Aim: The aim of this investigation is to investigate the affect of caffeine on the heart rate of Daphnia (Water Fleas).
Hypothesis: The heart rate of the Daphnia will increase when exposed to caffeine. Caffeine acts as a stimulant, which causes stimulatory neurotransmitters to be released in excess amounts. This makes the brain feel more alert and also increases mental activity. Therefore an increase in the heart rate is likely if more physical activity is taking place.
1. Set up apparatus needed- 6 Daphnia, cavity slides, dropping pipettes, distilled water, caffeine tablets, cotton wool, glass beakers, test tubes, test tube rack, stop clock, filter paper, and microscope.
2. After equipment is set us, collect 6 Daphnia. Place 3 into pond water and 3 into caffeine solution.
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.