Caffeine is produced by plants as an insecticide. It is a drug that acts as a stimulant in humans and causes a raised heart rate, and is used to give more energy in drinks such as tea and coffee, add flavour to drinks such as coke, and in weight-loss foods. A raised heart rate increases the risk of cardiovascular disease as it makes the heart work faster which can wear it out. High levels of caffeine have been linked to increased stress and insomnia, which is also linked to heart disease as it raises blood pressure.
Water fleas are small crustaceans whose body is enclosed in a soft shell. They were useful in this experiment because, when looked at under a microscope, you can see their hearts beating.
My hypothesis for this experiment is that the higher the levels of caffeine the water flea was exposed to, the quicker the heart rate would be.
1. Put one water flea in a cavity slide and used filter paper to remove the excess water.
2. Add a drop of the caffeine concentration the flea will be tested with.
3. Leave the flea for 3 minutes.
4. Put the slide under the microscope and focus it so that you can clearly see the individual heartbeats.
5. Count the number of heartbeats in 15 seconds by tapping a pencil on a piece of paper.
6. Count the marks and multiply by four, to find the heartbeats per minute.
7. Put the flea in a flask of pure water.
8. Repeat with a different flea, until you have all the data you need.
Health and Safety:
During this experiment it was important to try as much as possible not to harm the fleas. They were likely to be stressed, as they were having different things done to them, so I put a little ice in their water to cool them down and keep them at a comfortable temperature.
Water fleas must be placed in pure water or in pond water, so I kept them in pure water, as they would die in tap water. The concentrations of caffeine I used were not high enough to harm them.
I kept the flea under the microscope for as little time as possible as they would get very hot under it and would not be comfortable. I also did not put a cover slip on top of the slide as it could have squashed and killed the flea.
Caffeine is not harmful so I did not wear goggles but I did wear a lab coat to protect my clothes if I spilt anything.