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A compound microscope uses two lenses at once to magnify the image of a specimen. The _____ lens is found in the eyepiece and the _____ lens is found in the revolving nosepiece.
Which component of the microscope is found directly under the stage, and contains two sets of lenses that collect and concentrate light as it passes upward from the light source into the lens systems?
Which property of the lens describes its ability to show two adjacent objects as discrete entities?
expressed mathematically as a function of the wavelength of light and the numerical aperture
platform with an opening in the center that allows for the passage of light through the specimen
degree of enlargement of the specimen when using a specific lens or combination of lenses
Loss of bent, or refracted, light results in a reduced numerical aperture, which diminishes the resolving power of the objective lens. Adding which of the following substances between the slide and the lens acts to decrease the refraction of light?
Which of the following objective lenses is the ONLY lens that should be used with oil immersion?
High-power lens (100X)
The use of clean lenses increases the efficiency of the microscope. While dry lenses should be cleaned with _____, the oil-immersion lens can be cleaned with _____, followed by 95% ethanol.
lens paper; xylol
Which of the following microscope parts should routinely be adjusted to control the light source and provide optimal illumination of the specimen?
With respect to the image of a microscope specimen, refraction of light by the objective lens enhances __________.
refers to the apparent size of the specimen when viewed through the microscope. Light bends at the convex surfaces of the objective lens, causing light rays to diverge and radiate outward. This divergence of light creates an image of the specimen that is larger than what would normally be seen by the naked eye.
In a compound light microscope, what is the function of the condenser?
To concentrate light on the specimen. Light diverges through the air as it exits the light source. The condenser gathers this divergent light and concentrates it on the specimen.
Which of the following is the most appropriate way to carry a microscope?
The student correctly grasps the microscope arm with one hand and supports the base with the other hand. This minimizes the risk of dropping the heavy microscope during transport.
You have just rotated the 40X objective into position after viewing the specimen with the 10X objective. What would your next step most likely be?
Adjust the fine focus knob. After changing objectives, check to make sure your image is well focused . Your objectives are most likely parfocal. The working distance between the 40X objective and the specimen is very small, so adjusting the fine focus will help avoid smashing the objective into the slide.
When you look through the ocular lenses, you see this image of the endospore-forming bacteria Bacillus anthracis under oil. Which of the following qualities is most lacking in this image?
Contrast, which is lacking in this image, refers to the difference in light intensity between the specimen's features and between the specimen and the background. You can enhance contrast by adjusting the lamp intensity dial and the aperture diaphragm on the condenser.
While looking through a microscope at 400X total magnification, you see this image. To improve the quality of this image, what should you do?
The specimen is in focus, but contrast is poor. You can enhance contrast by moving the aperture diaphragm toward the closed position. This restricts the angles at which light strikes the specimen and thereby tends to eliminate the bright, washed-out appearance of the image. This is a better alternative than reducing lamp intensity. Reducing the lamp intensity would make the image less bright, but contrast would remain poor.
If you view a specimen at 40X total magnification with a 10X ocular lens, then you are viewing the specimen with what objective?
Which of the following statements describes true motility?
Movement that appears to be directed from one position to another
Which of the following describes Brownian movement?
Vibratory movement of cells due to their bombardment by water molecules
Why are unstained bacterial specimens more difficult to view than stained specimens?
Stains provide contrast between the cells and the background.
When viewing a hanging drop, it is important to adjust the Abbe condenser using the iris diaphragm. What is the function of this part of the microscope?
The Abbe condenser regulates the amount of light that passes upward from the light source and into the lens system.
Which statement is NOT true regarding protozoa?
Single-celled protozoa are similar in size to bacteria.
What is the advantage of observing a hanging drop, compared to a wet mount preparation?
Motility and larger organisms are better viewed in a hanging drop due to the greater depth.
When viewing an unstained, live specimen, how do you distinguish between true motility and Brownian movement?
True motility appears to be directed from one position to the next; Brownian movement appears as vibratory movement around a certain position that occurs at a constant rate.
Which of the following describes an advantage of observing stained rather than unstained bacterial specimens?
Stained preparations are heat fixed and adhere well to the slide.
Which of the following statements is CORRECT regarding the relative sizes of bacteria compared to protozoa and algae?
Prokaryotic bacterial cells are smaller than eukaryotic protozoa and algae.
Which of the following represents an INCORRECT association between a species of bacteria and its cellular morphology?
Which of the following types of organisms are composed of eukaryotic cells?
Diatoms, Volvox and Paramecia
scanning electron microscopes and transmission electron microscopes
To view viruses and the internal structure of bacterial cells, as well as fine structural details of eukaryotic cells
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.
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.
is useful for viewing fine structural details in cross-sections of microorganisms.
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 3-dimensional shape of a protozoan and the arrangement and distribution of cilia on its surface
determining the 3-dimensional shape and arrangement of bacterial cells
transmission electron microscope
viewing ribosomes (20nm) within a bacterial cell
viewing a cross section of poliovirus (30nm)
viewing the layers of the gram-negative cell wall in cross section
confirming the 9 + 2 microtubule arrangement in a eukaryotic flagellum
Chlamydia trachomatis elementary bodies measure approximately 0.25 micrometers in diameter. What is this measurement expressed in nanometers (nm)?
250 nm. To obtain the measurement in nanometers, you have multiplied the measurement in micrometers by 1000.
A paramecium is approximately 150 micrometers in length. What is this measurement expressed in millimeters (mm)?
0.15 mm. To obtain the measurement in millimeters, you have divided the measurement in micrometers by 1000.
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
What is the role of lenses in microscopy?
Lenses focus either light or electrons to create a magnified image of a specimen.
Which microscope is used to see internal structures of cells in a natural state?
You are studying a cell structure that is approximately 100 nm in size. Which of the following provides the lowest magnification you can use to see this structure?
scanning electron microscope
What structure does light pass through after leaving the condenser in a compound light microscope?
This microscope produces an image of a light cell against a dark background; internal structures are NOT visible.
Which microscope takes advantage of differences in the refractive indexes of cell structures?
Why is a specimen smaller than 200 nm not visible with a light microscope?
Anything smaller than 200 nm cannot interact with visible light.
What happens to the light rays when they hit the specimen in light microscopy?
They are reflected, refracted, or absorbed by the specimen.
In a typical brightfield microscope (seen in the animation), at which point does magnification begin?
The objective lens
When an object is viewed through a light microscope with oculars that magnify 20x and a high-power objective lens that magnifies 100x, what is the total magnification of the object?
) In microscopy, the term resolution
refers to the ability to distinguish fine structure and detail in a specimen.
A student is looking at a bacterial specimen using the oil immersion lens, but has forgotten to put immersion oil on the slide. The specimen will appear
somewhat fuzzy and have poor resolution.
Which of the following types of microscopes is best used for observing the surfaces of intact cells and viruses?
scanning electron microscope
Which microscope is used to observe a specimen that emits light when illuminated with an ultraviolet light?
In using this microscope, the observer does NOT look directly at an image through a lens.
The limit of resolution of the compound microscope illuminated with visible light is approximately 0.2 μm.
Which of the following types of microscopy provides advantages for viewing live images?
darkfield microscopy.Darkfield microscopy allows colorless cells to be visualized without applying stains that kill cells
Which of the following correctly traces the path of light through the compound microscope?
light source; condenser; specimen; objective lens; ocular lens
Why do electron microscopes have higher resolving power than light microscopes?
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?
Which type of microscope would allow the viewer to see ribosomes inside a cell?
transmission electron microscope
Which of the following is a characteristic shared by both electron and light microscopes?
They both employ the use of objective lenses.
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.
Which of the following types of microscope is used to observe viruses and the internal structure of thinly sectioned cells?
transmission electron microscope
What is the total magnification of a specimen viewed with a 10x ocular lens and a 45x objective lens?
Which of the following characteristics are shared by Enterococcus and Streptococcus?
Which of the following techniques would allow you to easily differentiate between Staphylococcus and Enterococcus?
Which of the following are found primarily in the intestines of humans?
facultatively anaerobic gram-negative rods
You have isolated a bacterium that grows in a medium containing an organic substrate and nitrate in the absence of oxygen. The nitrate is reduced to nitrogen gas. You can be sure that this bacterium is
using anaerobic respiration.
How are negative stains different from other types of stains?
They stain the background, leaving the cells colorless.
Following an endospore stain, how does one distinguish endospores from vegetative cells?
Vegetative cells are pink, endospores are green.
What is the fundamental purpose of staining in light microscopy?
To increase the contrast and visibility of the specimen
Which biologist introduced the term prokaryote in 1937 to distinguish cells with no nucleus from the nucleated cells of plants and animals?
The cell walls of bacteria are responsible for the shape of the bacteria and the difference in the Gram stain reaction.
Which of the following types of bacterial cells would have flagella located at only one end of the cell?
Lophotrichous and monotrichous
Which of the following statements about bacterial flagella is true?
Flagella can rotate 360 degrees.
Which of the following terms refers to a bacterium moving towards a light source?
How do axial filaments differ from regular bacterial flagella?
The axial filament is located between the cell membrane and the outer membrane.
What is the advantage to spirochetes of the corkscrew movement provided by axial filaments?
It allows the cells to move more easily through viscous human tissues and fluids, such as mucus.
Which structure acts like an invisibility cloak and protects bacteria from being phagocytized?
cell is a body with long multiple tails coming out of one end of the cell body
You have isolated a motile, gram-positive cell with no visible nucleus. You can safely assume that the cell
has a cell wall.
If you observe rod-shaped red cells after the Gram stain, you can assume their cell walls contain endotoxin.
Why is ATP necessary for active transport?
ATP provides energy to transfer material against its concentration gradient.
Which transport protein employs transporters that move molecules only in one direction?
Uniport and Symport
Which type of active transport protein uses one protein to pump two different molecules?
Antiport and Symport
How does water enter and exit a cell?
By simple diffusion or by use of an integral transport protein
is a type of peripheral protein above that can be used as a receptor or in enzymatic functions.
circular chromosome, not enclosed in nuclear envelope
flagella that rotate, composed of flagellin
peptidoglycan-containing cell wall
rough endoplasmic reticulum
linear chromosome enclosed in nuclear envelope
flagella that wave, composed of microtubules
cellulose or chitin-containing cell wall
Select the structures below that are found in all bacterial cells.
The number of organelles such as chloroplasts, mitochondria, and rough endoplasmic reticulum is the same in all eukaryotic cells.
Analysis of the second swab has confirmed that the causative organism is Streptococcus pyogenes, a gram-positive organism. Imagine that you are the technician looking at the Gram stain from Shelly's culture. What would you expect to see as you look through the microscope?
purple, spherical-shaped organisms arranged in chainlike formations. The purple color indicates a gram-positive organism. Recall that the purple color is due to the retention of the crystal violet-iodine (CV-I) complex in the thick peptidoglycan layer of the gram-positive organism. As the name Streptococcus implies, S. pyogenes is spherical (coccoid) in shape and remains in a chainlike formation after dividing.
You are observing a Gram stain of spherical-shaped microorganisms that are linked in a chain and stain purple. How would you describe these bacteria using the correct terminology for the cell shape and arrangement?
gram-positive streptococci. Gram-positive cells stain purple, and the term streptococci indicates a chain of spherical-shaped cells.
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