required practical: microscopy

• Describe how you would prepare a microscope slide for analysis

  1. Peel off epidermal layer using forceps

  2. Place sample on drop of water on microscope slide

  3. Add drops of iodine solution to sample

  4. Lower cover slip onto sample using mounting needle
• Describe how you would prepare a microscope slide using onion tissue

  1. Peel off epidermal layer using forceps

  2. Place sample on drop of water on microscope slide

  3. Add drops of iodine solution to sample

  4. Lower cover slip onto sample using mounting needle
• Thin sample of tissue

  Allows light to pass through so internal structures can be observed
• Water added to slide before sample

  Allows the sample to be suspended between the slide and the cover slip, and ensures the cover slip stays in place
• Iodine solution added

  Adds contrast - reacts with starch in plant cells and turns blue-black; allows internal structures (e.g. nucleus) to become more visible
• Cover slip lowered using mounting needle

  Ensures that no air bubbles are trapped
• Measure the length of a cell viewed under the microscope

  Measure using eyepiece graticule and calibrate with stage micrometer
• Calculate the magnification of an image

  Magnification = observed cell length / actual cell length
• Wear safety goggles when handling iodine solution