specimen, making it the only option listed that does not use light.

Question 2

Fixed smears of specimens are required to perform the Gram stain or the endospore stain.

Accepted Answer

Fixed smears are necessary for both the Gram stain and the endospore stain to properly visualize and differentiate bacterial structures.

Question 3

Comparing transmission electron microscopy with scanning electron microscopy, the following statement is true.

Accepted Answer

Transmission electron microscopy is used to study the internal details of cells and subcellular structures. Scanning electron microscopy, on the other hand, is used to study the external architecture of cells. Transmission electron microscopy does not necessarily require dyes, as structures can be visualized using electron-dense staining techniques. Both transmission and scanning electron microscopy can provide good images of bacteria and viruses.

Question 4

Which type of microscope achieves the greatest resolution and highest magnification?

Accepted Answer

Electron microscopes use a beam of electrons instead of light to visualize samples. This makes it possible to achieve much higher magnifications and resolutions, allowing for the observation of structures and details at the subcellular and molecular levels.

Question 5

The Gram staining procedure is best described as a ______ staining technique.

Accepted Answer

The Gram staining procedure is a differential staining technique, as it differentiates bacteria based on the properties of their cell walls. The stain allows for the identification of gram-positive and gram-negative bacteria, which have different cell wall compositions. Therefore, option D is the correct answer. The other options (negative, simple, and selective) do not accurately describe the Gram staining procedure.

Question 6

Which type of microscope cannot image live specimens?

Accepted Answer

Electron microscopes use beams of electrons to create images and cannot be used to image live specimens.

Question 7

Following a properly-performed Gram stain, gram-positive bacteria will appear as pink or red cells.

Accepted Answer

Following a properly-performed Gram stain, gram-positive bacteria will appear as purple cells, not pink or red. Gram-negative bacteria will appear as pink or red.

Question 8

A differential interference contrast microscope uses dyes to give colored, three-dimensional images.

Accepted Answer

A differential interference contrast microscope uses differences in refractive index to produce a three-dimensional image, and does not require the use of dyes.

Question 9

Basic dyes are

Accepted Answer

Basic dyes are cationic and are attracted to the negatively charged acidic surface of bacterial cells, which makes them ideal for staining these cells. Basic dyes bind to the cells and make them visible under the microscope.

Question 10

The bending of light rays as they pass from one medium to another is called refraction.

Accepted Answer

Refraction is the bending of light rays as they pass from one medium to another due to a change in their speed.

Question 11

The purpose of staining cells on a microscope slide is to ______.

Accepted Answer

The purpose of staining cells on a microscope slide is to add contrast to the cells so they can be seen better under the microscope.

Question 12

Which type of microscope bombards a whole, metal-coated specimen with electrons moving back and forth over it?

Accepted Answer

Scanning electron microscope (SEM) bombards a whole, metal-coated specimen with electrons moving back and forth over it, producing a detailed 3D image of the specimen's surface.

Question 13

A microbiologist makes a fixed smear of bacterial cells and stains it with methylene blue.All cells appear blue under the oil immersion lens.This is an example of ______.

Accepted Answer

This is an example of simple staining as only one dye (methylene blue) was used to stain the bacterial cells and all cells appear blue under the oil immersion lens. In negative staining, cells would appear colorless while the background would be stained. Capsule staining and acid-fast staining are specific types of staining used to visualize certain structures or characteristics of bacterial cells. Using an acidic dye may or may not result in all cells appearing the same color, depending on the type of stain and the cellular structures being visualized.

Question 14

What do the Gram stain, the acid-fast stain, and the endospore stain have in common?

Accepted Answer

The Gram stain, acid-fast stain, and endospore stain are all differential stains, which means they allow differentiation between different types of microorganisms based on the staining outcome. The Gram stain differentiates between Gram-positive and Gram-negative bacteria, the acid-fast stain is used to detect mycobacteria, and the endospore stain is used to distinguish between endospores and vegetative cells. The other options are not true for all three stains, as not all of them require heat, charge of the cell wall may not always affect staining outcome, and some may not be used on a wet mount. Negative stain technique is not used for any of the three stains.

Quiz 3: Tools of the Laboratory: Methods for the Culturing of Microscopic Analysis of Microorganisms