Practicals

• What are limitations of the pH practical?

  Samples are only taken every 30s. Time taken for reaction to take place is only approximate.
• 1. Place one drop of iodine solution into each well of a spotting tile.
  2. Take 3 test tubes. One with 2cm of starch solution, 2cm of amylase solution and 2cm of pH 5 solution.
  3. Place all test tubes in a water bath at 30 degrees for 5-10 mins so temp can equilibrate.
  4. Combine each solution into one test tube and place it into the waterbath again and start a stopwatch.
  5. After 30s, use the glass rod to place one drop of the solution into a well of the spotting tile. It should turn blue-black because starch is present.
  6. Repeat 5) every 30s until iodine is orange. Repeat using different pH values.
• Why do you have to leave the amylase solution in water for 5 minutes?

  To allow the starch and amylase to equilibrate to the temperature of the water bath
• Explain how to investigate the effect of light intensity on photosynthesis.

  1. Place a boiling tube 10cm away from a light source. Fill the boiling tube with a fixed volume of sodium hydrogen carbonate solution (releases carbon dioxide)
  2. Place pondweed into the boiling tube with a cut end at the top. Leave the boiling tube for 5 mins to acclimatise the conditions in the boiling tube.
  3. Start the stopwatch and count the number of bubbles (oxygen) produce in 1 minute. Repeat 2 times then calculate and record a mean.
  4. Repeat the experiment but increase the distance.
• How can you use a tube with bubbles to measure the rate of photosynthesis?

  Measure the amount of bubbles in a given time.
• How does repeating an experiment improve practicals?

  It gives more representative/reliable results to identify anomalies.
• Name the gas produced by the pondweed in the light.

  Oxygen
• Describe one way the student could change the intensity of light

  reaching the pondweed.

  Using a lamp or light source and change the distance, moving it closer to the pondweed.
• What could you do to make sure heat from the lamp does not affect the rate of photosynthesis?

  • Use LED lamp
  • Place pondweed in a water bath or beaker of water
• Suggest two ways the method could be improved to measure the rate of photosynthesis more accurately.


  Measure the volume of gas with a measuring cylinder or gas syringe in an increased length of time.
• 1. Peel off potato skin and use a cork borer to make identical cylinders. Use a scalpel to cut each cylinder to 3cm.
  2. Measure and record the mass and length of each cylinder.
  3. In one test tube, add 10cm^3 of 0.5 sugar solution. Next, add 10cm^3 of 0.25 sugar solution. Then, add 10cm^3 of distilled water.
  4. Leave the cylinders in each test tube overnight.
  5. Remove each cylinder and pat dry with a paper towel to remove surface moisture.
  6. Measure the mass and length again and calculate a percentage change.
  7. Plot a graph of change in mass against concentration of sugar solution with sugar solution.
• The change in mass should be on the y-axis and the sugar solution should be on the x-axis.
• How do you measure the rate of photosynthesis?

  • Allow the plant to equilibrate in light
  • Collect the gas produced using a measuring cylinder
  • Start a timer to measure how long it take for the gas to be collected
  • Repeat and calculate a mean