more micro lecture 2

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more micro lecture 2
2014-09-29 22:11:15

chapt 4
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  1. What is the role of lenses in microscopy?
    Lenses focus either light or electrons to create a magnified image of a specimen.
  2. Why is a specimen smaller than 200 nm not visible with a light microscope?
    Anything smaller than 200 nm cannot interact with visible light.
  3. What happens to the light rays when they hit the specimen?
    They are reflected, refracted, or absorbed by the specimen.
  4. What is the role of the ocular lens?
    To recreate the image in the viewer’s eye
  5. What is meant by light rays being divergent?
    It is spreading out
  6. In a typical brightfield microscope (seen in the animation), at which point does magnification begin?
    The objective lens
  7. Why do electron microscopes have higher resolving power than light microscopes?
    Electrons have a smaller wavelength than visible light, leading to higher resolution.
  8. Which of the following is a lens found on electron microscopes but not on light microscopes?
    Projector lens
  9. Which type of microscope would allow the viewer to see ribosomes inside a cell?
    A transmission electron microscope
  10. Which of the following is a characteristic shared by both electron and light microscopes?
    They both employ the use of objective lenses.
  11. 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.
  12. A student from one of the research labs is having trouble preparing a slide for examination and photographing. The bacterial slide that he has brought to you was prepared using a commercially purchased stain. He has asked for your help in determining what he is doing wrong so that he can change the lab protocols and continue on with his project. After examining the slide under oil immersion, you determine that no bacteria are present even though the student is able to show you the culture he used to make that slide that has visible growth in the liquid medium.
    • Which of the following statements does NOT explain the fact that there are no bacteria present on the student’s slide?
    • Rinsing with alcohol during the washing step stripped the bacteria off the glass slide.
  13. You volunteer to help the student with his fixation technique and in choosing a proper stain for the project he is working on. After watching and helping the student correct any problems with his fixation technique, you now need to determine which stains to use. The single criterion for the project is to be able to determine cell shape and size in a pure broth culture after some treatments. No differentiation between cell types is required (i.e., Gram-positive or Gram-negative), so you want to convince the student that a simple stain would be his best option. The charged dyes used in simple staining will penetrate the bacterial cell and will be retained after rinsing the slide with water to remove surplus dye.
    • Which staining procedure would be best to use to stain the slides required for this student’s project? Why?
    • The positively charged methylene blue will be attracted to the negatively charged components of the cell wall and will be retained.
  14. While staining a mixed culture of Gram-positive and Gram-negative bacteria, switching the order of steps 2 and 3 would result in ______________________.
    all bacteria appearing pink
  15. Which structural feature of Gram-positive bacteria enhances their ability to retain the crystal violet dye?
    a thick peptidoglycan layer
  16. What would you anticipate seeing if you accidentally switched crystal violet and safranin while performing a Gram stain?
    All bacteria would appear purple.
  17. What would you expect to see if you forgot to perform step 2 of the Gram stain procedure?
    All bacteria would appear pink.
  18. How are negative stains different from other types of stains?
    They stain the background, leaving the cells colorless.
  19. Which of the following is an example of a dye used in a simple stain?
    Methylene blue
  20. How does the malachite green stain enter an endospore?
    It is heated.
  21. Following an endospore stain, how does one distinguish endospores from vegetative cells?
    Vegetative cells are pink, endospores are green.
  22. What is the fundamental purpose of staining in light microscopy?
    To increase the contrast and visibility of the specimen
  23. Why is the unknown in this example not Pseudomonas?
    It ferments lactose.
  24. What test result indicates that the unknown can utilize citrate as its sole carbon source?
    The medium turns blue.
  25. How would the results be different if this organism was Salmonella?
    It would produce hydrogen sulfide.
  26. How is fermentation of lactose detected?
    The drop in pH turns the indicator dye yellow.
  27. How many questions are needed in this dichotomous key to determine if the unknown is Bacteroides?
  28. Why is visualization not sufficient to properly identify bacteria?
    Bacteria have a limited set of shapes and many unrelated bacteria share the same shape.
  29. What is the hallmark of dichotomous keys?
    They consist of a series of paired statements, in which only one statement of each pair applies to a given organism.
  30. Biochemical tests _________________.
    are the main methods used to identify unknown bacteria
  31. How many answers are there to a question in a dichotomous key flowchart?
  32. Why are flowcharts useful for dichotomous keys?
    They allow the researcher to visualize relationships between different bacteria.
  33. The first question in this dichotomous key addresses
    Gram stain differences.
  34. Staining is an important way to improve which of the following aspects of microscopy?
    resolution and contrast
  35. Which of the following types of microscopes reveals the surface features of small molecules?
    an atomic force microscope
  36. If you needed to look at the fine details of the interior of a virus, which microscope would you use?
    transmission electron microscope
  37. What is an example of a negative stain?
    a capsule stain
  38. Which of the following does NOT stain the bacterial cell?
    the negative stain
  39. A microbiologist is using heat to drive the stain carbolfuchsin into a smear. Which of the following staining procedures is the microbiologist using?
    the acid-fast stain
  40. Put the following steps of bacterial specimen preparation and staining in order: a. fixation b. application of staining dyes c. smear preparation
    c, a, b
  41. Plaques are associated with which of the following methods of laboratory identification of microorganisms?
    phage typing
  42. Which of the following groups of organisms belongs in the domain Eukarya?
  43. Which of the following is one-billionth of a meter?
    a nanometer
  44. Which of the following is NOT equal to 50 millimeters?
    5,000,000 nanometers
  45. Which of the following types of microscopes can magnify more than 2000×?
    a transmission electron microscope
  46. Leeuwenhoek's microscopes had a resolution (resolving power) of 1 micrometer. This means that __________.
    the microscope could distinguish objects that were more than 1micrometer apart
  47. A scientist is using an objective lens with 40× magnification on his microscope. If the ocular lens magnifies 10×, what is the total magnification being used to visualize the specimen?
  48. A thin film of microorganisms on a slide is called a __________.
  49. The reagents crystal violet, iodine, and safranin are all associated with which of the following staining procedures?
    the Gram stain
  50. Put the following taxonomic groups in order, from broadest group to most specific group: a. phylum b. genus c. family d. order
    a, d, c, b