To investigate the effects of a depressant on the heart rate of a daphnia.

Sonny Kumar Science Coursework

Biology

To investigate the effects of a depressant on the heart rate of a daphnia.

Background information

Daphnia-What are they and Why use them for Science?

Daphnia are also called water fleas. The most common type is called Daphnia pulex. They are are part of the Crustacean group and can be found in lakes, ponds and small streams. The water that they live is full of nutrients, which is called eutrophic.

Daphnia are used quite a lot in scientific research and are interesting animals for study under the microscope. They are covered in a transparent shell and all internal organs can be seen which makes it good animal to experiment with. You can also see the beating of its heart. This is very helpful in our experiment, as we need to record the heart rate.

Most daphnia are herbivores. Most daphnia feed on bacteria and very small algae. However not all daphnia are herbivores there are some predators such as Polyphemus pediculs.

Daphnia reproduce in summer mostly parthenogenetic meaning eggs develop without fertilization. At the end of the summer some of the eggs develop into smaller males capable of fertilizing the eggs in females, which develop into so called “winter eggs” mostly, one or two present in females. These eggs can be also be found in a population under stress such as the drying up of a pond.

Ethanol-What is it and why use it for this experiment?

Ethanol acts as a drug, effecting the central nervous system. Its behavioural effects stem from its effects on the brain, rather than the muscles or senses. In high doses, the effects of ethanol on human’s produces symptoms such as slurred speech, unsteady walk and inability to walk. This is commonly called being in a state of drunkenness or being drunk.

Ethanol is also called Ethyl Alcohol is the second member of the alphiatic alcohol series. It is a clear colourless liquid with a pleasant smell.

It ...

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Ethanol-What is it and why use it for this experiment?

Ethanol is also called Ethyl Alcohol is the second member of the alphiatic alcohol series. It is a clear colourless liquid with a pleasant smell.

It is difficult to measure alcohol levels in the brain so blood alcohol levels are used to measure the levels of intoxication. Most people begin to show signs of mental impairment at 0.05% blood alcohol. Things become steadily worse until unconsciousness at 0.4% blood alcohol.

Plan

We will examine how daphnia respond top a depressant (ethanol). We will record its response by measuring its pulse rate. To do this, I will use a microscope as in the following plan.

Equipment

For our experiment, I will need to use the following equipment-

Microscope- To examine the daphnia and count the heart rate
Cavity slide- To view daphnia while looking through microscope (in the cavity)
Slide cover- To cover the daphnia in the cavity and prevent escape during examination
Pipette- To insert the ethanol on the slide
Syringe- To collect the daphnia and to insert them onto the slide
Beaker- To keep the daphnia in prior to examination
Timer- To count time

Step-by-step plan

Collect and set up equipment.
Select daphnia and extract to slide using syringe.
Soak up excess water using a paper towel to prevent ethanol being diluted.
Add 5 drops of ethanol to the daphnia on the slide.
Place cover on slide.
Add the slice to the microscope and begin counting for 30 seconds
To measure the number of beats I will bang my fist on the table for every heartbeat and my partner will record the amount of bangs that he hears.
Repeat this experiment for the different denominations of ethanol. They are- 0.0%, 0.2%, 0.4%, 0.6%, 0.8%, 1%.
Record the results in a suitable table.

Table of results

Conclusion

Our resulted showed us many things.

Firstly, the general trend was true to our prediction: as we increased the amount of ethanol, the heart rate of the daphnia decreases. However, in several instances, it did increase. We did some research and discovered that in low doses, alcohol can act as a stimulant. This could account for the anomalies we encountered.

Also, our prediction about doubling the Ethanol will halve the heart rate has been proved drastically wrong.

For example: -

0.2% 254

0.4% 233

As can be seen by the above figures, our prediction about that was proved definitely wrong.

One of the main reasons for error is probably the condition of the daphnia. As we are using different daphnia for each test, so we will have different characteristics of each of the daphnia.

For example: -

A larger, healthier daphnia would have a better resistance to the effects of the ethanol than a younger, small, weak daphnia.

Evaluation

I tested the effects of ethanol on the pulse rate of a daphnia.

Our prediction was true in a sense. Although it was proved wrong, as explained in the conclusion, I will now explain why it was incorrect. The influx in he heart rate could be for a number of reasons. One reason could be unnecessary stress to the daphnia, and different states of health. Another reason could be miscounting the hearts beats on my part.

If I was to do this experiment again, I would try to use a more accurate method of measuring the heart rate. Another improvement could be a more accurate way of delivering the ethanol to the daphnia and the daphnia to the slide.

Again as I mentioned in the conclusion, it is important that we obtain the same kind of daphnia. It is unfair to use larger, older daphnia than smaller, younger ones. This would obtain different results. A method of vetting the daphnia beforehand would have to be introduced where only daphnia of the same size are used.

By doing this, then a more accurate set of results would be obtained.