Microscopy

• Cells


  • Studied using microscopes
• Light microscopes


  • Use light to form an image of a specimen
  • Magnify to see small cells and large bodily structures
• Electron microscopes

  • Use electrons instead of light to form an image
  • Have a much higher magnification than light microscopes
  • Have a higher resolution (ability to distinguish between fine details)
• Electron microscopes

  • Let us see much smaller things in detail, like the internal structures of mitochondria and chloroplasts
  • Even let us see things like ribosomes and plasmids
• Calculating magnification

  Image size / Real size = Magnification
• Standard form

  Writing very big or small numbers with lots of zeros in a more manageable way, e.g. 0.017 can be written 1.7 x 10^-2
• Converting units

  Remember to convert the units correctly, e.g. 5000 μm = 5 mm
• Preparing a slide to view onion cells

  1. Add a drop of water to the middle of a clean slide

  2. Cut up an onion and separate it out into layers

  3. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers

  4. Place the epidermal tissue into the water on the slide

  5. Add a drop of iodine solution
• Placing the cover slip

  1. Stand the cover slip upright on the slide, next to the water droplet

  2. Carefully tilt and lower the cover slip so it covers the specimen
• Light microscope

  • Use the coarse adjustment knob to move the stage up to just below the objective lens
  • Look down the eyepiece and use the fine adjustment knob to move the image into focus
  • If you need to see the slide with greater magnification, switch to a higher objective lens and refocus
• A light microscope is better than a heavy one