Organisms can also be placed in two groups depending on the way they cope with environmental fluctuations. They will either be a regulator or a conformer. An animal is a regulator if it maintains nearly a constant internal environment over a range of external conditions. This means it uses the mechanism of homeostasis (the steady state physiological condition of the body) to moderate internal change in the face of external fluctuation (1). Endothermic animals, such as mammals, are regulators. They keep their body temperature within narrow limits in spite of external changes in temperature. Conformers allow their internal environment to vary. They allow conditions within their bodies to vary with certain external changes.
Daphnia are ectotherms and conformers. This is because their internal temperature varies according to external temperatures (1). If one looks at a graph that shows the relationship between body temperature and ambient temperature in an ecotherm and endotherm, one will see from that graph that the line which represents an ectotherm rises steadily, while the line representing an endotherm remains on a level plane. Then, when one looks at a graph which shows temperature versus metabolic rate of a Daphnia, one will find that this line also rises, much in the same way as the ecotherm rises on the first graph (1,2). This data proves that Daphnia are ecotherms. As Daphnia’s metabolic rate increases, so does their heart rate in order to supply oxygen to the heart and body. As heart rate increases temperature will also increase because more reactions will take place. DOES THIS MAKE SENSE???
As temperature increase, more ATP is produced for the contraction of the heart muscles. Temperature facilitates enzymatic reactions which cause cell respiration, which produces ATP. ATP is what is used for energy with in the body and what controls heart rate. As body temperature decreases, less ATP is produced through cellular respiration because there are fewer reactions and the reactions that are occurring slow down. This means the heart rate will also be lower, meaning less oxygen to the body. As the temperature increases, so do the enzyme reactions. This means an increased amount of ATP will be used, therefore more oxygen needed which leads to a greater production of carbon dioxide. This acts on the heart rate to increase delivery.
Although this particular experiment is being done on Daphnia, it relates to larger issues in the field of biology. It is easy to test the effect of temperature on heart rate on such a tiny organism such as daphnia, but the results from the experiment can be related to larger creatures. When a human is out in the cold for extended periods of time, one may notice it is more difficult to move their extremities such as fingers or toes. This is because the decrease of temperature causes less ATP to be produced. With less ATP being produced, the body has trouble functioning because there is not enough energy being supplied to the body, which makes body functions difficult. With a temperature decrease, blood is moved away from extremities in order to try and maintain a core body temperature. This may cause skin to become cool and pale. As well, lower temperatures mean that internal reactions slow down. This means there is less demand for oxygen because the metabolism is slowing down as well. There are large animals in the Artic, simply so they do not lose heat. If they loose too much heat, and there body temperature lowers, the reactions inside there body that produce ATP will slow done, thus making their body function slower.
Method:
Collect 9 depression slides. Place three in a beaker of ice at a temperature of 4oC, three in a beaker of 30oC water, and three just sitting at room temperature (about 20oC). Use a thermometer to ensure you have the right temperatures. Let the slides sit at their given temperatures for at least 5 minutes, allowing slides to cool down or warm up.
Now, collect three daphnia by using a plastic pipette. Place these daphnia in a small beaker of water when they are not being tested. Daphnia are very fragile organisms so they must be handled carefully and with respect.
Remove one depression slide from the beaker of ice (make sure the beaker is at the right temperature). Use Vaseline or petroleum jelly to line the edge of the depression found in the centre of the slide. You must be quick when doing this because you do not want the slide to warm up. By using the pipette again, collect one daphnia from the beaker, and place it on the slide, on the depression in the circle made by the jelly. Next, use the microscope to magnify the daphnia. Once the daphnia can be seen clearly through the microscope lens, count the daphnia’s heart beat per minute. The easiest way to do this is by counting the number of beats for ten seconds, and then multiplying that number by sixty to get the heart beats per minute. Record this number in a data table. Repeat this procedure with the two other daphnia. Each temperature will require three trials. Next, take a slide that was sitting at room temperature and repeat same procedure with it as was done with the cold slides. Remember to do three trials at this temperature also and record results in a table. Finally, repeat these steps with the three slides that were placed in warm water. Again, three trials must be done and all results must be recorded in a data table. Once this has been completed, return equipment to proper places and clean up area. Return daphnia to their environment.
Table 1: The Effect of Temperature on the Heart Rate of Daphnia (rough data)
Table 2: The Effect of Temperature on the Heart Rate of Daphnia.
*Note: results in each trial were averaged from class’s data.
Table 3: The Effect of Temperature on the Q10 of Daphnia
Calculations: (Q10 values calculated relative to room temperature.)
Q10 cold = Heart rate at room temperature/Heart rate at cold temperature
= 170.9/152.3
= 1.121
Q10 Warm= Heart rate at room temp/ heart rate at warm
= 170.9/224.0
= 0.7629
Figure 1:
Figure 2:
Results:
As can be seen in Table 1 and 2 and Figure 1, as temperature increased, so did heart rate. When the temperature was 4oC, the average heart rate of the Daphnia was 152.4 beats per minute. When the temperature was 30oC, the heart beat of the Daphnia was 224.0 beats per minute. As can be seen in table 3 and figure 2, the Q10 of the Daphnia decreased as temperature increased. The Q10 at 30oC was 0.763, and the Q10 at 4oC was 1.121. The overall trend on data is easily seen in Figure 1 or Figure 2.
Discussion:
As can be seen from the results section above, as temperature increased heart rate also increased, but the Q10 decreased. These results are not surprising to me, and I hypothesized that these results would be found. Daphnia are categorized as ectotherms, which means that their internal temperature is influenced by their external environment and they do not thermoregulate (like mammals) (3). They are, however, thermoconformers, with little control over their body temperature (1). Therefore, when the environmental temperature increases, so will the internal temperature of the Daphnia. The chemical reactions that occur in the cells of Daphnia are dependent on certain enzymes, or proteins, to help the reactions proceed. As the temperature of the environment increases, the metabolism of the Daphnia increase as well, because chemical reactions occur faster at higher temperatures (1). This means that the heart rate will speed up in order to provide oxygen to the cells as the metabolism increases. However when the external envronment reaches a certain temperature (around 40oC), the enzymes break down, and the chemical reactions can no longer occur, so metabolism stops and the Daphnia dies (3). This was not experianced in this particular lab because temperature never exceeded 30oC.
Daphnia, and other ectotherms can acclimatize to their environment by adjustments at their cellular level. Cells can increase the production of certain enzymes which helps to compensate for the lowered activity of the enzymes which occurs at lower temperatures (1). Also, cells can produce heat-shock proteins which help to maintain the integrity of other proteins that would be killed by such extreme temperatures (1). These proteins help prevent cell death when an organism is challenged by severe changes in cellular environments.
Next time when this experiment is done, I will make sure that when I take a slide out of either the hot or cold water that I move quickly so the slide does not change temperature. This will ensure more accurate results, as the whole point of the experiment is to test the effect of temperature on the heart rate of Daphnia. Also, I would be extra careful to make sure that the Daphnia are not exposed to air. This will eventually kill these organisms if air is allowed under their shell. I do not want to harm these creatures, and want to be able to release them back into their environment when I am finished with them! As well, in order to have the fairest of results, I would be sure not to remove the Daphnia out of their natural environment prior to observing them. I would just take them one at a time as I needed them from the large jar they are collected in. Finally, I would want to collect all data myself instead of sharing data with classmates. This way I would be able to make sure that all variables are controlled, and I will feel more confident in my end results.
This was a test of a fair test because the average variation was less than 10% of the trial average. As well, all variables that were possible to control, were controlled. There will always be some variation in experiments, but in this particular one it was impossible to control all variables and it is impossible to control all natural biological variation (such as age, disease). All variables that I did have control over, were controlled such as temperature and surroundings.
References:
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Campbell, Neil A. and Jane B. Reece, 2002. Biology-6th edition: San Francisco: Benjamin Cummings. Pp
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SBI4U Lab Manual 2004-2005. Evolution and the Nature of Science- Part 1. Author. Ms. Davis
- Environmental Inquiry [Online] Available http://ei.cornell.edu/toxicology/bioassays/daphnia/, October 9, 2004
