Microbiology Evolving Science 3rd Edition by Slonczewski Foster Test Bank

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Microbiology Evolving Science 3rd Edition by Slonczewski Foster Test Bank

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Microbiology Evolving Science 3rd Edition by Slonczewski Foster Test Bank

CHAPTER 2: Observing the Microbial Cell

 

MULTIPLE CHOICE

 

  1. Who proved that stomach ulcers are caused by a bacterium?
a. Hooke d. Jenner
b. Marshall e. van Leeuwenhoek
c. Gram  

 

 

ANS:  B                    DIF:    Easy               REF:   Introduction   TOP:   VI

MSC:  Remembering

 

  1. The part of the human eye that is most involved in resolving an image is the:
a. iris d. retina
b. lens e. cornea
c. optic nerve  

 

 

ANS:  D                    DIF:    Medium         REF:   2.1                 TOP:   I.A

MSC:  Remembering

 

  1. A ball-shaped microbe is referred to as a:
a. bacillus d. strepto
b. coccus e. spirochete
c. vibrio  

 

 

ANS:  B                    DIF:    Easy               REF:   2.1                 TOP:   I.C.ii.b

MSC:  Remembering

 

  1. Resolution is the smallest distance by which two objects can be __________ and still be __________.
a. magnified; seen d. distinguished; separated
b. separated; distinguished e. magnified; distinguished
c. magnified; separated  

 

 

ANS:  B                    DIF:    Medium         REF:   2.1                 TOP:   I.A.i

MSC:  Understanding

 

  1. 400 nm is equivalent to:
a. 4.0 x 10-5 m d. 4.0 x 10-8 m
b. 4.0 x 10-6 m e. 4.0 x 10-9 m
c. 4.0 x 10-7 m  

 

 

ANS:  C                    DIF:    Medium         REF:   2.1                 TOP:   I.A

MSC:  Applying

 

  1. Which of these series arranges microbes from smallest to largest?
a. virus bacterium red blood cell paramecium
b. virus red blood cell bacterium paramecium
c. bacterium virus paramecium red blood cell
d. bacterium virus red blood cell paramecium
e. paramecium red blood cell bacterium virus

 

 

ANS:  A                    DIF:    Difficult         REF:   2.1                 TOP:   I.C

MSC:  Applying

 

  1. The heating of water when exposed to light is primarily due to:
a. reflection d. scattering
b. refraction e. fluorescence
c. absorption  

 

 

ANS:  C                    DIF:    Difficult         REF:   2.2                 TOP:   II.B.i.a

MSC:  Remembering

 

  1. Wavelength interference results in small observed objects (like bacteria) being surrounded by:
a. a capsule d. a dark field
b. a membrane e. a cell wall
c. an Airy disk  

 

 

ANS:  C                    DIF:    Medium         REF:   2.2                 TOP:   II.C

MSC:  Remembering

 

  1. What is the most important property that enables a lens to magnify an image?
a. absorption d. refraction
b. fluorescence e. scattering
c. reflection  

 

 

ANS:  D                    DIF:    Medium         REF:   2.2                 TOP:   II.C

MSC:  Understanding

 

  1. When two waves are out of phase by __________ wavelength, they produce destructive interference, canceling each others amplitude and resulting in contrast in the image.
a. one-tenth of a d. one-half of a
b. one-eighth of a e. one
c. one-quarter of a  

 

 

ANS:  D                    DIF:    Difficult         REF:   2.2                 TOP:   II.D

MSC:  Understanding

 

  1. Increasing the refractive index of the medium between the object and the objective lens increases:
a. refraction d. resolution
b. reflection e. wavelength
c. magnification  

 

 

ANS:  D                    DIF:    Difficult         REF:   2.2                 TOP:   II.D

MSC:  Understanding

 

  1. If a glass slide was submerged in a beaker of immersion oil, the slide would be:
a. undetectable d. fluorescent
b. brighter than its surroundings e. stained
c. darker than its surroundings  

 

 

ANS:  A                    DIF:    Medium         REF:   2.2                 TOP:   II.A.ii.a

MSC:  Applying

 

  1. What would happen if a lens had the same refractive index as air?
a. Light would not pass through the lens.
b. The image would be magnified more than with a glass lens.
c. The image would be magnified, but the resolution would be less than with a glass lens.
d. The image would be magnified, and the resolution would be greater than with a glass lens.
e. The image would not be magnified.

 

 

ANS:  E                    DIF:    Medium         REF:   2.2                 TOP:   II.C

MSC:  Applying

 

  1. The highest useful magnification for a light microscope is about:
a. 100X d. 100,000X
b. 1,000X e. 1,000,000X
c. 10,000X  

 

 

ANS:  C                    DIF:    Medium         REF:   2.2                 TOP:   II.D

MSC:  Applying

 

  1. A(n) __________ acts to vary the diameter of the light column in a light microscope.
a. condenser d. diaphragm
b. objective e. lens
c. ocular  

 

 

ANS:  D                    DIF:    Easy               REF:   2.3                 TOP:   III.B.i

MSC:  Remembering

 

  1. Which of these arranges the steps of the Gram stain into the correct order?
a. iodine crystal violet decolorizer safranin
b. safranin decolorizer crystal violet iodine
c. crystal violet decolorizer iodine safranin
d. crystal violet decolorizer safranin iodine
e. crystal violet iodine decolorizer safranin

 

 

ANS:  E                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Remembering

 

  1. When Gram stained, most eukaryotes appear:
a. colorless d. green
b. purple e. black
c. pink  

 

 

ANS:  C                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Remembering

 

  1. Malachite green is commonly used to stain:
a. eukaryotic cells d. bacterial endospores
b. Gram-negative cells e. acid-fast cells
c. Gram-positive cells  

 

 

ANS:  D                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.c

MSC:  Remembering

 

  1. As lens strength increases, the light cone __________ and the lens must be __________ the object.
a. narrows; nearer to d. widens; farther from
b. narrows; farther from e. widens; touching
c. widens; nearer to  

 

 

ANS:  C                    DIF:    Medium         REF:   2.3                 TOP:   III.A

MSC:  Understanding

 

  1. Staining helps to visualize bacteria by:
a. increasing the size of the cells d. increasing the magnification of the image
b. increasing the motility of the cells e. increasing the aberration of the image
c. increasing the contrast of the image  

 

 

ANS:  C                    DIF:    Medium         REF:   2.3                 TOP:   III.D.iii

MSC:  Understanding

 

  1. In a proper Gram stain, positive cells are stained by:
a. crystal violet only
b. safranin only
c. both crystal violet and safranin
d. neither crystal violet nor safranin
e. not enough information has been provided to know

 

 

ANS:  C                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Understanding

 

  1. Which two components of the Gram stain form a complex that is retained by Gram-positive cells?
a. crystal violet and iodine d. alcohol and safranin
b. safranin and iodine e. alcohol and iodine
c. crystal violet and safranin  

 

 

ANS:  A                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Understanding

 

  1. Which of the following is best visualized using a negative stain?
a. Gram-negative cell wall d. endospores
b. acid-fast cell wall e. flagella
c. capsule  

 

 

ANS:  C                    DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.d

MSC:  Understanding

 

  1. Which of these numeric aperture and light combinations would give the best resolution?
a. numeric aperture = 0.8, wavelength = 600 nm
b. numeric aperture = 0.8, wavelength = 500 nm
c. numeric aperture = 1.0, wavelength = 700 nm
d. numeric aperture = 1.0, wavelength = 600 nm
e. numeric aperture = 0.8, wavelength = 400 nm

 

 

ANS:  E                    DIF:    Difficult         REF:   2.3                 TOP:   III.A

MSC:  Applying

 

  1. What is the total magnification of a light microscope when using a 25X ocular and 40X objective lens?
a. 15X d. 1,000X
b. 65X e. 1,200X
c. 400X  

 

 

ANS:  D                    DIF:    Medium         REF:   2.3                 TOP:   III.B.i

MSC:  Applying

 

  1. What is the best explanation for a Gram-positive bacterium appearing pink after performing a Gram stain?
a. The crystal violet was left on for too long.
b. The iodine was left on for too long.
c. The decolorizer was left on for too long.
d. The safranin was left on for too long.
e. The stain was properly performed.

 

 

ANS:  C                    DIF:    Difficult         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Analyzing

 

  1. What is the best explanation for a Gram-negative bacterium appearing purple after performing a Gram stain?
a. The safranin was not applied.
b. The decolorizer was not applied.
c. The iodine was not applied.
d. The crystal violet was not applied.
e. The stain was properly performed.

 

 

ANS:  B                    DIF:    Difficult         REF:   2.3                 TOP:   III.E.ii.a

MSC:  Analyzing

 

  1. A useful application of dark-field optics is the study of bacterial:
a. motility d. shape
b. surfaces e. structure
c. interiors  

 

 

ANS:  A                    DIF:    Medium         REF:   2.4                 TOP:   IV.A

MSC:  Remembering

 

  1. Which of the following techniques are based upon wave interference?
a. X-ray diffraction and phase contrast microscopy
b. phase contrast and dark-field microscopy
c. bright-field and dark-field microscopy
d. X-ray diffraction and atomic force microscopy
e. scanning and transmission electron microscopy

 

 

ANS:  A                    DIF:    Medium         REF:   2.4                 TOP:   IV.A | IV.B

MSC:  Understanding

 

  1. In which type of microscopy do dust particles interfere the most?
a. bright-field microscopy d. interference microscopy
b. dark-field microscopy e. fluorescence microscopy
c. phase-contrast microscopy  

 

 

ANS:  B                    DIF:    Easy               REF:   2.4                 TOP:   IV.A.iii

MSC:  Understanding

 

  1. Which of the following would be best suited to observe the motility of microbial cells?
a. Gram stain d. negative stain
b. nuclear magnetic resonance e. phase-contrast microscopy
c. scanning electron microscopy  

 

 

ANS:  E                    DIF:    Medium         REF:   2.4                 TOP:   IV.B

MSC:  Understanding

 

  1. DAPI is a dye that is commonly used in _____________ microscopy.
a. bright-field d. confocal
b. dark-field e. fluorescence
c. phase contrast  

 

 

ANS:  E                    DIF:    Medium         REF:   2.5                 TOP:   V.B.i

MSC:  Remembering

 

  1. A fluorophore used in fluorescence microscopy that absorbs light at 260 nm would most likely fluoresce at:
a. 100 nm d. 400 nm
b. 200 nm e. 800 nm
c. 260 nm  

 

 

ANS:  D                    DIF:    Difficult         REF:   2.5                 TOP:   V.A

MSC:  Understanding

 

  1. The fluorophore DAPI specifically binds:
a. the cytoplasm d. RNA
b. the cell wall e. DNA
c. protein  

 

 

ANS:  E                    DIF:    Easy               REF:   2.5                 TOP:   V.B.i

MSC:  Understanding

 

  1. The aromatic groups of the fluorophore DAPI associate exclusively with the:
a. cell wall d. cell membrane
b. base pairs of DNA e. pili
c. flagella  

 

 

ANS:  B                    DIF:    Medium         REF:   2.5                 TOP:   V.B.i

MSC:  Understanding

 

  1. Fluorescence microscopy using labeled antibodies is referred to as:
a. immunofluorescence d. phase-contrast microscopy
b. autofluorescence e. dark-field microscopy
c. confocal microscopy  

 

 

ANS:  A                    DIF:    Easy               REF:   2.5                 TOP:   V.B.ii

MSC:  Understanding

 

  1. Which of the following can be used to localize proteins in a microbial cell?
a. DAPI and immunofluorescence
b. acridine orange and green fluorescent protein (GFP) fusions
c. DAPI and acridine orange
d. GFP fusions and immunofluorescence
e. DAPI and GFP fusions

 

 

ANS:  D                    DIF:    Difficult         REF:   2.5                 TOP:   V.B.ii | V.B.iii

MSC:  Understanding

 

  1. Which of these techniques can be used to localize the DNA sequence at the origin of replication in a bacterial cell?
a. fluorescence microscopy d. atomic force microscopy
b. phase contrast e. cryo-EM
c. X-ray diffraction  

 

 

ANS:  A                    DIF:    Difficult         REF:   2.5                 TOP:   V.B.iv

MSC:  Understanding

 

  1. Which form of microscopy is used with DNA microarrays to observe differences in gene expression?
a. light microscopy d. transmission electron microscopy
b. atomic force microscopy e. confocal fluorescence microscopy
c. scanning electron microscopy  

 

 

ANS:  E                    DIF:    Difficult         REF:   2.5                 TOP:   V.C

MSC:  Understanding

 

  1. The knife used to cut embedded specimens for observation by transmission electron microscopy is called a:
a. crystallographer d. polymer
b. microtome e. scalpel
c. grid  

 

 

ANS:  B                    DIF:    Easy               REF:   2.6                 TOP:   VI.B.i

MSC:  Remembering

 

  1. Atomic force microscopy measures __________ between a probe and an object to map the three-dimensional topography of a cell.
a. hydrogen bonds d. pH changes
b. covalent interactions e. magnetic interactions
c. van der Waals forces  

 

 

ANS:  C                    DIF:    Easy               REF:   2.6                 TOP:   VI.D.ii

MSC:  Remembering

 

  1. Which type of microscopy is particularly useful to study the surfaces of live bacteria?
a. atomic force d. dark-field
b. scanning electron e. bright-field
c. transmission electron  

 

 

ANS:  A                    DIF:    Easy               REF:   2.6                 TOP:   VI.D.ii

MSC:  Remembering

 

  1. Transmission electron microscopy commonly has a resolution of __________ times the highest resolution possible for light microscopy.
a. 10 d. 10,000
b. 100 e. 1,000,000
c. 1,000  

 

 

ANS:  C                    DIF:    Difficult         REF:   2.6                 TOP:   VI.A

MSC:  Understanding

 

  1. Which of the following would be most appropriate to visualize viral particles being assembled inside an infected bacterial cell?
a. dark-field microscopy d. scanning electron microscopy
b. atomic force microscopy e. transmission electron microscopy
c. fluorescence microscopy  

 

 

ANS:  E                    DIF:    Medium         REF:   2.6                 TOP:   VI.A | VI.B

MSC:  Understanding

 

  1. A microscopic structure that is interpreted incorrectly is a/an:
a. microtome d. antibody
b. crystal e. artifact
c. shadow  

 

 

ANS:  E                    DIF:    Easy               REF:   2.6                 TOP:   VI.C.i

MSC:  Understanding

 

  1. Unlike transmission electron microscopy, cryo-electron microscopy:
a. requires making thin slices of the sample to be viewed
b. does not require staining with heavy metals
c. may be used to view living tissues
d. uses a weaker electron beam
e. can provide a color image of the microbial cell

 

 

ANS:  B                    DIF:    Medium         REF:   2.6                 TOP:   VI.D

MSC:  Understanding

 

  1. The digitally combined images of cryo-EM can achieve resolution comparable to that of:
a. scanning electron microscopy d. X-ray crystallography
b. transmission electron microscopy e. dark-field microscopy
c. interference microscopy  

 

 

ANS:  D                    DIF:    Difficult         REF:   2.6                 TOP:   VI.D.i

MSC:  Understanding

 

  1. Which of the following techniques can visualize bacteria without focusing electromagnetic radiation?
a. cryo-electron microscopy d. atomic force microscopy
b. phase-contrast microscopy e. X-ray diffraction
c. dark-field microscopy  

 

 

ANS:  D                    DIF:    Medium         REF:   2.6                 TOP:   VI.D.ii

MSC:  Understanding

 

  1. The spots recorded on film during X-ray diffraction analyses are due to:
a. artifacts d. absorption
b. scattering e. fluorescence
c. wave interference  

 

 

ANS:  C                    DIF:    Medium         REF:   2.7                 TOP:   VII.A.i

MSC:  Understanding

 

  1. Which of these techniques would provide the best resolution of an enzymes structure?
a. scanning electron microscopy d. X-ray diffraction analysis
b. transmission electron microscopy e. atomic force microscopy
c. cryo-EM  

 

 

ANS:  D                    DIF:    Medium         REF:   2.7                 TOP:   VII.A.i

MSC:  Understanding

 

SHORT ANSWER

 

  1. List and describe three common shapes of bacteria.

 

ANS:

Bacilli (bacillus in the singular) are rod-shaped bacteria. Cocci (singular, coccus) are spherical-shaped bacteria. Spirochetes are tightly coiled spirals or corkscrew-shaped bacteria.

 

DIF:    Easy               REF:   2.1                 TOP:   I.C.ii               MSC:  Remembering

 

  1. Microbes were detected long before the invention of the microscope. How could this be?

 

ANS:

Detection is the ability to observe the presence of an object, such as when we detect a group of bacteria in a culture tube or growing on a surface like a food product. Even though we can detect the group, we cant resolve individual cells without the magnification afforded by microscopes.

 

DIF:    Easy               REF:   2.1                 TOP:   I.B.i                MSC:  Understanding

 

  1. Are all bacilli Bacillus? Explain.

 

ANS:

No. Bacillus refers to a particular genus of organisms that are commonly found in the soil. Although they are rod-shaped, the members of this genus are not the only bacteria that have this cellular morphology. The term bacillus refers to any rod-shaped microbe, which means that not all bacilli belong to the genus Bacillus.

 

DIF:    Easy               REF:   2.1                 TOP:   I.C.ii               MSC:  Understanding

 

  1. If your eyes had photoreceptors packed as closely as an eagles (about eight times greater than humans), would you be able to resolve a virus (100 nm in size) using a light microscope? Why or why not?

 

ANS:

No. Although your resolving power would be much improved, the light microscopes power will still be limited by the wavelengths of light that you can see (roughly 400 nm for human eyes). Objects less than 400 nm cannot be resolved by light in the visible spectrum.

 

DIF:    Medium         REF:   2.1                 TOP:   I.A                 MSC:  Applying

 

  1. Describe three conditions that are necessary for electromagnetic radiation to resolve an object.

 

ANS:

There must be contrast between the object and its surroundings. The wavelength of the radiation must be equal to or smaller than the size of the object. The detector must have sufficient resolution for the given wavelength.

 

DIF:    Medium         REF:   2.2                 TOP:   II.A.ii             MSC:  Remembering

 

  1. List and briefly describe four ways that light interacts with objects.

 

ANS:

(1) Absorption: light energy is absorbed by an object. (2) Reflection: a wavefront bounces off of an object at an angle equal to its incident angle. (3) Refraction: bending of light when it enters a substance that slows its speed. (4) A scattering wavefront interacts with an object of smaller dimensions than the wavelength.

 

DIF:    Medium         REF:   2.2                 TOP:   II.B.i              MSC:  Remembering

 

  1. Compare and contrast a simple stain (like methylene blue) with the Gram stain. What information about a microbial sample can be collected with each?

 

ANS:

Both staining procedures colorize bacterial cells, thereby increasing the samples contrast and improving resolution. A simple stain will color all microbial cells uniformly. This allows one to record the relative size, shape, and arrangement of any cells present. The Gram stain is a differential stain. In addition to size, shape, and arrangement, this procedure allows one to determine if the cells have a Gram-positive (purple) or Gram-negative (pink) cell wall structure.

 

DIF:    Medium         REF:   2.3                 TOP:   III.E.i             MSC:  Understanding

 

  1. List three different differential stains used in microbiology. What can be detected with each?

 

ANS:

The most common differential stain is the Gram stain. This procedure allows one to distinguish between cells having one membrane (Gram-positive) and two membranes (Gram-negative). Another common differential stain is the acid-fast stain. Carbolfuchsin stains the mycolic acidcontaining acid-fast cells of the genus Mycobacterium. The endospore stain is a differential stain that stains endospores with malachite green. Negative staining and antibody staining are also included in the text.

 

DIF:    Medium         REF:   2.3                 TOP:   III.E.ii            MSC:  Understanding

 

  1. What color are Gram-positive and Gram-negative cells when properly Gram stained? For each step of the Gram stain procedure, predict the colors of a Gram-positive or Gram-negative cell if that step were omitted during staining. Explain your reasoning.

 

ANS:

Properly Gram stained Gram-positive cells are purple and Gram-negative are pink.

(1) Skipping primary stain (crystal violet): Gram-positive and Gram-negative would both be pink. No crystal violetiodide complex would be formed in the Gram-positive wall. All cells would be decolorized and take on the color of safranin.

(2) Skipping mordant (iodine): Gram-positive and Gram-negative would both be pink. No crystal violetiodine complex would be formed in the Gram-positive wall. All cells would be decolorized and take on the color of safranin.

(3) Skipping decolorizer (alcohol): Gram-positive and Gram-negative would both be purple. The crystal violetiodine complex would remain in all cells. Although safranin still binds, the purple color is so much more intense that the pink of the safranin cannot be seen.

(4) Skipping secondary stain (safranin): Gram-positive cells would be purple. The Gram-negative cells would be colorless. The dye complex will be removed from the Gram-negative cells, but they will be difficult to see since the counterstain was not applied.

 

DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a          MSC:  Understanding

 

  1. Why do some bacteria appear purple after being Gram stained, while others appear pink?

 

ANS:

Gram-negative cells have a few layers of peptidoglycan cell wall and an outer lipopolysaccharide membrane. Gram-positive organisms have several layers of peptidoglycan and no outer membrane. The multiple layers of peptidoglycan retain the crystal violetiodine complex, so appear purple. Gram-negative cells do not retain the crystal violet because there are few layers of peptidoglycan and the outer membrane is disrupted by the decolorizer.

 

DIF:    Medium         REF:   2.3                 TOP:   III.E.ii.a          MSC:  Understanding

 

  1. Compare and contrast the radiation sources, lenses, and image-capturing devices used in light microscopy and transmission electron microscopy.

 

ANS:

The radiation source for light microscopy is a light, whereas for electron microscopy it is an electron source or tungsten filament. The lenses in the light microscope are glass, whereas magnets are used in electron microscopy. The lenses have similar functions and are arranged in the same order in both types of microscopy. Light microscopy uses a condenser lens, whereas the lens in electron microscopy is called the projection lens. The image-capturing device for light is the human eye, or sometimes a camera. The image-capturing device for electron microscopy is a fluorescent screen.

 

DIF:    Difficult         REF:   2.3 | 2.6         TOP:   III.B | VI.A     MSC:  Understanding

 

  1. Why are stains used in microscopy? Compare and contrast the stains used in light versus electron microscopy.

 

ANS:

Stains are used to increase the contrast between an object and its surroundings, so as to make it visible. The stains used in light microscopy are usually charged and interact with different cellular components. Positively charged dyes bind to negatively charged cell surfaces. They also are colored, so they impart color to a cell or its components. The stains used for electron microscopy are heavy metals or salts, which increase the density of certain components, again increasing contrast. In electron microscopy, the image of the microbe is always black and white.

 

DIF:    Difficult         REF:   2.3 | 2.6         TOP:   III.D | VI.B     MSC:  Understanding

 

  1. Name two types of microscopy that are suitable for directly studying bacterial motility. What interaction of light with the microbe is most important for each of these techniques?

 

ANS:

Either dark-field or phase-contrast microscopy could be used. In dark-field microscopy, the condenser contains an opaque disk held by three spider legs across an open ring. No light travels directly up through the specimen, so the only light that reaches the eye is light that is scattered by objects on the slide. This scattered light allows detection of objects that are too small to be resolved by light rays. Phase-contrast microscopy exploits differences in refractive index between cell components and transforms them into differences in intensity of transmitted light due to wave interference.

 

DIF:    Medium         REF:   2.4                 TOP:   IV.A | IV.B    MSC:  Understanding

 

  1. If you are interested in studying the localization of a protein in a bacterial cell, what techniques would provide you with the best information?

 

ANS:

Fluorescence microscopy can be used to study protein localization. One method would be to use fluorescently tagged antibodies to detect the proteins using immunofluorescence microscopy. Another possibility would be to make green fluorescent protein fusions with the protein of interest. These hybrid proteins would fluoresce wherever they are in the cell.

 

DIF:    Difficult         REF:   2.5                 TOP:   V.B                MSC:  Understanding

 

  1. Define a fluorophore and give three examples of how it can be used to label cells.

 

ANS:

A fluorophore is a fluorescent molecule that can be used to stain a specimen for observation with a fluorescence microscope. Some fluorophores, such as DAPI, have affinity for certain cell chemicals. Antibodies can be labeled with fluorescent dyes and reacted with specific targets in immunofluorescence. Short sequences of DNA attached to a fluorophore can be used to hybridize and label target DNA.

 

DIF:    Difficult         REF:   2.5                 TOP:   V.B                MSC:  Understanding

 

  1. Archaea and Bacteria differ in the genetic sequences of their ribosomal RNA genes. How can this difference be used to microscopically differentiate between members of these domains?

 

ANS:

Short DNA sequences that are homologous to either the Bacterial or Archaeal sequences can be conjugated to fluorophores that emit different wavelength light. These probes will anneal to the complementary DNA in the corresponding cells in a sample. When viewed using a fluorescence microscope, the archaeal and bacterial cells will have different colors. This is referred to as fluorescence in situ hybridization, or FISH, analysis.

 

DIF:    Difficult         REF:   2.5                 TOP:   V.B.iv            MSC:  Applying

 

  1. Most electron micrographs in microbiology textbooks are in color. Is this normal for an electron micrograph? Why or why not?

 

ANS:

Electron micrographs are not naturally colored. The original image is produced when the electrons bombard a fluorescent screen. The resultant image is processed by a computer to appear as black and white with intensities in the entire range of grays in between. These images are later colorized using computer software (like Photoshop) to improve the aesthetics and provide additional information.

 

DIF:    Difficult         REF:   2.6                 TOP:   VI.A            &

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