Caffeine is an addictive drug. Among its many actions, it operates using the same mechanisms that amphetamines, cocaine, and heroin use to stimulate the brain.
Caffeine works by changing the chemistry of the brain. It blocks the action of a natural brain chemical that is associated with sleep.
As adenosine is created in the brain, it binds to adenosine receptors. The binding of adenosine causes drowsiness by slowing down nerve cell activity. In the brain, adenosine binding also causes blood vessels to dilate (presumably to let more oxygen in during sleep).
To a nerve cell, caffeine looks like adenosine. Caffeine therefore binds to the adenosine receptor. However, it doesn’t slow down the cell’s activity like adenosine would. The cells cannot “see” adenosine anymore because caffeine is taking up all the receptors adenosine binds to. So instead of slowing down because of the adenosine level, the cells speed up. You can see that caffeine also causes the brain’s blood vessels to constrict, because it blocks adenosine’s ability to open them up. This effect is why some headache medicines like Anacin contain caffeine.
So now you have increased neuron firing in the brain. The pituitary gland sees all of the activity and thinks some sort of emergency must be occurring, so it releases hormones that tell the adrenal glands to produce adrenaline.
Caffeine also increases dopamine levels in the same way that amphetamines do (heroine and cocaine also manipulate dopamine levels by slowing down the rate of dopamine re-uptake). Dopamine is a neurotransmitter that, in certain parts of the brain, activates the pleasure centre. Obviously, caffeine’s effect is much lower than heroine’s, but it is the same mechanism. It is suspected that the dopamine connection contributes to caffeine addiction.
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:
- Measure resting pulse.
- Measure out 70ml of coke, and drink it.
- Take your pulse immediately after drinking.
- Take your pulse every minute until it goes back to normal.
- Repeat above with 70ml of coffee.
- 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. The intervals between which I take my pulse must also stay the same.
My pulse rate is the key factor in this experiment; it will increase due to the caffeine in the drinks, because caffeine causes the heart to beat faster. The more caffeine in the drink, the more my pulse rate will increase.
Fair test:
To make this experiment fair, I will be sitting during the whole experiment, to limit the change in my pulse. Beforehand, I will not drink anything with caffeine in it, or take part in energetic exercise, because this could affect my pulse rate. I will also try to keep my resting pulse the same before each experiment, and the time intervals between measuring my pulse must also be kept the same.
Measuring:
Volume of drink- 70ml (water and coffee powder)- measuring cylinder
Pulse rate- B.P.M.- stop clock and pulse reader
Time in between taking pulse rate- minutes- stop clock.
Safety:
I must be careful with hot water, and don’t drink too much. I will also be aware of the dangers of drinking in a laboratory.
Results:
Averages: (B.P.M.)
Coke- starting= 56 Caffeine- starting= 56
0= 69 0= 63
1= 71 1= 67
2= 62 2= 57
3= 53 3= 50
Conclusion:
My graph clearly shows an increase in my pulse rate. My pulse increases straight after drinking, and then carries on increasing for another minute, before decreasing more gradually. This is because the caffeine had an immediate effect on my pulse, but it didn’t stop immediately. The pattern of results is good, and it is clear what my results show.
I conclude that caffeine does have an effect on my pulse rate. My experiment showed that coke increased my pulse rate more than coffee. My prediction was incorrect. This was because I predicted that coffee would increase my pulse more than coke, because it contains more caffeine, so I thought it would stimulate my heart 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.
