The Microscope
Preparing a slide of cheek cells

micros4 Using the microscope:

  1. Select a low power objective lens
  2. Adjust the mirror to produce the best light.
  3. Move the objective lens down towards the slide, looking from the
  4. Focus by moving the lens AWAY from the slide.
  5. Adjust the aperture to produce the best light.

The total magnification is found by multiplying the magnification of the eye
piece by the magnification of the objective lens    ie

 total magnification = eyepiece
magnification x objective lens magnification


eyepiece Objective Total magnification
 10x 20x 200x


Preparing a slide of some cheek cells:

  • Take a clean microscope slide
  • Rub a clean cotton bud around the inside of your mouth and then smear it across the middle of the slide.
  • Add one drop of water and a drop of methylene blue stain(1)
  • Place a cover slip on the drop (at an angle so that there are no air bubbles)
  • Squash it down gently using a piece of blotting paper
  • Place the prepared slide on the microscope stage.
  • Adjust the light source so that it shines through the slide.
  • Focus by turning the focus knob so that the lens moves AWAY from the slide(2)
    1:The stain is a special dye that helps the nucleus and membrane show up better
    2:Tuning the focus knob is sometimes called ‘racking’)

Cheek cells
Note: A micron (short for micrometer) is one-millionth of a meter.
A human hair is about 50 microns wide

The same procedure can be carried out on the thin skin that can be peeled from an onion. The stain is not needed in this case.

Onion cells