1 - Microscopy

• What is the method for this practical? (part 1)

  1. Peel off an epidermal layer on the onion using forceps.
  2. Mount onto the microscope slide with a drop of water using a pipette, making sure the tissue lies flat.
  3. Add 2 drops of iodine solution to stain the cells.
  4. Place the cover slip on by first placing one edge down on the slide and slowly lowering the other side of the cover slip using forceps. Make sure no air bubbles are trapped.
  5. Remove any excess stain by soaking it with paper towels.
  6. Place the slide on the stage of the microscope.
• What is the method for this practical (part 2)?

  7. Turn the nosepiece to select a low power objective.

  8. Use the coarse adjustment knob to raise the stage until the cover slip just touches the objective.

  9. Look into the eyepiece and turn the coarse adjustment knob to move the stage away.

  10. Turn the nosepiece to select a high power objective.

  11. Repeat the same process and then look into the eyepiece and turn the fine adjustment knob until the image comes into focus.

  12. Make a drawing of the cells you can see. Write down the magnification.

  13. Repeat these steps.
• How would you prepare a microscope slide using onion tissue?

  Peel the epidermal layer of the onion, place on a drop of water on a slide, add iodine solution, and lower a cover slip on using a mounting needle.
• Why is a thin tissue sample required?

  Allows light to pass through so internal structures can be observed.
• Why is water added to the slide before the slip is mounted?

  It allows the sample to be suspended between the slide and the cover slip, and insures the cover slip stays in place.
• Why is iodine solution added to stain the cells?

  To make them visible as the iodine solution reacts with starch turning blue—black.
• How would you measure the length of a cell viewed under the microscope?

  Measure using an eyepiece graticule and calibrate with a stage micrometer.
• Magnification = observed cell length/actual cell length
• What safety precaution should be taken during this experiment?

  Wearing goggles.