required practicals

• (2) osmosis

  1. cut potato into identical cylinders & get beakers with different sugar solutions in them
  2. measure mass of cylinders, leave one cylinder in each beaker for 24 hours
  3. take out & dry with paper towel & measure mass
  4. if water drawn in by osmosis : increased mass - if drawn out, they'll have decreased
  5. calculate % change in mass & plot graph
  6. repeat experiment & calculate mean % at each concentration
• (3) Enzymes

  1. drop of iodine solution in every well of spotting tile
  2. bunsen burner on mat, tripod & gauze over. Put beaker of water on tripod & heat until 35 degrees
  3. add 1cm3 of amylase & a buffer solution with pH of 5 to boiling tube
  4. put tube into beaker of water & wait 5 minutes
  5. add 5cm3 of starch solution to the boiling tube - mix & start a stopwatch
  6. use continuous sampling to record how long it takes for amylase to break down starch - when iodine solution remains orangey-brown, starch not present
• Food tests: Benedict's for sugars

  1. prepare food sample & transfer 5cm3 to a test tube
  2. prepare water bath : set to 75 degrees
  3. add Benedict's solution to test tube (10 drops)
  4. put test tube in water bath & leave for 5 minutes
  5. if food sample contains reducing sugar, solution will change from blue to green/yellow/brick-red depending on volume of sugar
• Food tests : Iodine for starch

  1. make a food sample & transfer 5cm3 to test tube
  2. add few drops of iodine solution & shake to mix
  3. if sample contains starch, solution from browny-orange to black/blue-black
• food tests : Biuret for proteins

  1. prepare sample & transfer 2cm3 to test tube
  2. add 2cm3 of Biuret solution to sample & mix
  3. if sample contains protein, solution will change from blue to pink/purple
• food tests : Sudan III test for lipids

  1. prepare food sample but don't filter it. Transfer 5cm3 to test tube
  2. add 3 drops of sudan III stain solution to test tube & shake
  3. the solution stains lipids : if contains lipids, mixture will separate out into 2 layers
  4. top will be bright-red. If no lipids; no separate red layer formed
• (5) Photosynthesis

  1. take boiling tube & place 10 cm away from LED source
  2. fill boiling tube with sodium hydrogen carbonate - release CO2
  3. put pondweed into boiling tube with cut end at the top - leave for 5 minutes to acclimatise
  4. start stopwatch & count no. of bubbles in 1 minute
  5. repeat 2x & calculate mean bubbles
  6. do experiment again with different distances between tube & light source
  7. calculate using inverse square law
  8. to increase accuracy : pondweed under funnel & gas catch in measuring cylinder - use it to measure volume of oxygen produced
• (1) microscopy

  1. Add a drop of water to the slide

  2. Place small layer of onion epidermal tissue into water on slide

  3. Add a drop of iodine solution on top

  4. Place a cover slip on top

  5. Place the slide on the stage underneath the clips

  6. Select the lowest power objective lens (there is normally 4x, 10x and 40x)

  7. Turn the coarse adjustment knob until the lens nearly touches the slide

  8. Observe the specimen through the eyepiece, adjust fine adjustment knob and change objective lenses t0 get the clearest view