Mastering Microbiology: Chapter 3.
Why do electron microscopes have higher resolving power than light microscopes? The copper grid used in electron microscopy provides enhanced resolution. Electrons have a smaller wavelength than visible light, leading to higher 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.
What is the role of lenses in microscopy? Lenses increase the contrast to determine structural differences in stained specimens. Lenses focus either light or electrons to create a magnified image of a specimen. 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.
Acid-fast staining is used to detect members of which bacterial genus? Staphylococcus Streptococcus Mycobacterium Clostridium
Mycobacterium
Which of the following is a lens found on electron microscopes but not on light microscopes? Objective lens Condenser lens Projector lens Eyepiece lens
Projector lens
In a typical brightfield microscope (seen in the animation), at which point does magnification begin? The ocular lens The condenser lens The lamp The stage The objective lens
The objective lens
What is the fate of the electrons that interact with a specimen in an electron microscope? They may be absorbed, reflected, or refracted by the specimen. They are reflected by the specimen. They are absorbed by the specimen. They are refracted by the specimen.
They may be absorbed, reflected, or refracted by the specimen.
What is the role of the ocular lens? To recreate the image in the viewer's eye To adjust the wavelength of light To do the bulk of the magnification To focus the light to a high intensity in a small area
To recreate the image in the viewer's eye
In a completed Gram stain, gram-negative bacteria are colorless. True False
false
Which type of stain is most useful in helping clinicians to decide which antibiotic to prescribe for a bacterial infection? Gram stain simple stain negative stain endospore stain flagella stain
gram stain
You are studying a cell structure that is approximately 100 nm in size. Which of the following provides the greatest magnification you can use to see the cellular structure in three-dimensions? -darkfield microscope -phase-contrast microscope -scanning electron microscope -brightfield microscope -transmission electron microscope
scanning electron microscope
Which two staining techniques employ a mordant? Gram stain; Acid-fast stain. Simple stain; Acid-fast stain. Capsule stain; Flagella stain. Gram stain; Capsule stain. Gram stain; Flagella stain.
Gram stain; Flagella stain.
What is meant by light rays being divergent? It is spreading out It is coming together to a focused beam It is heading upwards
It is spreading out
A virus measures 100 nm in length. What is its length in μm? a. 0.001 μm b. 1 μm c. 10 μm d. 0.01 μm e. 0.1 μm
-0.1 μm
Which waxy molecule, found in the cell wall of acid-fast bacteria, prevents these cells from being Gram stained? Carbolfuchsin Acid-alcohol Methylene blue Mycolic acid
Mycolic acid
Which of the following staining procedures is matched with the principal use for that stain? flagella stain used to distinguish dormant structures formed during adverse environmental conditions negative stain used to differentiate cell wall components acid-fast stain for microbes with waxy cell walls endospore stain to visualize structures which enable bacteria to move and swim
acid-fast stain for microbes with waxy cell walls
Bacterial smears are fixed before staining to make the cells visible. make their walls permeable. affix the cells to the slide. accept stain.
affix the cells to the slide.
Part B - Relative Sizes of Microorganisms To select the appropriate microscope, you need to understand the relative sizes of eukaryotic cells, prokaryotic cells, intracellular structures, and viruses. This activity asks you to rank items from smallest to largest. Drag the appropriate image to each box, arranging the items in size from smallest to largest.
bacterial plasmids 20 nm mastadenovirus 30 nm gram positive bacteria6 micrometers giardia lamblia (protozoa) 7 micrometers Clonorchis sineensis (trematode) 5 mm
The purpose of a mordant in the Gram stain is to remove the simple stain. make gram-negative cells visible. prevent the crystal violet from leaving the cells. make the flagella visible. make the bacterial cells larger.
prevent the crystal violet from leaving the cells
Which microscope is best used for observing the surfaces of intact cells and viruses? -phase-contrast microscope -darkfield microscope -brightfield microscope -scanning electron microscope -fluorescence microscope
scanning electron microscope
Which microscope is used to see intracellular detail in a living cell? -brightfield microscope -fluorescence microscope -two-photon microscope -transmission electron microscope -atomic force microscope
two-photon microscope
Which microscope uses visible light? -differential interference contrast microscope -scanning acoustic microscope -fluorescence microscope -confocal microscope -scanning electron microscope
-differential interference contrast microscope
In using this microscope, the observer does NOT look directly at an image through a lens. -phase-contrast microscope -compound light microscope -darkfield microscope -electron microscope -fluorescence microscope
-electron microscope
Which microscope achieves the highest magnification and greatest resolution? -phase-contrast microscope -compound light microscope -electron microscope -darkfield microscope -fluorescence microscope
-electron microscope
Which demonstrates better resolution? -measuring two yeast cells as individually having a diameter of 10μm -observing two adjacent bacteria as individually having a width of 0.3μm -measuring two bacteria arranged end to end as individually having a length of 2μm -observing a clump of algae 0.5mm by 0.75 mm -measuring a flea as 1.2mm at the longest point
-observing two adjacent bacteria as individually having a width of 0.3μm
Which microscope is most useful for visualizing a biofilm? -phase-contrast microscope -transmission electron microscope -compound light microscope -fluorescence microscope -scanning acoustic microscope
-scanning acoustic microscope
A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)? 1.5 mm 0.15 mm 0.015 mm 1500 mm 15 mm
0.15 mm
Part F- describing functions of parts of the microscope In addition to knowing the names of the parts of the compound light microscope, you also need to know the functions of these parts. This activity asks you to match the appropriate function with each part of the microscope. Match each microscope part with its function.
1. Fine focus knob:used after initial focusing to sharpen the image 2. Ocular lens:lens that you look through 3. Objective lens:lens that is closest to the slide and provides initial magnification of a specimen 4. Coarse focus knob:used for initial focusing; should never be used when the high-power objective lens or oil immersion objective lens is in place 5. Stage:platform on which the slide is placed for viewing 6. Condenser lens:used to focus the light from the illuminator onto the slide 7. Diaphragm:controls how much light from the illuminator reaches the specimen
Which of the following places the steps of the Gram stain in the correct order? 1-Alcohol-acetone 2-Crystal violet 3-Safranin 4-Iodine 1-2-3-4 4-3-2-1 2-1-4-3 1-3-2-4 2-4-1-3
2-4-1-3
Part C - Metric measurements and conversions (micrometers and nano-meters) Chlamydia trachomatis elementary bodies measure approximately 0.25 micrometers in diameter. What is this measurement expressed in nano-meters (nm)? 2.5nm 25nm 2500 nm 250 nm 25,000 nm
250 nm
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
A transmission electron microscope
Which of the following pairs of terms is properly matched? Methylene blue—decolorizing agent Acid-alcohol—decolorizing agent Steam heat—decolorizing agent Carbolfuchsin—decolorizing agent
Acid-alcohol—decolorizing agent
Which of the following is NOT true regarding the acid-fast stain? It is used to identify members of the genus Mycobacterium. Acid-fast cells retain the primary dye after treatment with acid-alcohol. Non-acid-fast microbes appear blue in a completed acid-fast stain. If cells are acid-fast, they are gram-negative. Acid-fast cells appear red in a completed acid-fast stain.
C) If cells are acid-fast, they are gram-negative.
Why is a specimen smaller than 200 nm not visible with a light microscope? The lenses only go to 100 X magnification power. Anything smaller than 200 nm cannot interact with visible light. It is too easy to lose on the stage. Visible light is only good at wavelengths below 390 nm.
Anything smaller than 200 nm cannot interact with visible light.
What happens to the light rays when they hit the specimen? They are reflected, refracted, or absorbed by the specimen. They are absorbed by the stage. They are diverted to the ocular lens. They are focused into a small area towards the objective lens.
They are reflected, refracted, or absorbed by the specimen.
Which of the following is a characteristic shared by both electron and light microscopes? They both utilize white light to magnify the specimen. Both microscopes have a resolving power of 0.01 nm. They both employ the use of objective lenses. Both microscopes require an internal camera to visualize the specimen.
They both employ the use of objective lenses.
Assume you stain Bacillus by applying malachite green with heat and then counterstaining with safranin. Through the microscope, the green structures are endospores. capsules. flagella. cell walls. The answer cannot be determined.
endospores
Which of the following pairs is mismatched? -confocal microscope - produces a three-dimensional image -scanning tunneling microscope - allows visualization of atoms -scanning electron microscope - produces a three-dimensional image -darkfield microscope - uses visible light -fluorescence microscope - uses a fluorescent light
fluorescence microscope - uses a fluorescent light
Most microorganisms are too small to be viewed with the unaided eye. Different types of microscopes have been developed that allow us to visualize these small organisms. The most appropriate microscope for viewing a particular organism or structure depends on the size of the organism and the particular information about it that you are looking for. For viewing eukaryotic cells and bacteria, light microscopes are generally used; several different types of light microscopes are available. To view viruses and the internal structure of bacterial cells, as well as fine structural details of eukaryotic cells, scanning electron microscopes and transmission electron microscopes are generally preferred because they provide greater magnification and resolution. However, preparing specimens to be viewed with these microscopes requires a greater investment in time and technique. Scanning electron microscopes are especially suited to viewing the surface of a microorganism and to obtaining a three-dimensional perspective of the organism's overall shape. Transmission electron microscopy is useful for viewing fine structural details in cross sections of microorganisms. Which type of microscopy you choose depends primarily on the size of the object; other considerations include how much time and effort are needed to prepare the specimen for microscopy, whether you will be viewing living or fixed cells, and whether you want a cross-sectional or surface view. Also, to be able to express the size of microorganisms and viruses, you will need an understanding of the following metric units: millimeters, micrometers, nanometers, and picometers. Read through Foundation Figure 3.2, and then complete the activity and questions below.
for questions below
part a Selecting the Most Appropriate Method of Viewing This activity asks you to sort items according to the most appropriate method for viewing. For each of the following items, indicate which viewing method is most appropriate-the unaided eye, light microscopy, scanning electron microscopy, or transmission electron microscopy-by dragging it into the correct bin.
unaided eye examining your cat for the presence of fleas light microscope examining a clinical specimen, such as a sputum smear, for the presence of bacteria examining a blood smear for the presence of malarial parasites scanning electron microscope viewing the three-dimensional shape of a protozoan and the arrangement and distribution of cilia on its surface determining the three-dimensional shape and arrangement of bacterial cells transmission electron microscope confirming the 9 + 2 microtubule arrangement in a eukaryotic flagellum viewing ribosomes (20 nm) within a bacterial cell viewing a cross section of poliovirus (30 nm) viewing the layers of the gram-negative cell wall in cross section
Which of the following signs and symptoms is NOT associated with active pulmonary tuberculosis? Cough with blood Fever Weight gain Chest pain
weight gain
