Required practical 2

• Describe how to prepare squashes of cells from plant root tips

  1. Cut a thin slice of root tip (5mm from end) using scalpel and mount onto a slide
  2. Soak root tip in hydrochloric acid then rinse
  3. Stain for DNA eg. with toluidine blue
  4. Lower coverslip using a mounted needle at 45C without trapping air bubbles
  5. Squash by firmly pressing down on glass slip but do not push sideways
• Why are root tips used?

  ● Where dividing cells are found / mitosis occurs
• Why is a stain used?

  ● To distinguish chromosomes

  ● Chromosomes not visible without stain
• Why squash / press down on cover slip?

  ● (Spreads out cells) to create a single layer of cells

  ● So light passes through to make chromosomes visible
• Why not push cover slip sideways?

  ● Avoid rolling cells together / breaking chromosomes
• Why soak roots in acid?

  ● Separate cells / cell walls

  ● To allow stain to diffuse into cells

  ● To allow cells to be more easily squashed

  ● To stop mitosis
• 
  

  1. Clip slide onto stage and turn on light
  2. Select lowest power objective lens (usually x 4)
  3. Use coarse focusing dial to move stage close to lens
  4. Turn coarse focusing dial to move stage away from lens until image comes into focus
  5. Adjust fine focusing dial to get clear image.
  6. Swap to higher power objective lens, then refocus 15
• Describe how to set-up and use an optical microscope

  1. Clip slide onto stage and turn on light
  2. Select lowest power objective lens (usually x 4)
  3. Use coarse focusing dial to move stage close to lens
  4. Turn coarse focusing dial to move stage away from lens until image comes into focus
  5. Adjust fine focusing dial to get clear image.
  6. Swap to higher power objective lens, then refocus

  
• What are the rules of scientific drawing?

  ✓ Look similar to specimen / image

  ✓ No sketching / shading - only clear, continuous lines

  ✓ Include a magnification scale (eg. x 400)

  ✓ Label with straight, uncrossed lines