Required Practicals

• In humans, caffeine is a stimulant which increases heart rate by increasing release of excitatory neurotransmitters
• Daphnia are water fleas, used in this case because they have a translucent body through which the heartbeat can be observed, and hence the effect of caffeine on heart rate can be measured
• Equipment needed for daphnia experiment

  • Daphnia
  • Slides
  • Pipettes
  • Distilled water
  • Caffeine solutions
  • Cotton wool
  • Test tubes
  • Stopwatch
  • Filter paper
  • Microscope
  • Camera
• Daphnia Experiment Method

  1. Place some cotton wool (to restrict movement) on a slide.

  2. Add a daphnia.

  4. Use a pipette to add distilled water to the slide.

  5. Put the slide under a microscope.

  6. Record the number of heartbeats in one minute. Repeat to find a mean.

  7. Repeat the experiment with a caffeine solution (use a different daphnia).

  8. Allow the daphnia to acclimatise to the solution.
• Daphnia Graph

  Plot a graph of heart rate against caffeine concentration
• Caffeine increases the heart rate of Daphnia by increasing the release of stimulatory neurotransmitters. As concentration of caffeine increases, heart rate also increases
• It is important to treat the Daphnia ethically during the experiment and release them back into a pond afterwards
• DCPIP


  A redox indicator dye which turns from blue to colourless when it is reduced and accepts electrons
• Vitamin C


  An antioxidant that decolourises DCPIP in its presence
• Decolourisation of DCPIP in the presence of Vitamin C


  Used to measure the Vitamin C content of fruit juice
• Equipment needed

  • DCPIP solution
  • Vitamin C solution
  • Fruit juices
  • Test tubes
  • Pipette
• Experiment Method

  1. Transfer 1cm of DCPIP solution into a test tube with a pipette

  2. Add Vitamin C solution dropwise to the DCPIP solution. Shake after each drop

  3. Record the volume of Vitamin C required to change the colour of the DCPIP

  4. Repeat to find a mean

  5. Repeat the experiment with fruit juices replacing the Vitamin C solution

  6. Use a calibration curve to find the concentration of Vitamin C in each fruit juice
• Risk Assessment

  • DCPIP: Irritant to skin and eyes; may cause staining
  • Broken glass: Cuts from sharp object
  • Bags/stools: Tripping
• Daphnia ethics

  Less sophisticated nervous systems