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Investigating the effects of temperature on the heart rate of Daphnia.

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Investigating the effects of temperature on the heart rate of Daphnia. Introduction Daphnia is the name of a group of small, aquatic crustaceans commonly called 'water flies'. Because their exoskeletons are clear it is possible to watch daphnia hearts without cutting them open. This also allows the changes in daphnia heart rate to be studied quite easily. As temperature has been chosen as a variable, it must be considered that daphnia are cold-blooded animals, they do not thermo regulate. This means that their body temperature is the same as the water they are floating in. Daphnia Source: www.bioweb.lu/sapro/Daphnia.gif Anatomy of daphnia: 1. Antenna, used for swimming and sensing the environment. Also they are used for gathering food. 2. Eye controlled by muscles with nerve connections to the brain 3. A heart that pushes clear fluid around the body 4. A brood pouch for incubating young that hatch from yolk filled eggs 5. An intestine where ground up food particles are digested 6. Undigested material is eliminated out of the anus Daphnia live in water and have large antenna [as seen in diagram], these are used to make jumpy movements - hence the name 'water flies'. As daphnia are cold-blooded organisms, so the temperature of their environment should affect the rate of their metabolism. The prediction is; as the temperature of the water that the daphnia are in rises, so will the heart rate. ...read more.


2nd 10 seconds 3rd 10 seconds Total heart beats/ minute 1 15 21 27 189 2 10 21 34 195 3 11 24 33 204 Table 2. Results for 18oC. Daphnia No. of heart beats / 10 sec. 2nd 10 seconds 3rd 10 seconds Total heart beats / minute 1 20 33 37 270 2 29 32 30 273 3 26 35 33 282 Table 3. Results for 35oC. Daphnia No. of heart beats /10 sec. 2nd 10 seconds 3rd 10 seconds Total heart beats /minute 1 52 41 39 396 2 37 42 34 339 3 33 39 36 324 There are no results for 40oC as all the daphnia died. Evaluation: Conducting this experiment demonstrates that by using a fluctuation in temperatures to which the daphnia are in either slows the heart rate down or increases it. By comparing the heart rates of three daphnia in each temperature scale, you can tell whether temperature is a stimulant, depressant, or has no effect on the heart rate. The physiologic mechanisms, by which the change in heart rate is brought about is by chemical reactions that occur in the cells of daphnia, which are dependant on certain enzymes, or proteins to help reactions proceed. As we increased the temperature of the water, the metabolism increased as well, because chemical reactions occur faster at higher temperatures. ...read more.


As the enzyme had been denatured by the heat, leaving the daphnia to return to room temperature had no effect, the enzyme had lost its tertiary shape and cannot work again. What is evident from this investigation is that daphnia can withstand a wide range in temperatures in which they are situated in from 0oC to 35oC. Overall I think the results are fairly accurate, but there will always be some inaccuracy in the results because of the 'human factor', such as a delay in observing the daphnia under the microscope due to the fact it was difficult to focus, causing a rise in temperature from the light, also the use of a clicker counter would have helped a lot in recording the heart beats. Plus also daphnia do not always respond and cooperate, as they should. Possibly if we had made sure that all the daphnia tested were all the same size, in good health and that none had any eggs in their brood pouch could have made the results more precise. Other significant investigations into factors that could affect daphnia's heart rate and their general behaviour would be interesting experiments to do. I would suggest using further variables such as solutions of caffeine or alcohol, or possibly as daphnia are fresh water organisms, saline solutions or changes in pH should also produce an interesting investigation. This has been a comprehensive experiment that demonstrates the association between temperature and the rate of metabolism in daphnia. ...read more.

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