Microbiology: MCB 3020 Smart Connect Ch 2 HW Flashcards


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Microbiology
Chapter 2
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1

In microscopy, the term “resolution” refers to
Choose one:

A. when a motile protist swims out of the field of view.

B. the ability to identify which microbial species is being viewed under the microscope.

C. the smallest distance by which two objects can be separated and still be distinguished.

D. the ability to detect any microbial life forms.

C. the smallest distance by which two objects can be separated and still be distinguished.

Resolution is the smallest distance by which two objects can be separated and still be distinguished.

2

A nanometer, nm, is equal to _____ meters.
Choose one:

A. 10–12

B. 10–2

C. 10–6

D. 10–9

D. 10–9

A nanometer is equal to 10–9 meters.

3

Which of the following bacterial shapes is believed to have evolved only once?
Choose one:

A. Coccus

B. Bacillus

C. Spirochete

D. Diplococcus

C. Spirochete

Cocci (in any arrangement) and bacilli are common to both bacteria and archaea. Spirochetes are found in only one taxon of bacteria.

4

To clearly observe a single bacterium’s subcellular structure, the best tool is
Choose one:

A. X-ray crystallography.

B. a light microscope.

C. a transmission electron microscope.

D. the unaided human eye.

C. a transmission electron microscope.

Bacteria are too small for their subcellular structure to be seen clearly with the unaided human eye or even a light microscope. X-ray crystallography is best for deciphering the structure of proteins. Transmission electron microscopy is the best tool listed for resolving subcellular bacterial structure.

5

A physician informs a patient that the pathogen that has been causing their infection is a bacillus. When they look at a magnified image of cells from the infection, they see cells of many different shapes and sizes. What shape is the pathogen?
Choose one:

A. a rod

B. a sphere

C. There is no way to determine the shape.

D. a spiral

A. a rod

A bacillus is a rod-shaped bacterium.

6

Viruses cannot be observed using a light microscope because viruses
Choose one:

A. are not stained by simple stains.

B. are only found inside host cells.

C. do not absorb or scatter light.

D. are too small to resolve using visible light.

D. are too small to resolve using visible light.

Most viruses are smaller than 200 nm and are, therefore, unable to be resolved by light with wavelengths in the visible range (400–750 nm).

7

In a proper Gram stain, Gram-positive cells appear _______________ in color.
Choose one:

A. blue

B. green

C. purple

D. red

C. purple

The primary stain in the Gram stain, crystal violet, is retained by Gram-positive cells.

8

The path of light through a compound microscope is
Choose one:

A. specimen, condenser lens, objective lens, ocular lens.

B. specimen, objective lens, ocular lens, condenser lens.

C. condenser lens, specimen, objective lens, ocular lens.

D. objective lens, specimen, condenser lens, ocular lens.

C. condenser lens, specimen, objective lens, ocular lens.

The condenser consists of one or more lenses that collect a beam of rays from the light source onto a small area of the slide containing the specimen. The objective and ocular lenses collect light that has passed through the specimen.

9

In bright-field microscopy
Choose one:

A. the specimen reflects light and appears light.

B. there is no contrast between the specimen and the medium.

C. any subcellular structure may be observed.

D. the specimen absorbs light and appears dark.

D. the specimen absorbs light and appears dark.

In bright-field microscopy, an object such as a bacterial cell is perceived as a dark silhouette blocking the passage of light. Details of the dark object are defined by the points of light surrounding its edge.

10

Wet mount preparation of specimens
Choose one:

A. allows for viewing specimens in as close to the natural state as possible.

B. maximizes contrast between specimen and background.

C. has the best resolution.

D. prevents overheating.

A. allows for viewing specimens in as close to the natural state as possible.

Wet mounts allow for viewing cells that are still alive and in a “natural” state, but have low contrast as most cells are transparent and therefore have limited resolution. Water also absorbs light and converts it to heat.

11

Fixation and stained preparation of specimens
Choose one:

A. is the simplest method of preparation.

B. allows viewing of live cells.

C. causes cells to stay in one place and improves contrast as well as usually imparts color, improving detection.

D. allows for easier viewing of swimming specimens.

C. causes cells to stay in one place and improves contrast as well as usually imparts color, improving detection.

Fixing and staining will kill a specimen but improves contrast and resolution.

12

Simple stains
Choose one:

A. add dark color to all cells specifically, improving contrast.

B. detect mycolic acids.

C. detect spores in endospore-producing species.

D. allow for differentiating among cell wall types.

A. add dark color to all cells specifically, improving contrast.

Simple stains affect all cells the same, and increase contrast. Spore staining will affect the endospore coat only. Acid-fast staining affects mycolic acids. Gram-staining differentiates the types of cell wall.

13

Crystal violet
Choose one:

A. complexes with iodide ions, producing a positively charged molecule that stays more strongly within the peptidoglycan cell wall.

B. cannot stay near to the outer membrane under normal circumstances.

C. stains cell walls irreversibly.

D. can penetrate only the top layers of peptidoglycan.

A. complexes with iodide ions, producing a positively charged molecule that stays more strongly within the peptidoglycan cell wall.

The Gram stain procedure begins with crystal violet, which can stain any cell and penetrates the cell wall readily if it is exposed. It can be fixed within the layers of peptidoglycan using iodine, which will complex as an ion with the dye. When decolorizer is used, it removes only loosely bound crystal violet, which would include any on the outer membrane.

14

Which of the following is an advantage of electron microscopy?
Choose one:

A. Motile specimens can be observed.

B. Specimens can be observed at high resolution.

C. Living specimens can be observed.

D. The microscope is inexpensive and easy to use.

B. Specimens can be observed at high resolution.

Electron microscopy affords high resolution because the wavelength of electrons is small. However, the electron microscope is an expensive, sophisticated piece of equipment. Samples are nonliving and artifacts may arise because samples must be stained with an electron-dense material and sectioned.

15

Visualization techniques that rely on interference effects are
Choose one:

A. phase-contrast microscopy and X-ray crystallography.

B. X-ray crystallography and scanning electron microscopy.

C. bright-field and dark-field microscopy.

D. phase-contrast microscopy and dark-field microscopy.

A. phase-contrast microscopy and X-ray crystallography.

Both phase-contrast microscopy and X-ray crystallography produce images based on interference patterns generated by light interacting with the specimen. Bright-field microscopy relies on light absorption and dark-field microscopy relies on light scattered by the specimen. Scanning electron microscopy relies on electrons reflecting from the specimen.

16

The best microscope technique for observing the arrangement of different proteins of the surface of bacteria is
Choose one:

A. X-ray crystallography.

B. scanning electron microscopy.

C. transmission electron microscopy.

D. phase-contrast microscopy.

B. scanning electron microscopy.

In scanning electron microscopy, electrons reflect off a specimen to reveal the contours of its three-dimensional surface. Transmission electron microscopy is best for observing the inside of a bacterium, not the surface. Phase-contrast microscopy, a form of light microscopy, does not have enough magnifying power to observe proteins, and X-ray crystallography is best for observing crystals of pure protein, not a mixture of proteins on a cell surface.

17

The three-dimensional structure of a virus particle would best be visualized using __________ microscopy.
Choose one:

A. confocal laser scanning

B. cryo-electron

C. phase-contrast

D. bright-field

B. cryo-electron

By combining multiple images taken from different angles using a high-power electron beam, a three-dimensional image can be generated for symmetrical objects like virus particles.