Daphnia Heart Rate Experiment

The purpose of the experiment is to examine the impact of the drug Caffeine on the heartbeat of a Daphnia. This investigation can offer valuable information about its effects on human heart rates. The use of Daphnia guarantees an impartial and secure experiment. These organisms, also known as water fleas, are crustaceans that belong to the arthropod group in the Kingdom Animalia.

They possess an open circulatory system whereby fluid (there is no differentiation between blood and nutritional fluid) is transported in the hemocoel to deliver oxygen and nutrients directly to the organs/cells, resulting in caffeine entering their system at a much faster rate compared to humans. This kind of circulatory system depends on diffusion and its swiftness, which explains why most organisms with open circulatory systems are small in size. Additionally, their transparent bodies make them perfect candidates for this experiment as it allows for easy observation of the heart under a microscope.

The living organisms’ ability to thrive greatly depends on the habitat they reside in. Factors like salinity, dissolved substances, oxygen levels, pH balance, ammonia concentration, and temperature all play a crucial role in this process. [pic] Caffeine is a widely used stimulant drug with psychoactive properties that significantly impact various aspects of the body. These effects include mood swings, the cerebral vascular system, stamina, digestion (including colonic activity), and more. It remains uncertain whether caffeine can be classified as an addictive substance since it is often consumed for pleasure or specific purposes. Previous studies have suggested that if the body has not developed tolerance to it yet, caffeine can act as a diuretic. The absorption of caffeine into the bloodstream takes around 45 minutes before reaching the heart where it binds to specific receptors and increases heart rate by affecting heart muscle contractions and relaxations.

Hypothesis and Null Hypothesis:

Hypothesis- I hypothesize that exposing a daphnia to caffeine will cause an increased heartbeat. Furthermore, I hypothesize that different concentrations of caffeine will not affect the daphnia’s heartbeat differently.

Variables of the experiment:

Independent- The independent variable was the concentration (%) of caffeine solution given to the daphnia.

Dependent- The dependent variable was the heart rate (beats per minute) of the daphnia.

Control (independent) variables: • The volume of water given to under the microscope • The size of the • The same species of And there were more that were hard to control e.g the age of the as this was unknown.

Hazards and Ethical Issues:
|Problem it could cause: |How it can be solved:
The glassware could have smashed and now be on the floor.|There could be a cut or injury if it is cleared away by hand.|Use a dustpan or brush to clear it away.
The heat from the microscope evaporates the water around .|The could die without enough water.|Give the enough water to survive and enough to not be evaporated. Also do not keep water under microscope too long.
The could die due to too much exposure to caffeine.|The would die due to a heart attack.|Use a different for each caffeine concentration.
Once finished with the , put it into the separate tank of pond water so it is not reused.By ingesting bacterium or viruses from the pond water.|The person that ingested bacteria could contract an infection.|Wash hands after investigation to remove bacteria from hands that touch mouth regularly.If the daphnia is handled roughly, it could result in injury. This could then affect its heart rate, potentially impacting the experiment’s results. To prevent this, it is important to handle the daphnia carefully by using a pipette instead of fingers that may squash it. Moreover, when conducting the experiment, it is crucial to use an adjusted pipette that does not trap or cause stress to the daphnia as this can influence the outcomes. In order to address ethical concerns and ensure both human safety and the well-being of the daphnia, a pipette with a large hole has been employed to avoid any harm or distress. The necessary equipment for this experiment includes a daphnia tank, microscope, cavity slides, 1ml pipette and syringe, 10ml beaker, stop clock, pond water, and caffeine solution. The method involves extracting a daphnia from the tank using a cut-off end pipette and placing it in a resting beaker. Then collecting all required equipment and adjusting the microscope to its lowest magnification setting. Using a syringe specifically for gathering pond water mixed with 0.25% caffeine solution gradually increases concentration levels until desired effect is achieved.Finally observing one daphnia on a cavity slide under the microscope.

First, allow the daphnia to adjust for a minute or two. Then, using the stop clock and board marker, count the daphnia’s resting heartbeat in 15 seconds by drawing a dot on the table for every beat (repeat this process to obtain an average). To calculate the heartbeat per minute, multiply the beats per 15 seconds by 4. Next, remove the daphnia from under the microscope and add some 0.1% caffeine solution to it. Place the daphnia back under the microscope and allow it to adjust again. Finally, using the stop clock and board marker, count the daphnia’s heartbeat in 15 seconds by drawing a dot on the table for every beat (repeat this process to obtain an average).

Calculate for 1 minute again. After completing the calculation, transfer the daphnia to a tank of fresh pond water to allow it to recover from the caffeine’s effects. Repeat this procedure with various concentrations of caffeine solution and use a different daphnia each time. The results are shown in the table and graph below: [pic] [pic] The discussion reveals that as the concentration of caffeine solution increased, the heart rate of the daphnia also increased. For example, the heart rate was 249 bpm with a 0% caffeine solution and 328 bpm with a 0.5% solution, indicating an increase.

The graph shows a positive relationship between caffeine, the independent variable. Caffeine is a stimulant drug that binds to receptors in heart tissue and increases heart rate. This attachment enhances ATP levels, which control heart contractions and relaxations, resulting in an increase in the number of heartbeats per minute. Similarly, when observing daphnia under the microscope, this study found that caffeine also increased their heart rate. Different concentrations of caffeine resulted in varying degrees of heart rate elevation.

To summarize, the null hypothesis was disproven when comparing the heart rate increase from a lower concentration of caffeine (0.25%) to a higher concentration (0.5%). The heart rate increased by 13 bpm with the 0.25% solution and by 79 bpm with the 0.5% solution. However, inconsistent results from other groups raised concerns about the experiment’s reliability. Notably, one group’s results for the 0.5% concentration (highlighted in bold in the table) displayed significantly lower values (181, 216, 194), which were likely caused by a counting error specific to that group.

Multiple variables can influence the heartbeat of Daphnia, such as stress levels, the speed of the heartbeat counter, age, and gender. Other factors can also affect it. To improve reliability, it is advised to use Daphnia of the same gender in order to eliminate any potential gender-related influences on heart rate.

To enhance reliability, an alternative approach involves utilizing tape to fasten the daphnia beneath the microscope and subsequently projecting their image onto a sizable screen. By adjusting the film’s speed, the individual conducting the count can more conveniently ascertain the beats per minute. Additionally, granting the daphnia additional time to acclimate to their surroundings may aid in reducing stress levels. It is crucial to note that this could potentially impact the experiment’s validity since there might be multiple variables influencing the daphnia. Nevertheless, solely one variable was modified in this specific experiment: caffeine solution concentration.

Even though attempts were made to reduce external influences, the experiment was deemed valid and fair. Nevertheless, its precision was affected as the findings deviated considerably from online sources and literature.

References:
Figure 1- http://www.caudata.org/daphnia
Figure 2- http://www.evolution.unibas.ch/ebert/publications/parasitismdaphnia/img/full/ch2f5.jpg
1&2- http://www.medicinet.com/caffeine/article.htm

Figure 2 provides the following information:
Figure 1- H- Heart B- Brain CE- Compound eye