Effect of Caffeine on Heart Rate in Daphnia

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Practical 1.1
Caffeine belongs to a class of compounds called methylxanthines and can block a receptor on the surface of heart muscle cells for adenosine. In fact, it is caffeine's blockade of the A1 adenosine receptor in the heart that causes the heart to pound after a significant caffeine dose. Caffeine and similar compounds also inhibit a class of enzymes known as cyclic nucleotide phosphodiesterases. These enzymes are, in part responsible for degrading a stimulatory signal produced when excitatory neurotransmitters activate different neurons in the central nervous system (CNS). Thus, when they are inhibited by caffeine, the stimulatory signal remains active for a longer period of time resulting in a greater sense of alertness (a CNS effect) but also a higher heart rate, blood pressure and respiratory rate. Caffeine also acts as a stimulant drug, causing increased amounts of stimulatory neurotransmitters to be released. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, causing raised stress and blood pressure. This can lead to heart and circulation problems.

Daphnia subjected to a caffeine solution will show a rise in heart rate as caffeine is a stimulant that speeds up the body affecting the nervous system and rate in which the nerve pulses are sent and received in humans. (Caffeine increases the heart rate of Daphnia. )

Null Hypothesis:
There is no significant difference between the heart rate of Daphnia in distilled water compared to that in caffeine.

Handle cavity slide carefully to prevent breakage.

Ethics for the Daphnia:
1. Every possible attempt to keep Daphnia alive.
2. Use low concentration of caffeine so not to harm the Daphnia. 3. Place the Daphnia in the presence of pond water instead of distilled water. 4. Use the same Daphnia throughout the whole experiment and handle it with care. 5. Turn off the microscope light between observations to...
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