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