Microscopes

• Label the diagram

  A) eyepiece

  B) objective lens

  C) coarse focus

  D) fine focus

  E) arm

  F) stage

  G) stage click

  H) condenser

  I) mirror

  
• Microscopes let us see things that we can't see with the naked eye.
• Light microscopes use light and lenses to form and image of a specimen and magnify it. They let us see individual cells and large subcellular structures, like nuclei.
• Electron microscopes use electrons instead of light to form an image. They have a much higher magnification than light microscopes. They also have a higher resolution. (Resolution is the ability to distinguish between two points, so a higher resolution gives a sharper image.)
• Electron microscopes let us see much smaller things in more detail, like the internal structure of mitochondria and chloroplasts. They let us see tinier things like ribosomes and plasmids.
• Magnification = image size/real size
• A slide is a strip of clear glass or plastic onto which the specimen is mounted.
• How to prepare a slide to view onion cells:

  • Add a drop of water to the middle of a clean slide
  • Cut up an onion and separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of the layers.
  • Using the tweezers, place the epidermal tissue into the water on the slide.
  • Add a drop of iodine solution. This will highlight the objects in the cell.
  • Place a cover slip on top. Try not to get any air bubbles under there, it will obstruct your view of the specimen.
• Iodine is a stain. Stains are used to highlight objects in a cell by adding colour to them.
• How to use a light microscope to look a slide:

  • Clip the slide you've prepared onto the stage.
  • Select the lowest-powered objective (the one that produces the lowest magnification)
  • Use the coarse adjustment knob to move the stage up to just below the objective lens.
  • Look down the eyepiece. Use the coarse objects knob to move the stage downwards until the image is roughly in focus.
  • Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide.
  • If you need to see the slide with greater magnification, swap to a higher-powered objective lens and refocus.
• Draw your observations neatly with a pencil

  • Draw what you see under the microscope using a pencil with a sharp point.
  • Make sure your drawing takes up at least half of the space available.
  • Your drawing should not include any colouring or shading.
  • If you are drawing cells. the subcellular structures should be drawn in proportion.
  • Remember to include a title of what you were observing and write down the magnification that it was observed under.
  • Label the important features of your drawing (nucleus, chloroplasts, etc) using straight, uncrossed lines.