Required practicles

• Equipment


  • Light microscope
  • Microscope slide
  • Cover slip
  • Onion
  • Forceps
  • Iodine solution
  • White tile
  • Scalpel
  • Any other prepared plant and animal cell slides
• Microscopy method


  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

  7. Turn the nosepiece to select a low power objective

  8. Set up the microscope - don't look into the eyepiece yet. Instead, use the coarse adjustment knob to raise the stage until the cover slip just touches the objective

  9. Now look into the eyepiece and turn the coarse adjustment knob to move the stage away until the image comes into focus (doing this helps avoid you breaking the slide)

  10. Turn the nosepiece to select a high power objective

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

  12. Make a labelled drawing of a few of the cells you can see, including any features eg. cell wall, nucleus. Write down the magnification

  13. Repeat these steps using a prepared slide
• Equipment

  • agar plate
  • heatproof mat
  • filter paper discs
  • three antiseptics eg. mouthwash, TCP, and antiseptic cream
  • disinfectant bench spray
  • 1% Virkon disinfectant
  • Antibacterial handwash
  • forceps
  • clear tape
  • hand wash
  • wax pencil or permanent marker
  • incubator set to 25°C
• Method

  1. Spray the bench you are working on with disinfectant then wipe dry with paper towels

  2. On the bottom of the agar plate (not the lid) mark with a wax pencil / permanent marker: 3 segments, a dot in the middle of each segment, your initials, date, name of bacteria

  3. Wash your hands with antibacterial handwash

  4. Place the different antiseptics onto different filter paper discs

  5. Lift the lid of the agar plate at an angle carefully and use forceps to place each filter paper disc onto the dots. Note down the antiseptic applied to each zone

  6. Tape the lid onto the agar plate securely, but loosely enough that oxygen can still reach the bacteria

  7. Place the agar plate in the incubator at 25°C for 48 hours

  8. Measure the diameter of the clear zones after 48 hours using a ruler. Take a second measurement at 90 degrees from your first measurement and take a mean for the diameter. Do not remove the lid when taking measurements

  9. Record the results in a table
• Extension

  • Repeat the procedure with different concentrations of the same antiseptic on the filter paper discs to investigate the optimum concentration of antiseptic used to kill bacteria
• Carrying out chemical tests for carbohydrates, proteins and lipids

  1. Grind food sample with distilled water using mortar and pestle to make a paste

  2. Transfer paste to beaker and add more distilled water

  3. Stir to dissolve chemicals

  4. Filter solution to remove suspended food particles
• Carbohydrates


  Include starch and sugars such as glucose
• Test for starch


  1. Place 2cm3 of food solution in test tube

  2. Add a few drops of iodine solution

  3. Blue-black colour indicates presence of starch

  4. Orange colour indicates no starch
• Test for sugars (e.g. glucose)

  1. Place 2cm3 of food solution in test tube

  2. Add 10 drops of Benedict's solution

  3. Heat test tube in hot water bath for 5 minutes

  4. Green colour = small amount of sugar

  5. Yellow colour = more sugar

  6. Brick red colour = a lot of sugar
• Reducing sugars


  • Sugars that the Benedict's test works for (e.g. glucose)
  • Non-reducing sugars (e.g. sucrose) do not work with Benedict's test
• Test for proteins


  1. Place 2cm3 of food solution in test tube

  2. Add 2cm3 of Biuret solution

  3. Purple/lilac colour indicates presence of protein
• Test for lipids/fats


  1. Grind food with distilled water using mortar and pestle (do not filter)

  2. Transfer 2cm3 of solution to test tube

  3. Add a few drops of distilled water and ethanol

  4. Shake gently

  5. White cloudy emulsion indicates presence of lipids
• Ethanol is highly flammable, so no naked flames should be present