Daphnia, often known as the water flea, is a crustacean. Similar to other arthropods, daphnia contains an open circulatory system. Haemolymph, a blood-like fluid, is passed through the body cavity. Although an open circulatory system may not be as efficient as a closed one, it is perfectly suitable in many organisms similar to Daphnia. You can easily view blood cells through the body as they quickly flow through the body cavity.(Circulation and gas exchange (2018).
Alcohol has different levels of severity for each level of intoxication.
Alcohol enhances into an anaesthetic which acts as a depressant on the central nervous system during intake of higher alcohol levels. It causes the heart rate and blood pressure to decrease dramatically and respiration rates drop to a critical level. One of the early side effects is tiredness and eventually, if a considerable amount of alcohol is taken in, the body will fall asleep. (Study on the Effect of Alcoholic Beverages on the Heart Rate of Daphnia (2018)
Haemoglobin is present in the respiratory system to help oxygen transport.
To increase uptake of oxygen from the water, more Haemoglobin are developed. Daphnia contain a large antenna which is used to direct themselves in the water. Daphnia are found mostly in aqueous environments in large lakes and ponds etc.
They are the food source of Planktivorous fish. The larger the Daphnia, the less likely they are to survive under intense predation. To avoid predators, Daphnia have a well-developed migration technique in which they swim at the top of the water body during the nighttime and swim in the deeper areas during the daytime.
This is done to avoid fish and hide in darker depths. In the daytime, there are plenty of Planktonic Algae which are a great food source for the Daphnia. The optimum pH of Daphnia is between 7.2 and 8.5. (Ebert D 2005).
I expect to find that as the concentration of ethanol increases, the heart rate of the Daphnia decreases as Alcohol is a depressant and slows down the bodily functions.
5 50cm^3 beakers
Heart Rate (beats per minute)
Ethanol concentration (%)
Spearman’s rank correlation coefficient
Mean heart rate (bpm)
The value -1 shows that there is a strong negative correlation in the experiment.The test value (1) is greater than the critical value (0.811) therefore the null hypothesis is rejected. There is enough evidence to show that the concentration of ethanol has a significant impact on the heart rate of the Daphnia.
The results show clearly that as concentration of ethanol increases, the heart rate of the Daphnia decreases. The results of mine are similar those who did the same investigation. There was a few limitations of our method. The fact that we only used 1 Daphnia at a time meant the investigation took longer.
If I was to repeat the investigation, I would do 2 or 3 at a time so there would be more time left over to do the investigation a few more times to strengthen our results.To improve accuracy, we could have started the stopwatch at the same time as when the Daphnia was placed in the beaker instead of a couple seconds after. The investigation was repeated 3 times and the results were similar so the experiment was reliable. Similar results were gained with different methods making the experiment reproducible.
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