Preparing biological samples for examination

• Aims of the experiment

  • to stain cells for examination with a light microscope
  • to examine a range of cells and other structures with a microscope to understand their basic structure
• Method: animal cells - cheek cells

  1. put a small drop of water on the microscope slide
  2. gently swab the inside of your mouth with a clean cotton bud
  3. gently rub the cotton bud in the drop of water. You will be able to see the cells with the naked eye
• Method : Plant cells - onion epidermal cells

  1. put a small drop of water on the microscope slide
  2. peel some onion skin from inside one of the leaves in an onion bulb
  3. use forceps to transfer to the drop of water. Make sure that the onion skin is flat, and there are no trapped air bubbles. Stain cells with iodine
• Method : Other biological structures - humain hair or fur

  1. put a small drop of glycerol on the microscope slide. Glycerol has a very similar refractive index to hair, so you will be able to see the layers in the hair with the microscope
  2. cut a small piece of the hair or fur
  3. use forceps to transfer to a drop of glycerol
• Completing the microscope slide for examination

  • when viewing any slide with a microscope, a small square or circle of thin glass called a coverslip is placed over the specimen
  • it protects the microscope
  • prevents the slide from drying out when it's being examined
  • it is important that no air bubbles are trapped underneath
• Mounted needle

  • a needle mounted in a wooden or metal handle
  • for use in microscope work or dissection
• Staining the cells

  • most cells are colourless
  • used to add contrast
  • certain stains used to stain specific cell structures or cell products
• Staining the cells : method

  1. place a small square or circle of thin glass called a coverslip over the specimen
  2. put a drop of the stain on the slide, next to the coverslip
  3. draw the stain under the coverslip by placing a piece of filter paper next to it
• Risks

  • care must be taken when looking down the microscope if the illumination is too bright
  • care must be taken when using microscope stains
  • care must be taken when handling coverslips, microscope slides and mounted needles