Mastering Microbiology Chapter 4

What is the role of lenses in microscopy? Lenses increase the contrast to determine structural differences in stained specimens. Lenses are only used to magnify specimens that are smaller than whole red blood cells. Lenses focus either light or electrons to create a magnified image of a specimen.

Why do electron microscopes have higher resolving power than light microscopes? The copper grid used in electron microscopy provides enhanced resolution. The fluorescent screen adds another magnification step. They are capable of producing 3-dimensional images, which light microscopes cannot do. Electrons have a smaller wavelength than visible light, leading to higher resolution.

Which of the following is a lens found on electron microscopes but not on light microscopes? Projector lens Eyepiece lens Objective lens Condenser lens

Which type of microscope would allow the viewer to see ribosomes inside a cell? A light microscope A light microscope, transmission electron microscope, and scanning electron microscope can all view ribosomes inside a cell. A transmission electron microscope A scanning electron microscope

Which of the following is a characteristic shared by both electron and light microscopes? They both employ the use of objective lenses. They both utilize white light to magnify the specimen. Both microscopes have a resolving power of 0.01 nm. Both microscopes require an internal camera to visualize the specimen.

What is the fate of the electrons that interact with a specimen in an electron microscope? They are refracted by the specimen. They may be absorbed, reflected, or refracted by the specimen. They are absorbed by the specimen. They are reflected by the specimen.

Why is a specimen smaller than 200 nm not visible with a light microscope? It is too easy to lose on the stage. Anything smaller than 200 nm cannot interact with visible light. The lenses only go to 100 X magnification power. Visible light is only good at wavelengths below 390 nm.

What happens to the light rays when they hit the specimen? They are diverted to the ocular lens. They are focused into a small area towards the objective lens. They are absorbed by the stage. They are reflected, refracted, or absorbed by the specimen.

What is the role of the ocular lens? To adjust the wavelength of light To do the bulk of the magnification To recreate the image in the viewer's eye To focus the light to a high intensity in a small area

What is meant by light rays being divergent? It is coming together to a focused beam It is spreading out It is heading upwards

In a typical brightfield microscope (seen in the animation), at which point does magnification begin? The ocular lens The lamp The stage The objective lens The condenser lens

While staining a mixed culture of Gram-positive and Gram-negative bacteria, switching the order of steps 2 and 3 would result in ______________________. all bacteria appearing pink all bacteria appearing clear a change in the Gram reaction; Gram-negative cells would appear purple while Gram-positive cells would appear pink. all bacteria appearing purple

Which structural feature of Gram-positive bacteria enhances their ability to retain the crystal violet dye? an outer membrane a thick peptidoglycan layer a thin peptidoglycan layer All of the above contribute to a Gram-positive cell's ability to retain crystal violet.

What would you anticipate seeing if you accidentally switched crystal violet and safranin while performing a Gram stain? Gram-positive bacteria would appear purple and Gram-negative bacteria would appear pink. All bacteria would appear purple. Gram-positive bacteria would appear pink and Gram-negative bacteria would appear purple. All bacteria would appear pink.

What would you expect to see if you forgot to perform step 2 of the Gram stain procedure? Gram-positive cells would appear pink and Gram-negative cells would appear purple. All bacteria would appear pink. All bacteria would appear purple. Gram-positive cells would appear purple and Gram-negative cells would appear pink.

How are negative stains different from other types of stains? They stain the desired structure or specimen black. They stain more than one type of specimen. They stain the background, leaving the cells colorless.

Which of the following is an example of a dye used in a simple stain? Eosin Carbolfuchsin Nigrosin Methylene blue

How does the malachite green stain enter an endospore? It is mixed with the mordant tannic acid. It is dissolved in alcohol. It is heated. It is mixed with hydrochloric acid.

Following an endospore stain, how does one distinguish endospores from vegetative cells? Vegetative cells are green, endospores are pink. Vegetative cells are purple, endospores are pink. Vegetative cells are pink, endospores are purple. Vegetative cells are pink, endospores are green

What is the fundamental purpose of staining in light microscopy? To see the specimen without the aid of a microscope To kill the specimen To increase the contrast and visibility of the specimen To make the specimen appear larger in the microscope

A student from one of the research labs is having trouble preparing a slide for examination and photographing. The bacterial slide that he has brought to you was prepared using a commercially purchased stain. He has asked for your help in determining what he is doing wrong so that he can change the lab protocols and continue on with his project. After examining the slide under oil immersion, you determine that no bacteria are present even though the student is able to show you the culture he used to make that slide that has visible growth in the liquid medium. Which of the following statements does NOT explain the fact that there are no bacteria present on the student's slide?

You volunteer to help the student with his fixation technique and in choosing a proper stain for the project he is working on. After watching and helping the student correct any problems with his fixation technique, you now need to determine which stains to use. The single criterion for the project is to be able to determine cell shape and size in a pure broth culture after some treatments. No differentiation between cell types is required (i.e., Gram-positive or Gram-negative), so you want to convince the student that a simple stain would be his best option. The charged dyes used in simple staining will penetrate the bacterial cell and will be retained after rinsing the slide with water to remove surplus dye. Which staining procedure would be best to use to stain the slides required for this student's project? Why?

You have been asked to lead a demonstration for the undergraduate microbiology lab course about the uses of negative staining when studying bacteria. A "negative" stain does not stain the bacterial cell itself but stains the space between cells. Under magnification, the acidic (negatively charged) nature of the stain will be repelled by the negatively charged bacterial cell wall and will leave the cell colorless in a stained background. Negative stains are used primarily to reveal the presence of negatively charged bacterial capsules; therefore, they are also called capsule stains. Encapsulated cells appear to have a halo surrounding them. The negative stain procedure does not require heat fixation, which limits any chances of alteration in bacterial cell shape and size. The bacterial suspension is added to a drop of stain, such as nigrosin or eosin, and drawn across the glass slide using a coverslip. Nigrosin staining-not safranin staining-of Klebsiella pneumoniae will allow for the visualization of the cell shape and the determination of the presence of a capsule.

Why is visualization not sufficient to properly identify bacteria? Bacteria have a limited set of shapes and many unrelated bacteria share the same shape. Bacteria have a limited set of shapes. Not all bacteria can be seen with a light microscope. Many unrelated bacteria can share the same shape. Identification is only needed in clinical specimens.

What is the hallmark of dichotomous keys? They are open-ended questions. They only relate to the shape of the cell. They only relate to biochemical processes of the cell. They consist of a series of paired statements, in which only one statement of each pair applies to a given organism.

Biochemical tests _________________. are the most effective way to determine bacterial shape are the main methods used to identify unknown bacteria are used to determine rate of growth are visualized using microscopes

Why is the unknown in this example not Pseudomonas? It is a Gram-negative cell. It can tolerate oxygen. It ferments lactose. It is a rod-shaped cell.

What test result indicates that the unknown can utilize citrate as its sole carbon source? It turns the medium black. The medium turns blue. The culture becomes turbid. The medium turns pink.

How would the results be different if this organism was Salmonella? It would produce hydrogen sulfide. It would not tolerate oxygen. It would not ferment lactose. It would be a rod.

How is fermentation of lactose detected? The acetoin produced turns the medium pink. The cells form a black precipitant. The drop in pH turns the indicator dye yellow. The medium become turbid when exposed to air.

How many questions are needed in this dichotomous key to determine if the unknown is Bacteroides? Five Two Three Four

How many answers are there to a question in a dichotomous key flowchart? Any number of answers are possible. Three Four Two

Why are flowcharts useful for dichotomous keys? They allow the researcher to get the answer without having to do many tests. They allow the researcher to visualize relationships between different bacteria. They provide a map to the answer.

The first question in this dichotomous key addresses Gram stain differences. metabolic characteristics. oxygen tolerance. bacterial morphology.

Plaques are associated with which of the following methods of laboratory identification of microorganisms? serological tests phage typing biochemical tests nucleic acid analysis

Staining is an important way to improve which of the following aspects of microscopy? resolution and contrast contrast and magnification numerical aperture and contrast magnification and resolution

What is an example of a negative stain? an endospore stain a capsule stain a flagella stain a Gram stain

Which of the following types of microscopes reveals the surface features of small molecules? a transmission electron microscope an atomic force microscope a confocal microscope a fluorescent microscope

Which of the following does NOT stain the bacterial cell? the Gram stain the acid-fast stain the endospore stain the negative stain

Which of the following CANNOT be used to definitively identify pathogenic bacteria? phage typing biochemical tests disease symptoms serological tests

A microbiologist is using heat to drive the stain carbolfuchsin into a smear. Which of the following staining procedures is being used? the Gram stain the endospore stain the acid-fast stain the capsule stain

If you needed to look at the fine details of the interior of a virus, which microscope would you use? scanning tunneling microscope fluorescent microscope bright-field microscope transmission electron microscope

Put the following steps of bacterial specimen preparation and staining in order: a. fixation b. application of staining dyes c. smear preparation a, c, b c, b, a b, c, a c, a, b

Which of the following groups of organisms belongs in the Domain Eukarya? bacteria archaea protozoa viruses

Which of the following is one-billionth of a meter? a centimeter a micrometer a millimeter a nanometer

Which of the following types of microscopes can magnify more than 2000X? a dark-field microscope a transmission electron microscope a phase-contrast microscope a bright-field microscope

Taxonomy consists of all of the following activities EXCEPT __________. staining classification nomenclature identification

The reagents crystal violet, iodine, and safranin are all associated with which of the following staining procedures? the flagella stain the acid-fast stain the endospore stain the Gram stain

Put the following taxonomic groups in order, from broadest group to most specific group: a. phylum b. genus c. family d. order a, d, c, b c, b, d, a a, c, d, b b, c, d, a

A scientist is using an objective lens with 40X magnification on his microscope. If the ocular lens magnifies 10X, what is the total magnification being used to visualize the specimen? 40X 50X 400X 4000X

If a microbiologist omitted the decolorizer from a Gram-stained smear, which of the following would happen? All cells in the smear would be pink. All cells in the smear would be colorless. Gram-positive cells would be pink and Gram-negative cells would be purple. All cells in the smear would be purple.

Which of the following is NOT equal to 50 millimeters? 5,000,000 nanometers 50,000 micrometers 5 centimeters 0.05 meters

What makes gram negative bacteria more infectious than gram positive bacteria? The outer layer contains lipopolysaccharide which is a immunogenetic, causing shock, fever, and blood clotting. Contains a thin layer of peptidoglycan Contains cholesterol in its cell wall Gram negative bacteria possess a greater number of flagella which can lead to more movement.

A scientific name contains information about its: family and species genus and species phylum and order class and family

A dichotomous key is used to: locate an organism identify an organism divide a kingdom interbreed species

The ability of a lens to gather light is referred to as its numerical aperture resolution refraction magnification contrast

Which of the following is(are) (a) magnifying lens(es)? condenser objective ocular dark-field stop both the objective and the ocular

Which of the following microscopes produces the highest resolution images? dark-field fluorescent differential interference atomic force scanning electron

A virologist wants to observe the surface features of virus particles she is studying. Which of the following microscopes would NOT be useful for her observations? atomic force scanning tunneling differential interference contrast transmission electron scanning tunneling

Which of the following phenomena produces magnification? the refraction of radiation as it passes through a lens the thickness of a microscopic specimen the wavelength of a radiation source the numerical aperture of a lens the length of an objective lens

Which of the following statements about transmission electron microscopy is FALSE? The sample is placed in a vacuum. Electrons are the source of illumination. Thin segments must be used. Glass lenses are used. Stains can be applied to improve contrast.

The dimensions of a virus are usually described in millimeters nanometers centimeters meters micrometers

Light rays that pass through the edge of a curved lens will be refracted more than those that pass through the center.

A virologist wants to observe the surface features of virus particles she is studying. Which of the following microscopes would NOT be useful for her observations? scanning tunneling scanning electron differential interference contrast atomic force transmission electron

A structure that appears in a transmission electron micrograph but is not actually present in the specimen is known as a(n) artifact. refraction. antigen. biofilm. mordant.

The Gram stain can be used to distinguish bacteria based on the structure of their cell walls.

The endospore stain reveals internal structures within cells of the genera Bacillus and Clostridium.

Acid-fast cells such as Mycobacterium lose the color of the primary stain in the presence of hydrochloric acid.

If a microbiology lab student left the safranin out of the Gram stain procedure, what would be the result? Gram-positive cells would be colorless and Gram-negative cells would be pink. Gram-positive cells would be pink and Gram-negative cells would be purple. Gram-positive cells would be purple and Gram-negative cells would be colorless. All cells would be pink. All cells would be purple.

All of the following are common to both the Gram stain and the acid-fast stain EXCEPT a decolorizing agent. a chemical mordant. a decolorizing agent and a counterstain. counterstain. primary stain.

Safranin dye is used as the counterstain in ________ stain(s). the acid-fast the flagellar the endospore the Gram both the Gram and the endospore

Heat is used to drive the stain into cells in the ________ staining procedure(s). endospore stain capsule stain Gram stain acid-fast stain both acid-fast and endospore stains

Carbolfuchsin is the ________ in the acid-fast stain. counterstain primary stain mordant decolorizer fixing reagent

Species and strains of microbes can be distinguished from one another phenotypically using electron microscopy. serological tests. Gram-stain reactions. G + C content. ribosomal RNA analysis

Acidic dyes are used for staining negatively charged molecular structures. work best in low pH environments. are negatively charged. are lipid soluble. are negatively charged and work best at low pH.

In Gram staining, ethanol-acetone is used as a primary stain. counterstain. mordant. decolorizing agent. drying agent.

Methylene blue can be used to stain DNA because it changes the pH and therefore the structure of DNA. forms ionic bonds with DNA. makes DNA electron dense. covalently bonds with DNA. is an effective fixing agent for nucleic acids.

The ________ stain makes use of malachite green. endospore flagellar electron microscopy acid-fast negative