How caffeine affects daphnia heartrate

Aim:

How caffeine affects the heart rate of Daphnia (water fleas)

During this experiment we were examining the effects of different concentrations of caffeine on a type of water fleas called daphnia; the heart-rate is the dependant variable and the concentration of the caffeine is the independent variable.

We tried to keep all of the other variables constant by controlling them. Such as the room temperature; the volume of caffeine; the type of water fleas ect.

Our hypothesis is that as the caffeine increases so will the heat rate of the daphnia. This is because caffeine is a stimulant that increases the amount of neurotransmitters being released and therefore the production of the heart.

Equipment:

A culture of Daphnia in a beaker of water
A microscope- with two cavity slides
Two dropping pipettes- one with a large mouth and one with a small opening
Cooled Distilled water
Cotton wool
Paper towels
A stop clock

Method:

We picked out a couple of daphnia from the culture in the beaker with the pipette that has a big mouth.
Then, we got rid of the excess water, by squeezing the pipette to get rid of the extra water onto a paper towel.
Then, one of the daphnia was placed onto the small bit of wool which was on the cavity slide.
After that, we placed a small amount of cooled distilled water onto the second cavity slide before putting that underneath the first cavity slide directly under the daphnia.
Then we put both cavity slides under the microscope.
Afterwards, we counted the amount of heart beats for the daphnia for 5 minutes.
We repeated this three times.
Next, we measured out our volume of 0.25M of caffeine and gave that to the daphnia and counted its heart beats for 5 minutes. Then we did it again 2 consecutive times before stopping.
Then we repeated this procedure with another water flea but this time instead of adding the 0.25M of caffeine we added the same volume of distilled water. We repeated this once.

Our results table for caffeine:

Our results table for distilled water:

Graph of results:

186-167

In conclusion:

From my results we can tell that the relationship between the caffeine and the heart rate is that as the caffeine increases so does the heart rate. This means, caffeine ∝heart-rate.

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Our results table for caffeine:

Our results table for distilled water:

Graph of results:

186-167

In conclusion:

From my results we can tell that the relationship between the caffeine and the heart rate is that as the caffeine increases so does the heart rate. This means, caffeine ∝heart-rate.

This is as I predicted that this would happen because caffeine is a stimulant drug. This is true as on average the caffeine had 19 more beats per minute than no caffeine. As I mentioned before, this is because the caffeine increase the production of neurotransmitters. Neurotransmitters are the chemicals which allow the transmission of signals from one neuron to another across synapses. They are also found at the endings of motor neurons, where they stimulate the muscle fibres. This means that if the caffeine increases the amount of neurotransmitters that will then consequently increase the stimulation of the muscle fibres and that increases the activity of the heart; causing the heart to beat faster than normal. The results table also shows that the higher the concentration the higher the amount of heart beats.

Evaluation:

All in All, in my opinion the experiment was good as it showed good results that supported my hypothesis and was scientifically sound.

However, although I did try to make it as reliable as possible we still need to take into consideration human error which is present here. For example it was very hard to keep in time with the daphnia’s heartbeat as it was going very fast and was hard to count. So, at time we may have been counting too slow or too fast. This means that is the data we did have some anomalies that I did not count when making the final averages.

To make our results more reliable we also repeated them as many times as we could. We repeated three times for the caffeine which made the results for the caffeine more accurate and dependable. But, we ran out of time for the distilled water (which was our control to compare with the caffeine) and therefore its average is not as reliable as we would have liked.

To make sure our results we valid we tried to control all the other variables other than the concentration of the caffeine (all which I stated in the introduction). This includes the temperature of the daphnia. It must be understood that the daphnia are living organisms and need to be treated right in the experiment. So, to look after and keep them cool we put the cool water underneath the slide they were on. Another thing we done was when we were not using them we took them out from under the hot light of the microscope so that they would not burn.

If I were to do this experiment again I would make sure that I had enough time to repeat both experiments more times to make it more reliable. Also, I would use some kind of data logger to measure the heartbeat of the daphnia; this would eliminate the chance of human error. To make it even more valid I would try to use the same daphnia each time and use a thermometer to see the temperature so it would be easier for be to regulate it.

Teacher Reviews

Here's what a teacher thought of this essay

Luke Smithen

23rd of Jul 2013

This is a well written report. 1. The start of the report is quite brief and is missing several sections, such as a safety section. 2. The tables of data are well presented. 3. The conclusion should use data from the tables to back up the patterns and should also refer to the graph. 4. The evaluation should suggest further research opportunities. ***

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