How caffeine affects the heart rate – experiment

using

Daphnia

What are Daphnia, and why are they used?

- Daphnia, also commonly known as water fleas, are

small crustaceans that live in lakes, ponds, streams - or most fresh water.

- They serve as an important part of the food chain, as

food to fresh water fish and other organisms living in these fresh water conditions.

- They are 1-5 millimetres long with a translucent ex-

oskeleton, that is split up into segments. Their heart rate is approximately 180 bpm.

- Their heart is located behind the head, at the top of

their back, which means it is easy to identify. The heart beat can be clearly observed through a tele-scope and so Daphnia are used to observe the effect of caffeine.

- Their small bodies mean that caffeine quickly diffuses

into their blood stream, causing a very quick change in heart rate.

- Daphnia can be easily raised and kept in an aquarium

How does caffeine affect the heart?

- Caffeine increases the activity of

the heart.

- The sinoatrial node (controls the

beating of the heart) has an in-crease in electric activity, which causes the heart to beat at a faster pace.

- There is an increased contraction

and relaxation rate which results in more activity in the ventricles and atria, as well as an increase in the volume in blood pumped dur-ing a specific length of time.

Ethical Issues & Considerations:

Daphnia are very small with a less sophisticated nervous sys-tem and are small meaning their are easy to handle carefully, which means that they are going to be less susceptible to pain, as opposed to mammals or bigger animals. They are easily and quickly accumulated in a classroom environment, meaning they do not need to be removed from their natural habit, such as a river, for the experiment to take place. The heart beat of the Daphnia can be recorded without the use of any invasive technique or equipment, unlike those that would be required for a mammal. Carrying out this process requires you to handle the Daphnia very carefully. Unfortunately, Daphnia are not protected by any law stating…., therefore the vulnerability for the invertebrate is not always consid-ered. However, it is important to be mindful of these animals and respect that they are conscious animals who, undergoing this experiment, would be significantly scared. These small invertebrates are being taken from their pond water environ-ment and transferred in a narrow pipette, which would be frightening, and so the transportation of the Daphnia should be quick but careful.

The lamp from the microscope produces heat, which can warm up the water that the Daphnia are surrounded by on the slide which, as well as increasing their heart rate, could harm the crustaceans. Therefore, the time that they are left under the microscope must be monitored and kept short. Daphnia’s natural environment is that of pond or river water as it is of the correct pH and minerals. Tap water and the caf-feine in the solutions are an unnatural environment for these invertebrates and could potentially harm them. The time they spend in these solutions must also be kept brief to ensure minimal harm comes to the Daphnia.

Carrying out the experiment

The equipment needed for this experiment includes:

Glass slides; Microscope; Caffeinated energy drink; Daphnia in pond water; cotton wool; pipettes; timer; beakers;

Gather a sample of Daphnia in a beaker with enough of their pond water to stay in. Take 2 beakers, in the first, place a quantity of purely caffeinated energy drink, the next with a 1:1 ratio of energy drink and tap water. On a glass slide, create a barrier with a small amount of cotton wool, so that the invertebrates stay still. Using the pipettes, pick up one of the largest Daph-nias from the beaker of pond water and place in onto the slide within the cotton wool barrier. Position the slide on the microscope and locate the heart, so that you are able to clearly see the heart beats. With a pen and paper, dot the paper each time the heart beats for a duration of 30 sec-onds. Immediately remove the Daphnia from the slide and place back into the pond water. Count up the dots and times the number by 2 in order to get the bpm. Take the pipette and carefully remove a different larger Daphnia. Place it into the 50% caffeine solution, and time for 30 seconds. Once the time is up, remove the Daphnia and place onto a glass slide and then repeat the method for recording the heart rates. Repeat this method with the 100% caffeine solution.

Independent variable: Concentration of caffeine

Dependent variable: Heart rate of the Daphnia

Control variables: Time spent counting the heart rate; form of caffeine used; time Daphnia spend in caffeine solution; age of daphnia; size of Daphnia; pre-treatment of Daphnia; temperature of surroundings; oxygen concentration in water; (every aspect besides independent variable should be controlled)