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

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Activity 1.21 Does Caffeine Affect the Heart Rate? 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. Method: 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. ...read more.


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. ...read more.


* 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 ...read more.

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