Biology required practicals

• Microscopy


  1. Use a scalpel and tweezers to prepare a thin layer of onion skin

  2. Add a drop of iodine to stain the cells

  3. Place a cover slip on top

  4. Place the slide on the microscope stage

  5. Start with the shortest objective lens and use the coarse and fine focus knobs to bring the specimen into focus

  6. Change to a higher magnification objective lens and refocus if needed

  7. You can use a graticule (tiny ruler) to measure cell size in micrometers
• Quadrats


  1. Use a random number generator to choose grid positions to place the quadrat

  2. Count the number of the chosen organism inside each quadrat

  3. Calculate the mean number per square meter

  4. Multiply the mean by the total area to estimate the total population

  5. You can also use a transect line to see how population density varies with distance
• Microbiology


  1. Spot different bacterial cultures on agar in a petri dish and observe how they grow

  2. Spread a culture over the agar to make a lawn and then add antibiotic discs

  3. Use aseptic technique - sterilize equipment, work near a Bunsen flame, etc.

  4. Incubate for days and then measure the diameters of colonies or areas with no bacteria
• Decay


  1. Measure out a volume of milk or cream and add sodium carbonate and phenolphthalein indicator

  2. Add the enzyme lipase and use a water bath to maintain a certain temperature

  3. Time how long it takes for the solution to decolorize as the milk decays

  4. Plot the time taken against temperature and identify the optimum temperature