Daphnia Heart Rate Experiment

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Experiment Report for: ‘the affect of Caffeine on Daphnia’s heartbeat’


Aim: The aim of this experiment is to understand the affect of the drug Caffeine on the rate of a Daphnia’s heartbeat. This is to understand the affect of caffeine on a human’s heart rate and the use of daphnia keeps the experiment fair and safe.

Background Research:

Daphnia –

Daphnia (water fleas) are grouped as crustaceans under the arthropod group of Kingdom Anamalia. They have an open circulatory system where fluid (there is no distinction between blood and nutritional fluid) in the hemocoel delivers oxygen and nutrients to the organs/ cells directly meaning caffeine enters their system much faster than it would in humans. This type of circulatory system relies on diffusion and it being fast which is why the majority of organisms with open circulatory systems are small. They have transparent bodies which make them ideal for this experiment so the heart can be observed easily under the microscope. They are very particular about the habitat they live in and whether they flourish in an area can be brought down to levels of: salinity, dissolved substances, oxygen, pH and ammonia and temperature.


Caffeine –

Caffeine is known as a psychoactive stimulant drug and it is the most widely used stimulant. On average 90% of adults consume it on a daily basis. The drug has an effect on mood swings, the cerebal vascular system, also can have a profound effect on the body’s stamina and processes through digestion including colonic activity. It seems that people are not sure it caffeine is an addictive substance as it can be consumed for what people call purpose or pleasure. Some past research has shown that it is has a diuretic effect on the body especially if it hasn’t built a resistance to the drug. Caffeine takes about 45 minutes to be absorbed into the bloodstream. Once the caffeine has reached the heart it attaches itself to specific receptors causing the heart rate to increase. It increases due to increased levels of ATP which affect contractions and relaxations of the heart. These increased levels cause the heart to beat faster.

Hypothesis and Null Hypothesis:


I hypothesize that if I put a daphnia into a caffeine solution then the caffeine will cause an increase in the daphnia’s heartbeat.

I hypothesize that different concentrations of caffeine shouldn’t have a different effect on the daphnia’s heartbeat.

Variables of the experiment:

Independent- The independant variable of the investigation was the the concentration of caffeine solution given to the Daphnia (%)

Dependant- The dependant variable is the heartrate of the daphnia (beats per minutes)

Control (independant) variables:

• The volume of water given to daphnia under the microscope

• The size of the daphnia

• The same species of daphnia

And there were more that were hard to control e.g the age of the daphnia as this was unknown.

Hazards and Ethical Issues:

|Hazard/Ethical Issue: |Problem it could cause: |How it can be solved: | |The glassware could have smashed and now be |There could be a cut or injury if it is |Use a dustpan or brush to clear it away. | |on the floor. |cleared away by hand. | | |The heat from the microscope evaporates the |The daphnia could die without enough water. |Give the daphnia enough water to survive and| |water around daphnia. | |enough to n ot be evaporated. Also do not | | | |keep wter under microscope too long. | |The daphnia could die due to too much |The daphnia would die due to a heart attack. |Use a different...
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