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Does Caffeine Affect Heart Rate?

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DOES CAFFEINE AFFECT HEART RATE? AIM: We intend to investigate the effect of caffeine on the heart rate of Daphnia (water fleas). BACKGROUND INFORMATION: Daphnia's is the name of a group of small, aquatic crustaceans commonly called "Water Flea" Because their exoskeletons are clear; it is possible to watch Daphnia hearts without cutting the open. This allows the changes in Daphnia heart rate to be studied easily. The normal habitat of a Daphnia is lakes, rivers and ponds they are also used as fast food for fish. They are used as a fast food for fish because they swim fast and they make the fish fight for their food and not to just to rely on the food just coming to them. A usual life span of a Daphnia is two or three days. Daphnia's are usually females and only a few males are produced the reason for this is they are not needed as much as females are. Caffeine is widely known as a stimulant. Stimulants cause an increase in the metabolism of the human body resulting in an increase in the rate of the heart and lungs. In small doses they wake you up and give you a high by exciting the central nervous system. In high doses they can make you anxious, irritable and even psychotic. ...read more.


Adrenaline is the 'fight or flight' hormone and has a number of effects on your body. Some of the effects happen to be an in heart BPM (beats per minute), which is an increase in heart rate, and an increase in blood pressure. Just like in a human heart, a Daphnia's heart will beat faster when receiving a dose of caffeine. METHOD: A few strands of cotton wool were placed on a cavity slide (helps restrict the movement of the Daphnia). Using a pipette, one large water flea was transferred to the cavity slide. Before doing so, the water around the Daphnia was removed using a paper towel. A few drops of distilled water were added to the cavity slide containing the Daphnia. A cavity slide filled with iced water was placed under a different slide and was sealed by a cover slip (this will act as a heat sink). This slide was then placed below the slide containing the Daphnia, and was inserted under a microscope, and a lamp, which was at a reasonable distance from the microscope, was used to provide light. The built-in microscope light was not used as this would give temperature to the Daphnia and water, which could affect the results. The Daphnia was then viewed under low power, focussing on its heart, which was able to be seen through its translucent body. ...read more.


Its heart rate is measured to find out how toxic a liquid is. EVALUATION: There are many factors, which affect the results. The most obvious factor with the method used to measure the daphnia's heart rate. A daphnia's heart rate can rise to a very high rate, especially when using a stimulant such as caffeine, and thus it can be very difficult to measure using a ticker timer or even dotting on a paper. This is due to the restraints of the human reflexes; they are simply not fast enough in some cases. Another major factor is that it is feasible that a larger daphnia would not be as greatly affected by a certain concentration of caffeine as a smaller daphnia. This is because a larger daphnia would have a more diluted level of caffeine within its system. Other factors, which could affect the heart rate are, the temperature of water surrounding daphnia, the concentration of chemicals in the surrounding water (could reduce caffeine intake), amount of water surrounding daphnia, the concentration of oxygen in the surrounding water, the drops of iced water into the slide (could affect the temperature). The concentration of other gases in the surrounding water such as carbon dioxide could also affect the temperature as it can limit the amount of oxygen in the surroundings. The caffeine solution used could not have been fully mixed in with the water; therefore the concentration taken could not have been what it was actually planned to be. Tahamtan Pishgharavol Biology ...read more.

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This is a well researched report that covers the necessary aspects.
1. The introduction should be referenced.
2. The method should be in numbered steps.
3. The conclusion is well detailed.
4. The evaluation shows a good understanding of scientific processes.

Marked by teacher Luke Smithen 05/07/2013

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