microscopy

• light microscopes

  use light and lenses to form an image of a specimen and magnify it
• what do light microscopes let us see

  individual cells and large subcellular structures eg nuclei
• electron microscopes

  use electrons instead of light to form an image. they have much higher magnification than light microscopes. they also have a higher resolution
• what do electron microscopes let us see

  much smaller things in more detail eg the internal structure of mitochondria and chloroplasts. they even let us see tinier things like ribosomes and plasmids
• what is the formula for magnification

  magnification = image size / real size
• what is the method to prepare your slide

  1. add a drop of water to the middle of a clean slide
  2. cut up an onion and separate it out into layers. use tweezers to peel off some epidermal tissue from the bottom of one of the layers
  3. using the tweezers, place the epidermal tissue into the water on the slide
  4. add a drop of iodine solution
  5. place a cover slip on top. to do this, stand the cover slip upright on the slide, next to the water droplet. then carefully tilt and lower it so it covers the specimen. try not to get any air bubbles under there - they‘ll obstruct your view of the specimen
• what are the parts of a light microscope


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• how to use a light microscope to look at your slide

  1. clip the slide you’ve prepared onto the stage
  2. select the lowest-powered objective lens
  3. use the coarse adjustment knob to move the stage up to just below the objective lens
  4. look down the eyepiece. use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
  5. adjust the focus with the fine adjustment knob, until you get a clear image of what’s on the slide
  6. if you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus