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How does caffeine and ethanol affect the heart rate?

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How does caffeine and ethanol affect the heart rate? Introduction At rest a normal adult heart beats around 75 times per minute. During strenuous exercise it may rise to 200 beats per minute. The SAN (sino-atrial node) controls the heart rate. Information is sent via two autonomic nerves that link the SAN with cardiovascular centre in the medulla of the brain, the rate increases or decreases depending on the information received. Factors, which affect the heart: > The secretion of adrenaline. This may be under stress, excitement or other emotions. > Movement of the limbs (exercise). Heart rate and breathing rate increase due to oxygen levels falling and levels of carbon dioxide rising. > Blood pressure. When blood pressure is too high, a mechanism prevents increase in heart rate. Adrenaline is a hormone, which is produced by the adrenal gland; it is usually secreted in tiny amounts, when stressed or scared. It raises your heart rate immediately. Adrenaline improves the strength of the contractions of the heart. ...read more.


The caffeine was inserted into the cavity slide along with the daphnia using a pipette. The caffeine needed to be concentrated in order for the daphnia to survive. Again, the slide was placed under the microscope. The same process as before was carried out to record the number of beats per minute. The concentration of the caffeine used was 1x10 % = 0.00001 The exact same process was used for the ethanol experiment. However, instead of inserting caffeine into the cavity slide, after removing the water, ethanol replaced it. The ethanol also needed to be concentrated and had a concentration of 35%. A concentration of 5% was used, but this proved to be too strong for the daphnia and they died, so 35% seemed to be appropriate. Lab coats were worn throughout the experiment to ensure no substances were spilt over our clothes. After the experiment, hands were washed so that any possible contact from the water(from the daphnia)was washed. Results Original (Daphnia in water) Daphnia Number Reading One Number of beats/min Reading Two Number of beats/min Reading Three Number of beats/min 1 112 132 136 ...read more.


Ethanol: looking at the graphs we can see that ethanol has slowed down the heart rate. In figure 3, it is clear that here is where the widest difference between the original number of beats per minute and the number of beats per minute in ethanol. Crustacean heartbeats are regulated by nerve pulses. The impulses are regulated by pacemaker neurones located in a group of nerve cells called the cardiac Ganglion. Impulses are transferred to larger follower neurones, these carry signals to the cardiac muscle resulting in a heartbeat. For ethanol to decrease the heart rate, it must have some sort of effect on the nerves. When hormones attach to the receptor, the change in the nerve takes place, then the change in the heart rate. Some hormones stimulate an increase and some hormones decrease the heart rate. The nerve fibres conducting pulses to the hearts of daphnia may contain receptors that inappropriately bind to ethanol causing a decrease in the nerve activity. From the above it is possible to say that my hypothesis was correct. Caffeine, being a stimulant, increased the heart rate and ethanol, being a depressant, decreased the heart rate. Melissa Osman 5 ...read more.

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