RP 1: Effect of Caffeine on Heart Rate

• Why are Daphnia an ideal organism for this practical?

  They have translucent bodies so their hearts can be easily observed/ they have no nervous system.
• How does caffeine act in humans?

  It is a stimulant that increases heart rate by increasing the release of excitatory neurotransmitters.
• How is the control set up? (Daphnia)

  Replace caffeine solution with distilled water to measure the heart rate of the daphnia without the caffeine.
• What steps must be taken to ensure the Daphnia are ethically treated?

  • Minimise the amount of time exposed to stressful testing conditions.
  • Release into a stream/pond/natural form of water following the experiment.
• Why should a cover slip not be used when observing the Daphnia?

  To allow oxygen to reach the organism, preventing conditions from becoming anoxic.
• What is the purpose of placing cotton wool near the Daphnia?

  To restrict movement of the organism to make it easier to count the heart rate.
• Outline the Practical Procedure (RP 1)

  1. Use a dilution table to make multiple caffeine concentrations.
  2. Place some cotton wool strands on a cavity slide. Add one large daphnia and use filter paper to absorb excess water.
  3. Use a dropping pipette to add some distilled water to the slide.
  4. Use a stopwatch to time 20 seconds and record heart rate.
  5. Multiply to find beats per minute.
  6. Repeat with other caffeine concentrations and compare heart rates.