The aim of this investigation is to investigate the affect of caffeine on the heart rate of Daphnia (Water Fleas).

3. Then place a thin layer of cotton wool onto the slides under the microscope.

4. Collect one Daphnia from the pond water, using the pipette and place onto cotton wool. Looking under the microscope, time its heartbeat for 15 seconds using a stop clock and record.

5. Wait for 2 minutes and then record the heartbeat again for 15 seconds. Ensure the stop clock is running continuously throughout.

6. Record the heartbeat of the Daphnia every 2 minutes for 15 seconds until you have recordings for the start, after 2 mins, 4 mins and 6 mins.

7. Repeat steps 4-6 another 2 times. This will ensure the results are reliable as the experiment would have been repeated several times.

8. After having repeated the experiment, change the cotton wool and repeat steps 4-7, this time using the Daphnia from the caffeine solution.

Risk Assessment/ Safety: Wear gloves when working with biological specimen and ensure you wash hands after the practical as they may contain bacteria which could spread causing harm to others. Also make sure you wear lab coats in case of any spillage onto your clothes. Use goggles again to protect eyes, in case of spillage. Also wipe down surfaces and wash hands with anti- bacterial sprays/ soap to clean away any bacteria.

Ethical Issues: Try to ensure that the Daphnia stay alive after use as they are living creatures too. To ensure the Daphnia stay alive, use pipettes when transferring the Daphnia from the solution, to the microscope and back into pond water.

Table of Results:

Caffeine (%)

Heart Rate-

Number Of

Beats in 15

Seconds

Concentration

Time 0

2 mins

4 mins

6 mins

Mean

B/Min

33

43

42

59

//44

77

0 2

51

52

51

04

//65

258

3

86

71

89

90

84

336

Average B/M

//57

//55

//61

//84

Av. B/M

257

81

65

60

68

//69

274

0.5 2

54

50

42

43

//47

89

3

36

33

34

37

35

40

Average B/M

//57

//49

//45

//49

Av. B/M

201

Graph:

Evaluation:

There were many negative points in this investigation.

* The heartbeat of the Daphnia was too fast therefore it was easy to miss out on some beats, or count a few beats extra. This made the results unreliable.

* The Daphnia were changed for each time the experiment was repeated; therefore you don't get the average beats for the same insect, again making the test unfair.

* Amount of caffeine solution used was not consistent so heart rate would vary slightly.

* Size of Daphnia was not consistent therefore they may have reacted in different ways to the caffeine.

* The time under the microscope varied slightly.

* The cotton wool should have been changed for each experiment as it would have excessive solution, therefore making the Daphnia react differently.

Conclusion: The results show that the heart rate decreased when the Daphnia were exposed to caffeine, which was the opposite of what should have happened.

It proved the hypothesis wrong because the prediction made stated that as the concentration of caffeine increased, the heart rate of the Daphnia would also increase, but shown in the results, as the concentration increased, the Daphnia's heart rate decreased.

Zoya Khan Biology Investigation- Marcia Johnson 30-10-2006