Microscope practical

• Observing onion cells under a microscope


  1. Carefully peel off a layer of onion cells using the tweezers

  2. Carefully put the onion skin on a microscope slide

  3. Add a drop of water if needed to unroll the sheet of cells

  4. Add a drop of iodine to stain the cell walls brown (use goggles)

  5. Put a thin coverslip over the top to make sure that the cells are flat

  6. Dab with a paper towel to remove any excess iodine that comes out of the edges of the coverslip

  7. Clip onto the microscope stage

  8. Adjust the mirror so that enough light passes through the slide

  9. Look under low power first because it is easier to focus on cells

  10. Then move up to higher powers to see more detail
• Draw clearly using lines without shading, and add a title and the magnification to your diagram
• the objective lens is the one that magnifies the image
• total magnification = objective lense + ocular lense
• the eyepiece has a lower magnifying power than the objective lenses but allows us to look at the specimen from above
• the ocular lens is the eyepiece which has a fixed power of x10