I also think this because in humans during exercise, the body temperature rises; therefore the heart rate increases because more oxygen is needed. So I also thought this could be true of Daphnia, even though human temperature is controlled through homeostasis. I also believe it will be harmful for the Daphnia to be exposed to 40 degrees C or more, and that they could possibly die. The reason for this will be because as an ectothermic organism, its body temperature will also be rising with no ability to control it. Another reason for increased heart rate is enzyme activity. The chemical reactions in the body will happen faster due to the increased temperature, consequently the heart rate will speed up to supply more oxygen to the respiring cells. When there is a decrease in temperature the heart rate will decrease also, as cell respiration is happening less.
Equipment
The equipment I intend to use is as follows:
- A culture of Daphnia
- A microscope
- An animal cell and a spare cover slip
- A Petri dish base
- A pipette
- A paintbrush
- A small beaker for collecting water
- A thermometer
- A basic electronic calculator
Planned method
I have decided to measure the heart rate of the Daphnia at the temperatures: 150C, 200C, 250C, 300C, and 350C. This is so I can get a good representative sample of the change in heart rate. I will control the temperature by changing the water temperature in the Petri dish, by way of adding hot water to the dish with a pipette. I have chosen to stop my investigation at 350C as any higher than this could cause the Daphnia to die*. I will leave the Daphnia’s immersed in the water of each new temperature; for at least 2 minutes, so they can acclimatize themselves to the new temperature, leading to a more accurate result. Daphnia’s are excellent organisms, in which to carry out this experiment, due to their clear exoskeleton, which allows excellent visibility of the heart. Once the Daphnia’s have acclimatized to their new temperature, I will place them under the microscope (I would have previously practiced counting Daphnia’s heart beats under the microscope) and count their heartbeats. The way in which I will do this will be by using an electronic calculator. I will key in 1++ and then press = every time the heart beats, after 20 seconds I will stop counting and multiply my total by three, thus obtaining how many times the heart would beat in a minute. I will then record my results on a table, for ease of manipulation and then set about drawing up some graphs. The graphs will give a visualization of my results and show standard deviation and mean. Finally I will evaluate my investigation, talking about my findings and discussing how well my hypothesis was on target. I will also discuss how well I felt my investigation went and what I could have done to improve it.
*I realise that Daphnia are living organisms and must be handled with care. I will take extra care when transferring the Daphnia from the cover slip, to make sure they do not get crushed in the cover slip. Once a Daphnia has been studied, it will not be placed back in with the culture as it has been in contact with tap water and may affect the other Daphnia.
Steps I intend to follow
To prepare the small ‘cells’ for trapping Daphnia, take a piece of plastic tubing and slice off a length of 1mm. Place a small amount of ‘super glue’ on the ring and then press it firmly to a glass cover slip.
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Cool water from the tap to 150C by using some ice. Half fill a Petri dish with the cooled water.
- Transfer a Daphnia from the culture to the cover slip, using a paintbrush. Place the Daphnia inside the tiny ring attached to the cover slip. Place another cover slip over the top making sure the Daphnia are unharmed.
- Place the cover slips under the water in the Petri dish.
- Place the Petri dish on the stage of the microscope and look at the Daphnia.
- Find the heart of the Daphnia and practice counting heartbeats.
- Measure the temperature of the water accurately and count the heart rate for one minute using the calculator in the aforementioned manor.
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Draw off some of the water and add water of temperature 200C.
- Once the water has been mixed, measure the temperature again to make sure it’s correct. Count the heart rate again.
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Repeat the above steps again incrementing the temperature by 50C until it reaches 350C.
Risks
There are several factors that can alter the health of Daphnia and may even cause them to die. These include:
- Oxygen. Daphnia can survive in poor water conditions. They have the ability to make haemoglobin, which enables them to survive in an oxygen poor environment.
- pH &Ammonia. Daphnia need the pH of the water to be between 6.5 and 9.5. High Ammonia and pH will reduce the levels of reproduction, but will not actually cause any harm to the Daphnia.
- Minerals. Daphnia are very sensitive to the composition of their environment. Salts such as sodium, potassium, magnesium and calcium can cause the Daphnia to become immobile and they will eventually die.
Variables
There are several factors, which need to be taken into account whilst studying the Daphnia:
- Firstly the oxygen levels must be kept constant, to prevent the Daphnia from suffocating.
- There must not be a high concentration of dissolved minerals such as sodium, potassium, magnesium and calcium to prevent harm or even death to the Daphnia.
- Daphnia are sensitive to pesticides and nitrates, so must not be subjected to these during the experiment.
- The Daphnia must have food to survive, which includes bacteria and micro algae. The food will be present in the tank hosting the culture.
Carrying out a controlled experiment will carefully monitor all of these factors.
Results Table
*The average heart rate will be used to plot the graph.
Finding standard deviation and mean
I am going to find the mean number of heartbeats of the Daphnia throughout the whole experiment.
The standard deviation will be used to see how widely dispersed the results are. The smaller the standard deviation, the less dispersed data is around the mean.
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Therefore, 4.58 is the mean number of heartbeats for Daphnia 1 at 15 degrees Celsius.
This same procedure will be taken out for each Daphnia at varying temperatures.
Analysis
The experiment that we conducted was to see how the temperature of the water affected the heart rate of the Daphnia. My hypothesis predicted that the higher the temperature, the faster the Daphnia’s heart would beat. Additionally I stated one of the reasons I believed this would be true was the Q10 coefficient. Although I did point out it was only a guideline, and while my results did not double or even treble with every ten-degree increment, they did steadily rise. My graphs clearly illustrate this steady rise. As I increased the temperature of the water, the metabolism of the Daphnia increased as well. This is because chemical reactions occur faster at higher temperatures. This means that the heart rate will speed up in order to provide oxygen to the cell as the metabolism increases. This increase of metabolism and subsequent heart rates can be seen in the table of results. However at 400C the enzymes breakdown and the chemical reactions can no longer occur, so metabolism stops and the Daphnia die. In their natural environment, Daphnia would be unlikely ever to experience temperatures of 400C, so this is improbable to occur. However they do experience changes in the temperature in their natural environment, and their metabolism will increase and decrease as the temperature changes. By using different temperatures I have been able to link increased temperature with increased heart rate. The results also show that with the decrease in temperature less cell respiration is occurring and so the heart beats at a slower pace.
This table show the results obtained by another group.
These results obtained by another group are fairly similar to the results that we obtained, although the heart rate was considerably higher at 150C, than the heart rate that was counted by my group. This group had a clear optimum temperature, which was 150C. Our results show a steady decrease from 25-350C, whereas these results show a steep decrease, I think this is because the temperature was taken at 100C increments, so the temperatures in between have not been accounted for.
Evaluation
I believe that I followed my method plan well, which in turn led me to produce a set of clear and concise results. These results were shown in tabular form, and also in graphical form (Line graphs). My results were as predicted, the heart rate did increase as the water temperature increased, and as previously mentioned this does coincide with the Q10 theory; not as a rule of thumb, but only as a guideline. If I were to conduct the experiment again I would change the factors that I believe didn’t make the experiment completely reliable, which could result in the graphs not having anomalies which are present on my graphs.
Problems and things I could have changed
There were several factors, which affected the reliability of my experiment:
- Firstly difficulty in controlling temperature. The heat from the light of the microscope heated the water temperature whilst the Daphnia were under observation. This altered the temperature and had a direct affect on the results. Naturally the room temperature also affected the water temperature, at a higher water temperature, the temperature would soon drop, again affecting the validity of the results.
- Cover slip problems. The Daphnia could jump out of the cover slip, which in turn wasted time, then trying to catch it and place it again. I have since learnt from the Internet**, there is a way to counteract this. Apparently using Vaseline on the cover slip, will keep the Daphnia trapped, without causing them harm or hindering the experiment.
- Microscopes. The microscopes were also not beneficial to the experiment. They were very low powered and took a considerable amount of time trying to focus them. Once the Daphnia were in the cover slip, it was sometimes difficult to count the heartbeats, as the cover slip would float around in and out of view.
I think the factors mentioned had a direct impact on my findings in this experiment. The impact of these factor, cause me to doubt the validity of my results. I would like to repeat this experiment several times taking into account these additional points:
- The use of microscopes which did not omit heat
- Use a higher powered microscope
- Use Vaseline to keep the daphnia still
With these points taken into consideration and the opportunity to repeat the experiment several times, would I be totally confident in my results and findings. Only with the repetition, can an experiment be truly validated.
The Daphnia as an ectothermic organism which uses its surroundings to regulate body temperature, would in its natural habitat, be able to cool down by travelling to the bottom of its body of water. Thus in turn, keeping its body at its optimum temperature. In this experiment the Daphnia could not escape the heat as it was confined to the Petri dish, and had to use different ways to cool down. This led to the increase in heart rate as the Daphnia produced a lot of energy as it fought to bring its body temperature under control.
Overall I think the experiment was successful, given its limitations. Which I would change given the opportunity to reattempt the experiment.
**www.can.uni.edu
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If standard deviation is small it shows a small spread of data therefore the data is quite accurate. If standard deviation is large it shows a large spread of data therefore the data is inaccurate. Looking at the error bars on the graph shows this.
