daphnia experiment

• daphnia also known as water fleas are small aquatic invertebrates
• daphnia are suitable for investigating heart rate due to having transparent bodies; their internal organs, such as the heart, can be observed using a light microscope
• caffeine is a stimulant which increases heart rate by increasing release of excitatory neurotransmitters
• IV: caffeine concentration

  DV: heart rate of daphnia (bpm)
• temp should be controlled

  • to prevent fluctuations that could affect daphnia's metabolic and heart rates
• volume of caffeine should be controlled

  • to ensure uniform concentration and reliable results
• stress of daphnia should be controlled:

  • minimise stress factors like handling and crowding to avoid confounding effects on experimental outcomes
• size of daphnia should be controlled:

  • to reduce variability and ensure observed effects are not due to size differences
• control time to acclimatise:

  • allow daphnia time to adjust to experimental conditions to stabilise psychological processes and minimise stress before the experiment begins
• method

  1. prepare 5 different conc. of caffeine solution and control solution of distilled water
  2. add some pond water into the well of a cavity slide and add 3 drops of distilled water
  3. select a large daphnia and use a pipette to transfer it to the cavity slide
• method pt 2

  4. observe the animal under a microscope

  5. use a stopwatch to time 20 seconds and count number of heartbeats by making dots on a piece of paper

  6. count the dots and express heart rate as number of beats per minute, multiply by 3 to convert beats per 20 seconds into beats per 60 seconds
• method pt 3

  7. return daphnia to the stock culture

  8. repeat steps 3-7 with at least 5 other daphnia individuals

  9. repeat steps 3-8 with different caffeine concentration solutions
• conclusion: caffeine increases the heart rate of daphnia by increasing the release of stimulatory neurotransmitters. as concentration of caffeine increases, heart rate also increases
• we can minimise suffering of daphnia by:

  • returning daphnia to natural habitat after use
  • storing daphnia in conditions that replicate natural environment
  • working at a good pace to minimise time daphnia are under any stress
  • turning off microscope lamp when not in use, daphnia are cold-blooded
  • not using an excessive amount/conc. of caffeine
• we use daphnia because

  • they are common, there is no real threat to species' existence or its dependent species
  • no threat to daphnia reproduction because they reproduce asexually - no loss of genetic variation
  • possess a less developed nervous system, therefore reduced awareness of pain