Investigation Into How Alcohol Affects the Heart Rate in Daphnia

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.

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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.

Equipment list:

15 Daphnia

Cotton wool

Light microscope

Cavity slide

10cm^3 pipette

5 50cm^3 beakers

Stopwatch

Ethanol (2%-10%)

Method:

1. Place 5 drops of 2% ethanol into a beaker and use a cut-end pipette to place 1 Daphnia into the beaker.
2. Leave it for 1 minute.
3. Using a pipette, take the Daphnia out of the beaker and place it onto a cavity slide.
4. Use strands of cotton wool to keep the Daphnia in place.
5. Place the cavity slide under a microscope and count the number of heartbeats in 20 seconds and times by 3..
6. Wash the microscope cavity slide and repeat steps 1-6 using 4%, 6%, 8% and 10% concentrations of ethanol.
7. Work out the change in heart rate after adding the ethanol.
8. Repeat steps 1-8 two more times.
9. Present the results onto a table.

Independent variable:

• Concentration of ethanol.

Dependant variable:

• Heart rate in Daphnia.

Controlled variables:

• Volume of ethanol
• Temperature of ethanol
•  Time taken for Daphnia to rest
• Size and weight of Daphnia

Risk assessment:

• Handle glassware with care, if it is dropped wait for the teacher and don't move.
• Carefully move the Ethanol-containing beakers, if any is spilled clean it up straight away with paper towels.
• Do not consume food or drink when handling the Daphnia.

Heart Rate (beats per minute)

Ethanol concentration (%)

1st attempt

2nd attempt

3rd attempt

Mean
2
117
105
120
114
4
102
117
88
106
6
84
81
83
83
8
75
78
69
74
10
72
73
65
70

Spearman’s rank correlation coefficient

Ethanol concentration

Rank

Mean heart rate (bpm)

Rank
D
D^2
2
1
114
5
-4
16
4
2
106
4
-2
4
6
3
83
3
0
0
8
4
74
2
2
4
10
5
70
1
4
16
= 1-2

= -1

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.

Reference list

• (Circulation and gas exchange (2018) [online] Available from:
  https://public.wsu.edu/~rlee/biol103/circulation.pdf accessed 11th June 2018)
• (Introduction to Daphnia Biology Ebert D 2005). https://www.ncbi.nlm.nih.gov/books/NBK2042/)
• (Study on the Effect of Alcoholic Beverages on the Heart Rate of Daphnia (2018) [online] Available from: http://www.ss-pub.org/wp-content/uploads/2016/08/BCR2015063001.pdf accessed 11th June 2018)