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My hypothesis is that with an increase in temperature a Daphnia's heart rate willincrease.

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Introduction

HEFC BIOLOGICAL SCIENCE - UNIT 2 Joseph Colledge ASSESSED PRACTICAL VARIATION OF DAPHNIA HEART BEAT WITH TEMPERATURE a) My hypothesis is that with an increase in temperature a Daphnia's heart rate will increase, likewise with a reduction in temperature the heart rate will decrease. This is due to the Daphnia being an ectothermic organism, so its body heat is determined by its environment, namely that their body temperature is the same as the water they are floating in. Thereby having a direct effect on its metabolic rate. b) A Daphnia was taken via a teat pipette from a beaker of room temperature water (Measured at 20?C) and placed onto a cavity slide, this was then placed under a microscope. The heart was then located via the use of diagrams and confirmation sought by a person who had previously carried out the experiment. It was then decided that to get the most accurate results a group of 2 people would be most efficient, one person would be responsible for counting the beats per minute whilst the other would govern the time. ...read more.

Middle

This was to be carried out at 5 different temperatures and the average bpm results documented. c) Table to show how temperature effects the heart rate of a Daphnia Temperature ?C Heartbeats Per Minute 2 100 10 135 16 180 20 210 32 480 Joseph Colledge d) The results show that due to the Daphnia being Ectothermic (cold-blooded) and therefore not able to thermo-regulate itself, the temperature of the water in which it habituates has a direct effect on its heart rate. The reason for this is that the chemical reactions that occur in the Daphnia are dependent on certain enzymes, or proteins to help them proceed. As the temperature of the water is increased, the metabolism of the Daphnia increases also; this is due to chemical reactions occurring faster at higher temperatures due to an increase in kinetic energy. As a consequence of this increase, the heart has to beat faster as more Carbon Dioxide is produced from the cells during respiration. This can cause acidic conditions which will eventually denature enzymes, so more oxygen needs to circulated which is why the heart speeds up. ...read more.

Conclusion

It would also greatly change the amount of bpm if the Daphnia were pregnant and that was very hard to determine. Another would be the amount of stress, which the Daphnia is placed under during the experiment. The final error is the fact that in some cases the Daphnia being used would die and another used to carry out the remainder of the experiment, which would invalidate previous heart rates. f) To improve the experiment I would suggest that natural light was used for the microscopes rather than lamps to reduce heat. Another way to improve it would be to film the beats of the heart with a video camera then play them back in slow motion to get a more accurate count. Getting a person who is experienced with them to say whether it's a male/female would give more accurate results also. Also if a Daphnia dies during the experiment it would be more accurate to just start again rather than continuing with the same results from the previous one. ...read more.

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