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Investigation into the effects of caffeine on pulse rate.

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Investigation into the effects of caffeine on pulse rate Introduction: I am going to do an experiment to see how caffeine affects my pulse rate. I will drink coffee and coke, and compare how much my pulse increases when each drink is consumed. Background knowledge: Caffeine is classed as a central nervous system stimulant. Stimulants affect the brain by either increasing or decreasing its activity. It is thought that they work on the synapses in the brain. There are millions of nerve fibres in the brain, and millions of connections between them, called synapses. Nerve impulses cross synapses by messenger molecules. Caffeine is a stimulant because they cause the release of more messenger molecules than normal. In moderate doses, caffeine can: increase alertness, reduce fine motor co-ordination, alter sleep patterns, and cause serious headaches, nervousness and dizziness. In massive doses caffeine is lethal. Caffeine enters the bloodstream through the stomach and small intestine, and can have its effects as soon as 15 minutes after it has been consumed. Once in the body, caffeine will stay around for hours- it takes up to 6 hours for one half of the caffeine to be eliminated. Caffeine belongs to the xanthine chemical group. Adenosine is a naturally occurring xanthine in the brain that is used as a neurotransmitter at some synapses. One effect of caffeine is to interfere with adenosine at multiple sites in the brain including the reticular formation. ...read more.


The most important long-term problem is the effect that caffeine has on sleep. Adenosine reception is important to sleep, and especially to deep sleep. The half-life of caffeine in the body is about 6 hours. That means if you consume a big cup of coffee with 200mg of caffeine in it at 3:00 pm, by 9:00pm about 100mg of that caffeine is still in your system. You may be able to fall asleep, but your body probably will miss out on the benefits of deep sleep. That deficit adds up fast. Prediction: I think that drinking coffee will increase my pulse rate more than drinking coke because it contains more caffeine (50-100mg compared to 20mg in coke). It will increase my pulse because caffeine is a stimulant and it causes your heart to beat faster. Equipment: Coke, Coffee, Water, Kettle, Sterile measuring cylinder (Sugar, milk) Cup, Spoon, Stop clock. Diagram: Method: 1) Measure resting pulse. 2) Measure out 70ml of coke, and drink it. 3) Take your pulse immediately after drinking. 4) Take your pulse every minute until it goes back to normal. 5) Repeat above with 70ml of coffee. 6) Repeat all of the above twice. Key factors: In this investigation I will change what I am drinking. Drinks with more caffeine will increase my pulse rate more. The volume of drink must be kept the same throughout the experiment, as well as my starting pulse rate. ...read more.


To test whether this would happen again, I would need to repeat the experiment, under the same conditions, and compare my results. Evaluation: I think that my results are quite reliable, as I repeated the experiment three times. Most of the evidence I have collected is valid, but my pulse could have been affected as I conducted the experiment on two separate days, at different times during the day. There isn't a vast amount of difference between my pulse when coffee and coke were drank, but I didn't expect coke to increase my pulse rate more, as it contains less caffeine. My measurements were accurate, so I drank the same amount of liquid each time. I don't normally drink coffee, and I don't drink much coke, so I don't think this would have affected my experiment. As I drank three lots of coke first, then coffee, it may be possible that by the time I drank coffee my body had got used to the caffeine. I am not very confident about my results, I would have to repeat the experiment to see if the same happened again. If I were to conduct this experiment again I would alternate what I drank to see if that affected my results, and try to collect all of my evidence on one day, because then the circumstances around me would be the same throughout the experiment. ...read more.

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