Locate the hear and count the heart beat for 15 seconds. Multiply by 4 to give the rate per minute. Repeat several times. Return the daphnia to the container and repeat using at least two other similar sized animals. Collect the class results. Record your results as a table.
All counts should be made as quickly as possible as the daphnia may not be able to survive in the new environment. Temperature will also varies, which would affect the daphnia's heart beat as they are sensitive to the fluctuation of the temperature.
Results
Table shows the average heartbeat per minute of each daphnia that were counted in the class
Tally chart showing the frequency of each group with a range of heartbeats per minutes (min-1) internals of 5.
Table showing the calculation of plotting a histogram
Mean : Σ ( all the frequency)/50 = 192 heartbeat per minute
Median : (50+1)/2 = 25.5th term which lies in the group of 196-200 heartbeats per minute
Mode: 212 heartbeats per minute
Analysis
The hypothesis is proved that on an average daphnias have heartbeats of between 190 to 200 per minute. This is shown by the histogram which I have plotted with the results collected above. The histogram shows that there is a wide range of heartbeats per minute. However there is one anomaly which the daphnia that was observed who has only an average of 81 bpm, this might be at an old age or ill which lead to a rather small heartbeat per minute compare to others. There were most daphnias with their heart beat between 195-200 bpm, and from the histogram, it also suggested a range of heart beat per minute for all the daphnias that were observed, the range is 135-253 bpm.
The results were also used to calculate the mean, mode and median. It shows that the average heart beat per minute of all the daphnias studied are 192 bpm. The median of the frequency lies in the group of 196-200 bpm, which fits well with the average as well as the histogram. As the group has the highest bar of the histogram. The mode ( the most common number) of the frequency is 212 bpm.
Evaluation
There were one or two anomalous results from this experiment, this could be due to many number of faults these include, ill daphnia, sufficient water in the cavity for the daphnia, daphnia was not adapted to the new environment yet and so on.
The heart beat of daphnia may become irregular due to the fact the daphnia's small mass and surface area would struggle severely to cope with the change in the environment and this irregularity could perhaps result in death.
An attempt was made to use the same daphnia and repeat the experiment 5 times before replacing it into the container as daphnia's vary in size and metabolic rates. Also the age of the daphnia can have some effect, although some only live a matter of minutes, like any other animals, their metabolic rates vary depending on age, size an characteristics.
With the equipment in use, it was impossible to know whether the daphnia is ill or in a poor state, so in unlucky an ill daphnia could alter the entire experiment. Further equipment such as extremely accurate thermal probes, or other physical assessment tools would be necessary if conducting an extremely accurate investigation.
Although the female daphnia population is in excess of the male, if a male daphnia was taken for the experiment it would make results differ due to the fact that it is difficult to distinguish male an female daphnia. They are identical except that males are generally smaller in size, have larger antennules, and the first legs have a stout hook use in clasping the female during mating. Rather than trying to identify males to detect stressful environments, it would be much simpler to inspect the brood chambers of females, i.e. if a male daphnia was use, the results would differ greatly.
Daphnia stress levels can also alter results, in as much as if the daphnia has a high blood pressure (hyper tension), it would be most likely that they will have higher heart beat than average.
On one or two occasions it was impossible with the equipment provided to count the daphnia's heart beat. Neurotic sensors would be ideal for counting the BMP's of the daphnia's heart.
Also factors such as the heat from the lamp of the microscope, raising the temperature must be considered, as it is known that daphnias do not thermo regulate.
If a pipette was contaminated with another substance such as distilled water, this could cause interruption the daphnia's original environment, and some would struggle and could causes death.
