Bio Skills

• Magnification


  The degree to which the size of an image is larger than the object itself
• Light microscopes used in most schools

  • Magnify about 100 times on low power
  • Magnify about 400 times on high power
• Resolution


  The degree to which it is possible to distinguish between two objects that are very close together
• The human eye can resolve two points that are about 0.1 mm (100 µm) apart
• The maximum resolution of a light microscope is around 0.2 µm, that is about half of the lowest wavelength of the visible light
• Contrast


  The difference in light intensity between the image and the adjacent background
• Contrast can be obtained by staining the material being studied
• Calculating cell size


  Field of view (µm) divided by fit size (how many cells fit across FOV)
• Preparing a 'wet mount'

  1. Fixation

  2. Embedding

  3. Slicing or sectioning

  4. Staining
• The technique should minimise alteration of tissue from living form
• Drawing a scaled diagram

  Scale = actual size of cell divided by size of drawing
• Skills to practise


  • Calculating field of view
  • Drawing a scaled diagram
• 1mm = 1000 µm