Daphnia Practical

Cards (7)

  • 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.