Concentration of caffein


The effect of the concentration of caffeine on the heart rate


To investigate the effect of the concentration of caffeine on the living thing's heart rate (Daphnia)


[1]Heart rate can be defined as the number of heart beats per unit time, usually per minute. The heart rate is based on the number of contractions of the ventricles (the lower chambers of the heart). The heart rate may be too fast (tachycardia) or too slow (bradycardia). The pulse is bulge of an artery from the wave of blood coursing through the blood vessel as a result of the heart beat. The pulse is often taken at the wrist to estimate the heart rate. Heart rate, which defines the number of contractions of the human heart in one minute, at rest for the male adult human heart, beats approximately 70 beats per minute; whereas, female hearts tend to beat faster at around 75 beats per minute. There's physical exercise causes a normal person's heart rate to increase above the resting heart rate; as the physical activity becomes more vigorous, the heart rate increases, reaching maximum heart rate with very vigorous exercise.

However, there's still factor that lead to increase and decrease of the heart rate of human or even the animal. There are a number of different factors that affect the control and response of heart rate. Heart rate is affected by external stresses on the body such as heat, humidity, cold, wind, and altitude and air quality. With each stress, the human heart is affected and different compensatory changes occur, one of those being adjustment in the beat of the heart. Triathletes racing at the Hawaiian Ironman face most of these conditions simultaneously while racing in one of the most strenuous events in the world. As a result, a heart rate monitor can help provide them with key information on how their body is responding to the conditions and the duration of this high intensity racing throughout the event. Almost any substance taken into the body affects the equilibrium of the organism. Heart rate is one of the quickest changes that occur as a direct reflection of this change that results in disequilibrium.

[2]For example, beta blockers (Inderal, Propranolol, Lopressor, etc.) cause bradycardia or the heart rate to drop. Similarly, the antiarrhythmic agents (Cardioquin, Procaine, Quinidine, etc.) given to patients to improve cardiac function also causes a decrease in heart rate. Pulmonary bronchodilator drugs such as the sympathomimetics (Isoproterenol, Ephedrine, Bronkosol, etc.) because of tachycardia or increase in heart rate values. Drugs that act as stimulants such as caffeine, nicotine, methamphetamines and cocaine cause tachycardia and drugs that are depressants, barbiturates, tranquilizers, alcohol and Quaaludes cause bradycardia. Some drugs like inhalants can cause either a quickening or depressing of heart rate and respiration. Other changes can cause changes in heart rate are lack of sleep, irritability, rapid changes in blood chemistry such as blood sugar levels, reactions to different types of ingested foods can both lower and raise resting and exercising heart rates. Emotions play a large role in heart rate response. Anger, fear, and anxiety cause tachycardia while depression usually results in lowering of heart rate. Feelings of love, compassion, happiness usually result in bradycardia. Emotional stress causes heart rate to stay elevated.

There is a moderate increase in heart size and anatomies regardless of age as the result of an aerobic and anaerobic training program. Some of the changes that happen to the fit, athletic heart muscles are improved cardiac output, lower resting and ambient heart rates, increased stroke volume, enlarged ventricular chamber, thickening of the heart walls, improved coronary blood flow, and improved mitochondria mass Increase number of respiratory enzymes in the myocardium. The genes that you inherited are responsible for much in our lives. They too affect heart rates. It appears that the effect of your genetic makeup accounts for about 50% of the value of your maximum heart rate. This means that if your parents both have a low maximum heart rate, the odds are favourable that you will as well. High amounts of caffeine can have a negative effect upon health partly due to caffeine's huge role in alertness, because sleep is often altered by high doses of caffeine in one's system.

The high dosage of caffeine led to reduced total sleep time and more restlessness. That the caffeine did not have as much of an effect on the habitual caffeine users as the other subjects means that most likely, people who habitually consume caffeine are not susceptible to lasting effects once they have slept. Overall, however, caffeine was concluded to have exerted mild harmful effects on recovery sleep when following total sleep deprivation. These effects usually take place in the early sleep period and can be recovered from by sufficient sleep. This remedy of caffeine-affected sleep was shown by the lack of post-recovery sleep performance deficits. Habitual caffeine use was also affirmatively concluded to reduce the effects of caffeine, even if only minimally. As commonly known, caffeine is a stimulant that affects the central nervous system, metabolism, and cardiovascular functions of the body. Stimulants are substances that, among other things, cause an increased heart rate. When stimulants are abused, the resultant heart rate increase can be dangerous or even fatal. Some stimulants are prescribed for various medical conditions and can be administered in some cases of cardiac arrest to restart the heartbeat; however, stimulants may also cause heart trauma such as cardiac arrest. Stimulants are psychoactive substances that create an effect by increasing levels of dopamine in the brain. Dopamine is a neurotransmitter that regulates pleasure, movement and attention.

Common legal drugs such as caffeine and nicotine are stimulants, as are a variety of over-the-counter medications. Other stimulants are controlled substances available by prescription for the treatment of obesity, narcolepsy and attention deficit disorder. Drugs of abuse, such as cocaine and methamphetamine, are stimulants as well. Stimulants increase blood pressure and heart rate. They also increase respiration, body temperature and mental activity. Stimulants constrict blood vessels and increase blood glucose levels. They can diminish the appetite and increase alertness, energy and wakefulness. Stimulants, and particularly those that are drugs of abuse, such as cocaine and methamphetamine, can produce negative side effects. A 1997 study by the National Addiction Centre in London reported that anxiety, depression, paranoia, panic attacks and sleep disturbances can be attributed to stimulant abuse. At high doses, and for those with pre-existing heart conditions, stimulants can raise the heart rate to a dangerous level, producing heart attacks, heart failure, seizures and strokes. The combined use of stimulants and certain over-the-counter decongestants can raise the blood pressure to an unhealthy degree and cause an irregular heartbeat.

[3]Caffeine is medically known as trimethylzanthine. Its chemical formula is C8H10N4O2. When in pure form, caffeine is white crystalline powders that taste very bitter. The most common way of acquiring pure caffeine is the process of decaffeinating coffee and tea. Caffeine is useful as a cardiac stimulant and also as a mild diuretic. Cardiac stimulants increase the heart rate, and diuretics increase urine production. Caffeine is also used to provide a “boost of energy” or a feeling of heightened alertness. Caffeine is also an addictive drug. It operates using the same mechanisms that amphetamines, cocaine and heroin use to stimulate the brain. Caffeine's effects are milder than the above listed drugs, but it is manipulating the same channels and this gives caffeine its addictive qualities. If you feel like you cannot function without it, then you are addicted to caffeine. These days caffeine is also used as a flavour enhancer in a wide range of cola and other soft drinks. In addition, it has medicinal uses in aspirin preparations and is found in weight-loss drugs and as a stimulant in students' exam-time favourites like Pro-plus and Red Bull. In humans, caffeine is a central nervous system (CNS) stimulant, having the effect of temporarily warding off drowsiness and restoring alertness. Beverages containing caffeine, such as coffee, tea, soft drinks and energy drinks enjoy great popularity.

Caffeine occurs naturally in many plants, such as, coffee beans, tea leaves and cocoa nuts. Caffeine is added artificially to many products, including a variety of beverages. There are steps that could explain the way of caffeine work. First as our brain creates a chemical called Adenosine, this chemical binds to adenosine receptors in the brain. The binding of adenosine causes drowsiness by slowing down nerve cell activity. To a nerve cell, caffeine looks like adenosine, and caffeine binds to the adenosine receptors. The caffeine does not slow down the cell's activity like adenosine, but instead, speeds up the cell's activities. Caffeine also constricts the brain's blood vessels. If you have a vascular headache, caffeine can slow down the blood flow to the brain and relieve it.

Therefore, some headache medicines like Anacine contain caffeine. The pituitary gland sees all of the activity and thinks some sort of emergency must be occurring and causes a release of the hormone Adrenaline. Adrenaline speeds up the bodies functions even 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. If a person drinks a big cup of coffee with 200 mg of caffeine in it at 3:00 PM, about 100mg is still in that particular person's system at 9:00 PM. He/she may be able to fall asleep, but his/her body probably will miss out on the benefits of deep sleep. The deficit adds up fast. The next day those people will feel worse and need caffeine as soon as get out of bed. The cycle continues day after day. However, everyone should notice that heart rate is not affected by body composition. It's not affected by body type. It is affected by heart size with smaller hearts typically having higher resting and ambient heart rates. At high levels of consumption caffeine has been linked to restlessness, insomnia and anxiety, causing raised stress and blood pressure. This can lead to heart and circulation problems. Caffeine has a very obvious effect upon the daphnia's heart rate. To determine the effects of caffeine in human life we have to take a substitute of a human being and then infer that any result that we obtain from this experiment will be the same as what will happen in a human. Obviously we have to take into account that the amount of caffeine consumption of the daphnia and that of a human will be different as the scales as to how big we are a different.

[4]Daphnia are small freshwater crustaceans that may also be known as water fleas. They are called this because of their short jerky hopping movement through the water. There are many species of Daphniidae and their distribution is worldwide. Of all the species, the genera of Daphnia and Moina are the most diverse, and are a major food source for both young and adult freshwater fish. In the orient, Moina is the species of Daphniidae most used in fish culture. The daphnia has both sexual and asexual phases.

In most environments, the population consists entirely of females that reproduce asexually. Under optimum conditions, a female may produce more than 100 eggs per brood, repeating every 3 days. A female may have as many as 25 broods in its lifetime, but the average is about 6. The female will start to reproduce at about 4 days old with a brood size of 4 to 22 eggs. Under adverse conditions, males are produced, and sexual reproduction begins. The result is the laying of resting eggs, just like the brine shrimp. Factors that can trigger this are a lack of food, low oxygen supply, a high population density, or low temperatures.

Daphnia are generally tolerant of poor water quality, and dissolved oxygen varies from almost zero to super saturation. Like the Brine Shrimp, their ability to survive in an oxygen poor environment is in their ability to synthesize haemoglobin. The production of haemoglobin may be promoted by high temperatures, and a high population. Also, like brine shrimp, Daphnia are not tolerant of fine air bubbles. A slow aeration is needed with Daphnia as a large bubble column will strip the Daphnia out and kill them. A pH between 6.5 and 9.5 is acceptable for them to leave. High ammonia levels, with high pH will drastically reduce reproduction, but will not affect the actual health of the animals themselves. So it seems that on the small scale that we require, monitoring of pH and ammonia is not critical to success.

In contrast to their tolerance of low oxygen, Daphnia are very sensitive to disturbances of the ionic composition of their environment. They become immobile and eventually die with the addition of salts like sodium, potassium, magnesium, and calcium. Daphnia are not affected by the addition of nitrogen in fertilizers for the promotion of algae growth. Daphnia have a wide tolerance to temperature. The optimum temperature for Daphnia Magna is 18-22 ⁰C (64-72 F). Daphnia feed on various groups of bacteria, yeast, microalgae, detritus, and dissolved organic matter. Bacterial and fungal cells are high in food value, but all foods rank second to microalgae. A good algae culture is vital to growing these guys, so if you set out to do everything you can to growing a flourishing algae culture you will be ensured success.

Problem statement:

How does the concentration of the caffeine affect the heart rate?


The Daphnia which is subjected to a caffeine solution will show a rise in heart rate, this rise in heart rate should reflect the concentration of caffeine in a given solution. As caffeine is a stimulant that speeds up the body affecting the nervous system and heart rate in which the nerve pulses are sent and received in humans. So I believe the usage of caffeine on the daphnia will increase its heart rate linearly with the increase of concentration of caffeine.

Variable: (a) Fixed variable : Type daphnia used

(b) Manipulated variable : Concentration of caffeine (mg/ml)

(c) Responding variable : Heartbeats produced per minute (minˉ¹)

Materials : Culture of Daphnia (water fleas), distilled water or pond water, caffeine solution

Apparatus: Cavity slides, Pasteur pipettes, muslin cloths, standard glassware (beakers, measuring cylinders etc), stopclock, paper towels, and microscope


1. Set up the microscope first and gathered all the equipment. Prepared the caffeine concentration by weighing up the caffeine solute based on the required concentration and 100ml of water is added up till they reached concentration of 0.1mg/ml, 0.2mg/ml, 0.3mg/ml, 0.4mg/ml and 0.5mg/ml.

2. Took out a daphnia from its place by using the dropper. Suck it slowly. Then sucked daphnia is put on the cavity slide which is right on the centre.

3. Water origin from its pond is dropped approximately covered its body.

4. Then, muslin cloth is put on top of daphnia's body evenly and enough to make it stationary and next placed it under the microscope.

5. Adjust the lens from coarse to smooth power till the image of daphnia's heart can be seen clearly it's pumping.

6. After finished adjusting the lens, start count the pulse of the daphnia over 15 seconds using the stopclock, this step is repeated three times to achieve the average range of each its heartbeat over particular caffeine concentration.

7. First counting process is done with the 0 mg/ml concentration of caffeine which acts as control result.

8. Then the counting process of heartbeats is followed with the lowest concentration of caffeine which is 0.1 mg/ml and before started counting left the daphnia for a while to adjust itself with the solution.

9. Next, the concentration of caffeine is added gradually on the daphnia which are 0.2mg/ml, 0.3mg/ml, 0.4mg/ml and the highest concentration of 0.5 mg/ml.

10. The daphnia is put onto the glass bowl back after finished the experiment.

11. Repeat step 10 each by three times.

12. Result is tabulated in table below.

Result: Table of concentration of caffeine prepared (mg/ml) and the heartbeats produced in one minute (minˉ¹)

Concentration of caffeine (mg/ml)

Heartbeats per minute (minˉ¹)





































The graph of heartbeats produced per minute (minˉ¹) against the concentration of the caffeine (mg/ml)



Caffeine has a very obvious effect upon the daphnia's heartbeats. In each experiment of different caffeine concentration, the daphnia were observed to be very jumpy, excitable, and active after exposure to the caffeine. Their heart rates almost always increased, and in some situations doubled. This supports the present knowledge that states that caffeine increases heartbeats. To measure the heart rate of a daphnia, one daphnia was extracted from the glass bowl using a dropper, and placed on a slide. As much water as possible was taken up while one drop of each 0.1mg/ml, 0.2mg/ml, 0.3mg/ml, 0.4mg/ml and 0.5mg/ml concentration of caffeine was put on top of the daphnia. The number of beats was counted while running the timer. This was repeated with three times by using same daphnia. Once these three were measured, the daphnia were placed back into its place with the others. The control result here is the non-concentrated of the caffeine, which is 0 mg/ml. This indicates that the normal heartbeats of the daphnia without any others solution.

Referred to the graph plotted, it is clearly shown that whenever there is an increase in the concentration of caffeine the heartbeats of daphnia will raise per minute. But then, this pattern seems like disobeyed the theory when it comes to the concentration of 0.5mg/ml, the highest caffeine contained. The manipulated variable of concentration of caffeine obviously affects the way of daphnia's heartbeats. The highest concentration of caffeine which is 0.5mg/ml tends to lower the daphnia heartbeat. This can be laid on the reason that of individual daphnia has different level of active. There's daphnia that very active towards the external disturbance which is in this case is the caffeine solution. Our group who's carried out the concentration of 0.5mg/ml caffeine might be used the passive type of daphnia. That is why our result does not reflect with the theory of stimulant is factor of increase in heartbeats. This is the limitation in this experiment.

Another limitation is the apparatus used which can affect the concentration of caffeine produced. Our group used the measuring cylinder to make the 0.5mg/ml concentration, this measuring cylinder actually made the solution more dilute compared to the other groups who used beaker to mix up the caffeine. Beaker will make solution more concentrated as their scale measurement is small than measuring cylinder. The purpose of using the muslin cloth on top of daphnia is to restrict the movement of daphnia in order to observe it clearly and make it easier to count the heartbeats. During the gap to add another concentration of caffeine, give the daphnia the supplement of oxygen by dropping some water. Use pond water/Daphnia culture solution for both the control group and to dissolve the caffeine as this may give more valid results and be less stressful to the Daphnia. In distilled water the heart rate may rise due to lack of oxygen.

By relating Daphnia results to data for human responses to caffeine, there are many difficulties in making comparisons between data collected from these both different species, human and daphnia. For example, to account for differences in metabolism, and the vastly different body size, these can be considered as difficulties as human scale is varied and large. The pH level could also be a factor in final results. As we all know the water of the pond is actually could also contain the pollutant, these pollutant sometimes has theirs pH whether high or low. A stronger or weaker pH of the water could have caused a change in heart rate for the daphnia as opposed to a neutral pH. Also, it might have helped if the sample size was larger in order to get results that were not as limited. The net conclusion that can be drawn is that caffeine did lower heart rate in the species known as Daphnia magna. This conclusion does not support the original research hypothesis, which stated that, if a given amount of caffeine is administered to a group of daphnia, then the heart rate will speed up abnormally. It does, however, support the statistical alternate hypothesis, which stated that the number of heart beats before the caffeine was administered is not equal to the number of heart beats after the caffeine was administered.

Safety precaution:

Wear the lab coat as protection as if the caffeine solution spilled over. Take care with the glassware make sure that they do not break. The microscopes are fragile and the light bulbs can get hot so be careful of that. Make sure to keep your area neat and organized and if you spill the caffeine solution, cleaning it up to avoid spilled area becomes sticky. Carefully during took out the daphnia from the glass beaker using the dropper, make sure the hole of dropper placed exactly on daphnia's body. Noticed that high concentration of caffeine can be fatal for the daphnia, so whenever put those concentrated caffeine on the daphnia ensure that it is dropped slowly. Put the muslin cloth exactly on its body to restrict its movement.

Improvement and suggestion:

The Daphnia hearts are fairly easily seen but counting the number of beats can be difficult. Counting is easier if each heartbeat is recorded by tapping a pencil on a piece of paper and counting up the pencil marks after the specified time. In addition, cooling the Daphnia before the experiment may help slow their heart rate. Use of the stroboscope may overcome the problems of counting faster heart rates. A simpler approach is to count the rate at which the legs beat. This rate is proportional to the rate at which the heartbeats. To prevent the Daphnia from overheating while on the microscope turn off the microscope light between observations and use a heat sink; a cavity tile filled with iced water placed on the microscope under the slide.


It's shown that the amount of caffeine in the blood will determine the heart rate of the daphnia. It will be directly proportional to each other so the increase of the concentration of caffeine will also increase the heart rate. Hypothesis is accepted.






5. Edexcel Biology for AS, C J Clegg, Hodder Education





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