Chapter 2 Quiz Observing The Microbial Cell

b Higher resolution allows the detection of smaller objects.

Eagles can see smaller objects than humans can because Select one: a. eagle eyes have lower resolution. b. eagle eyes have higher resolution. c. eagles have compound eyes. d. eagle photoreceptor cells are not as tightly packed in their retina as human photoreceptor cells.

a The nosepiece contains one or more objective lenses of various magnifications.

The nosepiece of a compound microscope contains Select one: a. objective lenses. b. ocular lenses. c. condenser lenses. d. the diaphragm.

a 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.

To clearly observe a single bacterium's subcellular structure, the best tool is Select one: a. a transmission electron microscope. b. the unaided human eye. c. X-ray crystallography. d. a light microscope.

c 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.

Which of the following is an advantage of electron microscopy? Select one: a. Living specimens can be observed. b. The microscope is inexpensive and easy to use. c. Specimens can be observed at high resolution. d. Motile specimens can be observed.

b In dark-field microscopy the microbes are seen as bright objects. Any material, such as dust particles, will scatter light and appear as bright specks. This will obscure the image of the specimen.

A disadvantage of dark-field microscopy is that Select one: a. the microbes are seen as dark objects. b. any objects in the specimen will scatter light, leading to increased background noise. c. the microbes to be observed must be killed, fixed, and stained. d. it only reveals the same structures as bright-field microscopy.

c

A nanometer, nm, is equal to Select one: a. 10-2 meters. b. 10-6 meters. c. 10-9 meters. d. 10-12 meters.

a

A physician informs you that the pathogen that has been causing your infection is a bacillus. When you look at a magnified image of cells from the infection you see cells of many different shapes and sizes. What shape is the pathogen? Select one: a. a rod b. a sphere c. a spiral d. There is no way to determine the shape.

b The resolution of the human retina is about 150 μm. Hence, a 100-fold magnification is the minimum required. For more information, see Section 2.1.

A specimen has a diameter of 1.5 μm. What is the minimum magnification that will allow a human to resolve this object? Select one: a. 10x b. 100x c. 1,000x d. 10,000x

d Small particles, like bacteria, scatter light and cause suspensions with more than about 1 million cells per ml to look cloudy.

Bacterial cultures appear cloudy because of the _______________ of light. Select one: a. refraction b. reflection c. absorption d. scattering

d In dark-field microscopy, the scattering of light allows objects smaller than the wavelength of light to be viewed as bright images on a dark field.

Dark-field microscopy depends on which characteristic of light? Select one: a. Fluorescence b. Absorption c. Reflection d. Scattering

b The use of immersion oil increases the amount of light collected by the objective lens. This increases the numeric aperture of the system and improves resolution.

Distortion at the highest levels of magnification is decreased by Select one: a. using a lens with a smaller numerical aperture. b. the use of immersion oil. c. using a longer wavelength of light. d. using a lower-power objective lens.

b Empty magnification refers to an increase in an image size with no increase in resolution.

Empty magnification occurs when Select one: a. a microscope without lenses is used. b. the size of an image increases with no increase in resolution. c. the size of an image increases with an increase in resolution. d. the resolution of an image increases while the size of the image decreases.

c For a molecule to fluoresce (emit light), it must first have an electron boosted to a higher energy level by absorption of a photon.

For a molecule to fluoresce, it must first Select one: a. reflect light. b. transmit light. c. absorb light. d. scatter light.

a The emitted light is always of a longer wavelength (lower energy) than the absorbed light (excitation wavelength). Of the colors listed, only blue has a shorter wavelength than green.

Green fluorescent protein can be fused to other proteins to visualize them via fluorescence microscopy. If the emitted light is green, what color light may have been used as the excitation wavelength? Select one: a. Blue b. Orange c. Red d. Yellow

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

In a proper Gram stain, Gram-positive cells appear _______________ in color. Select one: a. red b. blue c. green d. purple

a 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.

In bright-field microscopy Select one: a. the specimen absorbs light and appears dark. b. the specimen reflects light and appears light. c. there is no contrast between the specimen and the medium. d. any subcellular structure may be observed.

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

In microscopy, the term "resolution" refers to Select one: a. the smallest distance by which two objects can be separated and still be distinguished. b. the ability to identify which microbial species is being viewed under the microscope. c. the ability to detect any microbial life forms. d. when a motile protist swims out of the field of view.

b Objects can only be resolved by wavelengths of light smaller than the size of the object to be resolved.

In order to resolve spherical bacteria 1 ìm in diameter, Select one: a. any wavelength of light may be used. b. light of a wavelength less than 1 ìm must be used. c. light of a wavelength greater than 1 ìm must be used. d. the bacteria must be coated with gold particles.

c Although microscopes are needed to resolve bacterial cells, they can be detected without the aid of a microscope if their density is high enough.

Microbial cells can be detected by the human eye Select one: a. only when magnified at least 400 times. b. only when they are resolved as individual cells. c. when a large population is present. d. only when a microscope is available.

a 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.

The best microscope technique for observing the arrangement of different proteins of the surface of bacteria is Select one: a. scanning electron microscopy. b. transmission electron microscopy. c. phase-contrast microscopy. d. X-ray crystallography.

a Magnification requires refraction, the bending of light as it passes through an object.

The characteristic of light that allows magnification by a microscope is Select one: a. refraction. b. reflection. c. absorption. d. scattering.

c The modern electron microscope was developed in the 1950s

The electron microscope began being used in biology in the Select one: a. 1750s. b. 1850s. c. 1950s. d. 2000s.

a A "parabolic surface" is called such because it is in the shape of a parabola. When light passes through a parabola, the refraction spreads light waves and magnifies an image.

The lens shape that spreads light waves to magnify an object is a Select one: a. parabola. b. square. c. circle. d. triangle.

d 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.

The path of light through a compound microscope is as follows: Select one: a. Objective lens, specimen, condenser lens, ocular lens b. Specimen, condenser lens, objective lens, ocular lens c. Specimen, objective lens, ocular lens, condenser lens d. Condenser lens, specimen, objective lens, ocular lens

b The resolution of the human eye is about 150 μm because that is how closely our photoreceptor cells are spaced.

The resolution of the human retina is Select one: a. 150 nm. b. 150 μm. c. 150 mm. d. 150 cm.

d 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.

The three-dimensional structure of a virus particle would best be visualized using Select one: a. bright-field microscopy. b. confocal laser scanning microscopy. c. phase-contrast microscopy. d. cryo-electron tomography.

c Prokaryotic cells tend to be smaller than eukaryotic cells.

The typical prokaryotic cell is Select one: a. much larger than the typical eukaryotic cell. b. about the same size as the typical eukaryotic cell. c. much smaller than the typical eukaryotic cell. d. more easily resolved under a microscope than a eukaryotic cell.

d 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).

Viruses cannot be observed using a light microscope because viruses Select one: a. do not absorb or scatter light. b. are not stained by simple stains. c. are only found inside host cells. d. are too small to resolve using visible light.

c 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.

Visualization techniques that rely on interference effects are Select one: a. bright-field and dark-field microscopy. b. phase-contrast microscopy and dark-field microscopy. c. phase-contrast microscopy and X-ray crystallography. d. X-ray crystallography and scanning electron microscopy.

b The higher the magnification, the smaller the field of view; thus, there is a trade-off between magnification and field of view—the larger the objects appear in the ocular lens, the less of the total specimen will be visible at any one time. Highly motile cells can, therefore, rapidly swim out of the field of view at higher magnifications.

What is the relationship between magnification and field of view? Select one: a. There is a positive relationship such that as the magnification increases, the field of view increases. b. There is an inverse relationship such that as the magnification increases, the field of view decreases. c. There is no relationship between the two; they vary independently. d. There is a fixed relationship, but it depends on the type of microscopy used.

d The total magnification is the product of the ocular lens and the objective lens (20x • 45x). It does not matter that the microscope is binocular—each eye will have the same total magnification.

What is the total magnification of a binocular microscope when the ocular lenses have a magnification of 20x and a 45x objective lens is used? Select one: a. 65x b. 85x c. 450x d. 900x

d Scattering occurs when light interacts with an object of smaller dimensions than the wavelength of the light.

Which of the following occurs when a wave front interacts with an object of smaller dimension than the wavelength? Select one: a. Absorption b. Reflection c. Refraction d. Scattering

a Atomic force microscopy is a type of scanning probe microscopy (SPM). SPM methods differ from light and electron microscopy, in which the sample interacts with a beam of light or electrons. Instead, SPM methods measure a physical interaction, such as the "atomic force" between the sample and a sharp tip.

Which technique does NOT rely on a beam of electrons or light interacting with the specimen? Select one: a. Atomic force microscopy b. Bright-field microscopy c. Cryo-electron tomography d. Interference microscopy

d X-ray diffraction analysis, also known as X-ray crystallography, uses X-ray diffraction (interference patterns) from crystallized macromolecules to determine structure at atomic resolution.

Which technique requires prior crystallization of the specimen? Select one: a. Atomic force microscopy b. Cryo-electron tomography c. Dark-field microscopy d. X-ray diffraction analysis