CP1: effect of caffeine on heart rate

• What is the independent variable (variable being changed)?

  The concentration of caffeine in solution Daphnia are being exposed to
• What is the dependent variable? (variable being measured)

  -The heart rate of Daphnia (measured in bpm)
• What are the control variables? (variables being kept the same)

  -volume of caffeine solution

  -temperature of environment/surroundings

  -size, age, gender of Daphnia

  -time given to acclimatise

  -time the heartbeat is measured for
• What apparatus is used?

  -light microscope

  -petri dish

  -pipette

  -culture of Daphnia

  -stopwatch

  -distilled water

  -various concentrations of caffeine solutions

  -graph paper
• how to control volume of caffeine solution

  pipette to ensure consistent volume ( prevents inconsistency in exposure levels )
• how to control temperature and why as a control variable

  conduct in room temp, use thermometer to regulate temp ( temp could alter heart rate )
• how to control type / size of daphnia

  use same gender from same culture same size ( standardises baseline conditions of investigation )
• how to control time to acclimatise

  stopwatch - ensures same effect of caffeine on each daphnia
• how to control time measured of heartbeat

  stop watch - increases validity
• procedure step 1


  add pond water small amount into well of cavity or petri dish + small amount of disitilled water to prevent dessication and maintain hydration
• procedure step 2


  select large daphnia using pipette and place in pond water and then under microscope
• procedure step 3


  measure heart rate for 20 seconds and x3 for one minute
• procedure step 4


  repeat step 1-3 with 5 other Daphnia individuals for each caffeine concentration and for control use distilled water