I will also control the possibility of impurities in the water by using tap water for the duration of the experiment. This will ensure that the water I use will have the same amount of impurities in it, for example there may be fluoride in the tap water, but as long as it is a constant amount each time it should not effect the experiment too much.
The temperature of the water will be varied with the use of ice and water heated by a kettle. I will measure the heart rate over 30 seconds to provide a balance between accuracy and number of results, as I only have a limited amount of time to obtain my results.
Preliminary testing
These are my rough trials; the temperatures are not exact, however they are close enough for a rough trial. From this rough trial I realised that I did not have the stamina to keep counting for 30 seconds so I have decided that I am only going to count for15 seconds. This will help me to count more accurately. I have also found that the Daphnia dies at 40oC, therefore I will only go up to 35oC in the actual experiment.
Improvement of Initial Plan
To improve my original method I have decided that instead of counting the heart rate for 30 seconds I have decided that I will only do it for 15 seconds as I have not got the stamina to keep an accurate tally for 30 seconds since pushing the clicker counter for over 200 times a second makes my hand weak.
I cannot use water colder than 0oC because enzyme activity would cease altogether; I cannot use water hotter than 40oC because the enzymes would be damaged and the Daphnia would die.
Final method
I will use the following equipment:
1 microscope
1 lamp to light the Daphnia
1 fluid slide
1 clicker counter to count the heart beats
1 stop clock
1 pipette
1 thermometer
1 beaker to hold the Daphnia in their new environment
1 kettle
some ice
some water
Prepare a new environment for the Daphnia in a beaker and add a thermometer. Use ice and water heated from a kettle to bring the water up to the desired temperature. Fill the beaker up to 150ml.
Place a few Daphnia into the environment and let them acclimatise for 3 minutes.
Prepare a fluid slide on the microscope and set it to lowest magnification.
Remove a Daphnia from the environment with a pipette and place it on the slide.
Start the timer and use the microscope and clicker counter to measure the heart rate.
Repeat with same Daphnia if possible.
Prediction & Scientific Information
As you can see I think that the heart rate of our specimen will rise as the temperature rises from 0oC, to around 25oC. After this point it will drop until the temperature of the water becomes to great for the Daphnia to remain alive in.
The reason that I think the heart rate will do this is to do with enzymes. Enzymes control the metabolic rate of any living organism, therefore as the temperature rises, so to does the energy of each enzyme and it carries out its job more effectively. When the temperature gets too hot the enzymes’ active site begins to disfigure and the enzyme becomes useless. As a result the organism will slowly die. When the organism becomes too cold the enzymes will cease to function correctly without energy. If I were to sketch a graph of the heart rate I predict it would look like this.
It is easier for something like this to happen to a Daphnia than a human because a Daphnia has no control over its body temperature, therefore it is much more easily affected by the surrounding water than a human would be in air.
When a human is dying, their heart rate slows down, therefore when it is too cold or too hot, the Daphnia begins to die too.
Results and analysis
These are the results that I obtained during my experiment:
Looking at the graph (overleaf); it can be seen that the Daphnia has a slower heart rate at lower temperatures and the graph peaks out at 25oC where it has the highest heart rate. The graph starts to dip slowly after this peak. This looks quite like an enzyme activity graph, where the activity builds up as the temperature builds up, peaks out a certain temperature and then falls rapidly as the enzymes are destroyed. If I were to do more experiments at higher temperatures, the graph would fall very rapidly as enzymes used for key purposes such as digestion are destroyed. The Daphnia would shortly die after this. The graph may not be very accurate, as the results for 5oC are not as low as they should be for an enzyme graph.
However, it would be logical to say that the heart rate is proportional to enzyme activity as the heart rate mimics the temperature enzyme activity as the water temperature changes. The heart rate is relational to metabolic rate, which is controlled by enzymes. If enzyme activity falls, the metabolic rate falls, and less food is being processed. This means that fewer nutrients are needed to be pumped around the body for bodily functions. When enzyme activity rises, the metabolic rate increases because more food is being processed so more nutrients can be distributed around the body; therefore a faster heart rate is needed to pump these nutrient around. This is what my prediction explained earlier, so I was right in saying that enzymes play a great role in the heart rate and that is related to metabolic rate. The results support the prediction.
Analysis of graph
As you can see there is a curve made by the line of best fit, this indicates that my prediction was correct and that after a certain point on the graph (25oC), the line begins to drop.
As you can see I have highlighted one of the points on the grid as being an anomalous result. I think that this result was anomalous because one of the results that made the average for this point was particularly high (35oC, test 3). I think that this was a particularly high result because whilst I was counting the heart rate of the Daphnia, it moved, this caused me to panic and over compensate by counting faster than the Daphnia’s heart was actually beating.
Conclusion
When the temperature of the surrounding water of a Daphnia increases, the enzyme activity increases and metabolic rate increases until the temperature reaches the enzymes maximum thermal threshold. After this, the active site of the enzyme begins to disfigure and the Daphnia dies soon after as digestion stops without enzymes.
I feel that now is an appropriate time to mention the Q-10 law. This law states that for every 10oC increase in temperature, the rate of an enzyme controlled reaction doubles.
There is an equation for this law: Number of beats at T (temperature)+10
Number of beats at T (temperature) =2
This law was developed to test the accuracy of the obtained results. The answer should always be 2. I will now test one of my results to see how accurate I actually was: the temperature I will take the results from will be 5oC:
224+10 = 234 = 1.0(3sf)
224
This proves that my experiment was not nearly accurate enough. This is I think, due to (see Evaluation)
Evaluation
My procedure worked well and allowed us to collect a sufficient amount of data in support of my predictions. The predictions I made were correct. There were, however, a number of limitations of the experiment, which have clearly had an effect on the accuracy of the results obtained. As I was using temperature as my main variable. It was difficult to maintain the correct temperature of the water on the slide. One of the problems was the heat energy that had been transferred from the light to the water on the slide. This would have made the water warmer. Also the amount of water you have on the slide would effect the temperature because, if you have a small volume of water, it will cool down or warm up more quickly than a larger volume. For example if you have a small volume of water at 40oC it will only stay at that temperature for roughly 4-5 seconds, and this is not sufficient time to do 3 experiments that are each 15 seconds long.
The counting is another thing that would not be as accurate as possible because of human error. We could miss-count or (when using a clicker counter) slip. Another thing is the speed at which the Daphnia’s heart beats. The human arm is not adapted to moving as quickly as cardiac muscles; also cardiac muscles do not get tired, as arm muscles do. The Daphnia frequently died and therefore had to be replaced. This meant that the same Daphnia could not be used for a long time, thus meaning that we could not conduct a fair test due to the Daphnia differing Heart rates.
The volume of water we used was not sufficient for the Daphnia to breathe as normally. This in turn could effect the heart rate of the Daphnia, but if we added any more water the Daphnia would have too much room to move, and this would make it nearly impossible to count the heart rate of the Daphnia.
It would have been very useful to repeat the experiment many more times. We could have gone up 1oC every time to give a greater degree of accuracy. We could also have used a narrower temperature range. E.g. 1oC, 2oC, 3oC. I could also have allowed the Daphnia to acclimatise in a thermostatically controlled water bath.
Lastly I could have done the experiment in bright daylight, thus eliminating the need of a lamp. This in turn would eliminate any extra heat coming from there. The fact that I timed my experiment each time for 15 seconds meant that to obtain the results for a full minute I would have to multiply the results by 4. This would compound the accuracy of the results obtained.
Matthew Young 11JSM2 Page of
11B3
