Daphnia Practical

• Why is Daphnia selected as the organism in this practical?

  They have translucent bodies so the heart rate can be more easily observed.
• 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?

  Replace caffeine solution with distilled water to measure the heart rate of the Daphnia without the effect of caffeine.
• What steps should students take to ensure that the Daphnia are ethically treated?

  • Minimise the amount of time exposed to stressful testing conditions

  • Release into a stream/pond after the practical
• Why should a cover slip not be used when observing the organism?

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

  To restrict the movement of the organism so that it will be easier to count its heart rate.
• Outline the procedure to this practical.

  • Dilute the caffeine solution to produce several concentrations.
  • Place some cotton wool on a cavity slide. Add one large water flea. Use filter paper to absorb excess water.
  • Use a dropping pipette to add a few drops of distilled water to the slide.
  • Use a stopwatch to time a minute and record the number of heartbeats.
  • Repeat the experiment, replacing the distilled water with a caffeine solution.