core practicals

• making cultures with aseptic technique (core practical)

  1. lift lid of petri dish towards flame (to sterilise air by killing microbes)
  2. put drop of culture on agar evenly
  3. put drops of antibiotics on culture
  4. tape it (to allow for aerobic respiration)
  5. incubate at 25 degrees celcius
  6. measure size of cultures with NO bacteria with πr^2 or πr^2 / 4
• OSMOSIS

  1. weight and place identical cylinders from same vegetable in sugar solutions of varying concentrations
  2. after set time, remove excess water and re-weigh
  3. calculate percentage change in mass
  4. plot a graph of change in mass against concentration and draw a LOBF
• microscopy practical

  1. peel off an epidermal layer of the onion using forceps
  2. mount onto the slide carefully
  3. add two drops of iodine to stain the cells
  4. place the cover slip on top
  5. rotate the objective lens accordingly
  6. bring the stage as close to the objective lens as possible
  7. focus the slide and record the image
• food tests

  1. starch - iodine - orange to black
  2. sugar - benedict's - blue to red
  3. protein - biuret - blue to lilac
  4. lipids - ethanol - cloudy emulsion
• effect of pH on amylase

  1. place one drop of iodine in each well of a spotting tile
  2. 3 test tubes, one filled with starch solution, one with amylase, and another with pH buffer
  3. put each tube in water bath to reach the same temperature to ensure accuracy
  4. now add all three solutions into one test tube, return to the water bath and start a stopwatch
  5. after 30 seconds, transfer one drop of the new solution to a well in the spotting tile and it should turn blue-black
  6. continue every 30 seconds until iodine remains orange, meaning no more starch is present
  7. repeat with different pH buffers
• photosynthesis

  1. take a boiling tube and place it 10cm away from a light source
  2. fill the tube with sodium hydrogen carbonate solution (releases carbon dioxide)
  3. put a piece of pondweed into the tube with the cut end at the top
  4. leave in for five minutes to acclimate to the conditions of the tube
  5. start a stopwatch and count the number of bubbles produced in a minute
  6. repeat this twice to calculate mean
  7. repeat whole experiment, increasing the distance of the light source by 10cm each time