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What is the independent variable?
What is the dependent variable?
The heart rate of the Daphina
What variable need to be controlled? ( 5 marks)
- Volume of solutions
- Stress of Daphnia
- Size of Daphnia
- Time of acclimatisation
Describe an the Daphina experiment? ( 8 marks)
- Prepare different ranges of concentration of caffeine solution of equal volume
- Using a pipette, remove one Daphina from pond water and place it on a cavity slide with cotton wool on it to stop it moving off the slide.
- Leave the Daphina on the slide for 5 minutes to allow it to acclimatise.
- Using another pippette extract a a certain amount of your solution into it and then place a small drop of the caffeine solution on the Daphina
- Then place the cavity slide under the light microscope and focus it on the beating heart of the Daphina
- Start the stopwatch and then count the number of heartbeats for 30 seconds by drawing dots on a piece of paper when a heartbeat is seen or video recording the event then multiply this value by two to find the heart beat per minute.
- Repeat the experiment again with the same concentration 2 more time using a different Daphina each time.
- Then repeat the experiment using different concentrations of caffeine solution repeating the experiment at each concentration 3 times.
What factors can affect the result of the Daphina investigation?( 3 marks)
- Ensuring Daphnia were same size
- Ensuring enough data is collected
- Counting of heart beat can be inaccurate due to human error
- If left too long under microscope, tempincreases (due to lamp) = increased heart rate
What ethical factors are there in the Daphina investigation? (2 marks)
- Too high concentration of caffeine kills
- Daphina cant give consent to partake in the test and may feel pain
Why is a Daphina used ( 4marks)
- They are invertebrates
- So are simpler organism
- they have a less sophisticated nervous system so may feel less or no pain.
- Invertebrates are more distantly related to human than other vertebrates