2.1.1 (a-f) - Microscopy & Staining Flashcards Preview

OCR A Biology A Level - Chapter 2 > 2.1.1 (a-f) - Microscopy & Staining > Flashcards

Flashcards in 2.1.1 (a-f) - Microscopy & Staining Deck (8)
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1. How is a dry mount prepared?

2. How is wet mount prepared?

3. How is a smear slide prepared?

  1. Specimens are sectioned (cut into thin slices) and placed on the slide, place a cover slip on top
  2. Suspend the specimen in a liquid. At an angle place the cover slip on (to keep bubbles out)
  3. Prepare a wet mount, then use the edge of a slide to smear the sample and place a cover slip on top


What is the purpose of staining and what are the 2 types?

  • Some cells let light fall through, not enough contrast to see the ultrastructure
  • Some stains are specific to different tissues/organelles
    • Such as acetic orcein stains chromosomes red

Differential Staining Techniques

Gram Staining

Acid Fast Technique


How does gram staining work?

  • When stained with iodine or crystal violet, gram positive bacteria shows up blue/purple under a microscope
  • Gram negative bacteria will lose the original iodine/crystal violet stain, so they are counterstained and appear red/pink


How does the acid fast technique work?

  • Cells are dyed in carbolfuchsin
  • They are washed in dilute acid/alcohol
  • Mycobacterium are not affected, retain the carbolfuchsin dye and appear red
    • Other bacteria need a counterstain and appear blue as they lose the carbolfuchsin


What are the pros and cons to using light or electron microscopes?


  • Cheap, user-friendly
  • Can use living samples
  • However, has limited resolution


  • High resolution
  • SEM shows 3D images
  • TEM shows detailed ultrastructure
  • Require trained operators
  • Sample must be dead and dried (or an artefact may be present)
  • In black and white


What are the pros and cons to using laser confocal scanning microscopes?

  • Can use living samples
  • Relies on computers to piece together information from dots of light
    • ​The image is an interpretation rather than a real image







Magnification: How many times larger an image is than the actual object

Resolution: The ability to see individual objects/structures as separate entities


How do you calibrate a microscope using an eyepiece graticule?

  1. Put the Stage Micrometer and Eyepiece Graticule in place
  2.  Get the scale of the micrometer in clear focus
  3. Align the micrometer scale with the eyepiece scale, take a reading.
  4. 100 small divisions are 1mm, so 1 division is 10um.
  5. Work out the magnification of the lens.
  6. Replace the stage micrometer with a specimen and measure using the eyepiece graticule.