An Investigation to Show the Effect of Temperature on Daphnia

An Investigation to Show the Effect of Temperature on Daphnia
An Investigation to Show the Effect of Temperature on Daphnia Plan: I will submerge some daphnia contained in a test tube in water of differing temperatures and measure their subsequent heart rates. Hypothesis I think that the heart rate of the daphnia will increase up until around 40ËšC at which point most of the daphnia?s enzymes will have denatured and rate of metabolism will have stopped or decreased sufficiently to have stopped the daphnia?s heart rate. Apparatus list Test tube Beaker Different temperatures of water Daphnia Pipette Stop clock Microscope Slide Safety Follow usual lab safety rules. There are no major safety considerations in this experiment as the daphnia aren?t harmful and water above 40ËšC will not be used. Method To determine if temperature does have an effect on the daphnia, I intend to carry out the following experiment.
The experiment will involve measuring the cardiac activity of the daphnia at different temperatures, ranging from very cold (approx. 5 degrees Celsius) to quite warm (approx. 40 degrees Celsius). � A selection of similar sized/age Daphnia will be taken. � A variety of different temperatures of water will be set up, these temperatures will be kept constant whilst the daphnia are submersed in them. The temperatures will be set up by using ice to cool tap water down to lower temperatures and boiling water to heat it up. The temperature will be measured to within 0.1�C on a mercury thermometer to ensure accuracy. The temperatures will range from 10�C to approximately 40�C and it will be done at 5�C intervals. � The daphnia will be submersed in the water and left to equilibrate for 3 minutes, after this time one of the Daphnia will be removed and put onto a microscope slide, this will then be quickly put under the microscope. 1 � Under the microscope, the Daphnia will be observed for 20 seconds, this heart rate will be counted and recorded, this can the be multiplied by 3 to give a beats per minute. This way, the beats counted will be at as close temperature as possible, as they won?t have time to cool / warm significantly. � The experiment will be repeated twice for each temperature. Dependant variable: It is important to ensure that all variables are kept constant, allowing the experiment to be a fair one, to do this the following precautions should be taken: � The Daphnia used should be of a similar size and age to ensure that they react in the same way to the different temperatures. � The heartbeat should be counted as soon as possible after the Daphnia is placed under the microscope to ensure that the temperature it has equilibrated to remains as close as possible and is not affected by the light source of the microscope. � All of the Daphnia should be allowed the same amount of time to equilibrate to the temperatures, thus they all experience the same conditions and this makes the experiment more accurate. � The same person should always count the heartbeats to ensure that judgement errors do not affect the overall results. � Each daphnia should have the same transfer time from water to microscope. (If time exceeds 15 seconds, void that part of experiment and repeat.) � The temperature of the water needs to be monitored constantly to ensure that the results are being recorded at consistent temperatures. Independent variable � The temperature of the daphnia will be changed from 10˚C to 40˚C with 5˚C increments. This will be done by allowing the daphnia to acclimatise to different temperatures by putting their container in different temperatures of water. The results for experiment will each be repeated three times. � The heart rate of the daphnia will be counted by looking at them under a microscope with 100x magnification and taking heart beat for 20 seconds and multiplying this figure by 3 to give beats per minute. 2 Results === Temperature Heart rate of daphnia in beats per minute In ºC 1 2 3 Average 10 72 68 78 72.7 15 86 91 82 86.3 20 103 93 102 99.3 25 107 110 108 108.3 30 120 111 132 115.5 35 129 127 132 129.3 40 0 0 0 0 The underlined result for 30º C is clearly anomalous and therefore has not been included in the mean average beats per minute for that temperature. Interpretation of results ===== The graph shows a steep increase in heart rate as the temperature goes up, and from the graph, this looks linearly proportional. This is from 10ºC to 35ºC as the mean bpm goes from 72.7 to 129.3. The graph peaks at 35ºC where bpm is 129.3. At 40ºC all the heart rates fell to 0. Heart rate, along with most metabolisms in a living organism, is controlled by the action of enzymes. The hearts pacemaker, (sino-atrial node (san), also controls the Daphnia?s heart rate. The pacemaker sends out an electrical signal across the heart that makes it contract. Hormones and transmitters control the rate set by the pacemaker. The hormones communicate with the pacemaker in the membrane. The transmitter substance and hormone fit onto a protein molecule of the cell membrane, this causes the pacemaker to react. The theory is very similar to that of enzymes, more heat produces more kinetic energy and thus the hormones move more rapidly, this increases the chance that it will collide with the protein molecule on the cell membrane. Temperature, pH, enzyme concentration, substrate concentration and inhibitors affect enzymes. For a non-enzymic controlled reaction, the general rule is the higher the temperature, the faster the reaction. The same rule is true for a reaction catalysed by an enzyme, but only up to about 40˚C. This is shown between 10 and 35ºC. At 35ºC, the heart rate is at its fastest as this is when the enzymes are working at their fastest due to the large amount of kinetic energy the substrates have. Above 35ºC, the enzyme molecules begin to vibrate so violently that the delicate bonds that maintain tertiary and quaternary structure are broken, irreversibly changing the shape of the molecule. When this happens, the active site shape has changed and therefore an enzyme-substrate complex is no longer possible. This means that the enzymes and other protein structures controlling heart rate can no longer work. We then say it is denatured. This is shown at 40ºC. Although not all of the enzymes were denatured right after 35ºC, enough will have been denatured to slow down to process sufficiently to stop almost all metabolisms. Evaluation of practical work The experiment was carried out as accurately and safely as possible. Under school laboratory conditions and with the equipment available the experiment was flawed. There were problems in several aspects of the experiment; firstly the daphnia?s 3 heart rate is very fast most of the time, this gives the person observing a distinct problem in counting. We decided to count the heart rate for 20 seconds and then multiply that total by 3 to give beats per minute. This of course solved the problem of getting into very high unmanageable numbers that the observer would find difficult to cope with in a very short space of time. Unfortunately this in itself presented more problems. In a very small amount of time which twenty seconds is, the percentage error will be much greater than it would be overall in a much larger time frame as each error would be multiplied by three. If I was to repeat this experiment I would try a slightly larger time frame such as 30 seconds, this would reduces the percentage error whilst still keeping the counting to manageable figures. Another area in which error could have been introduced was using the microscope. The microscope requires a light source to function. Unfortunately the light source is also a source of heat, and whilst the daphnia are under it, the temperature they have been equilibrated to will rise, particularly the daphnia which were at very low temperatures will feel the effect of the light source. This problem was however minimised as the daphnia were only exposed to the microscope light for the twenty seconds need for counting and the five seconds needed to position the daphnia under then lens ? the microscope was focused correctly before commencing the experiment. The temperature of the water used was kept constant by topping up with hot / cold water, but when the daphnia were removed from the test tube, the ones at higher temperatures would have cooled faster than those at lower temperatures (above room temperature.) as there was a larger difference between them and their surroundings. Also, the stress of the changes of temperature and surrounding could have increased heart rate but this could not be avoided, as their heart rates could not have been taken in their natural environment as they would not normally be subjected to these temperatures. There was one clear anomalous result which was in experiment 3 at 30ºC. This result was higher than the others by at least 12 bpm and was equal to one of the bpm for the next temperature up. Despite the difficulties in this experiment, the overall results I gained were to a good degree of accuracy and were sufficiently conclusive to my original hypothesis.

An Investigation to Show the Effect of Temperature on Daphnia 8.9 of 10 on the basis of 3151 Review.