The effect of temperature on the Heartrate and Respiration of Daphnia

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The effect of temperature on the Heart rate and
Respiration of Daphnia
Introduction
A lot of research has been conducted on the influence of temperature on physiological
processes in animal models, results typically show an increase in the process rate with
increasing temperature. The aim of this study is to further investigate the effects of
temperature on heart rate for action potential generation, and oxygen consumption in
Daphnia.
Understanding the effects of temperature on physiological processes is of great value. As a
temperature reduced from its optimum results in a decreased rate of metabolic processes,
this may be used to improve neurological outcomes in patients who have suffered a brain
trauma such as stroke. Target temperature management (TTM) involves inducing
hypothermia in a patient to decrease metabolic rate and re-establish appropriate oxygen
levels. Many investigations show that in patients with perinatal asphyxia, TTM resulted in
improved neurological outcomes (CSZ Medical, 2015). Evidence also suggests that TTM may
be used to treat neurological injuries, such as those seen in stroke patients. One piece of
research showed that moderate TTM resulted in an average reduction of 44% of the
magnitude of the infarction and improved neurological outcome of patients who suffered
an Ischemic stroke (Andresen et al., 2016).
This presents the importance of research regarding the effects of temperature on metabolic
processes.
As ethical reasons prohibit the use of vertebrate animals in this study it was performed on
Daphnia. Daphnia, also known as `water-flea', are freshwater invertebrate animals which
respire aerobically, they have an optimum temperature of 18-22 0 C but can survive in
temperatures between 2-300 C (Goss and Bunting, 1983). Daphnia's internal organs are
easily seen under a light microscope due to their transparency, their heart is also an
excitable tissue which is dependent on oxidative metabolism and is stimulated by action
potentials. As Daphnia is an ectoderm, it's internal body temperature can be changed by
changing its environment, making it a suitable model for investigating the effects of
temperature on heart rate and rate of oxygen consumption.
The Q10 values for heart rate and OCR from this experiment will be calculated and compared
to those deduced in previous experiments. Q10 is the ratio between two reaction rates or a
physiological process at two temperatures which are 100 C apart, it is used to mathematically
describe temperature sensitivity. The Q10 for metabolic processes are usually 2-3, this is the
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The activation energy for heart rate and OCR will also
be produced by plotting an Arrhenius Plot of Ln(k) (rate process) against 1/T. The slope of
the line of best fit on this graph is equal to -Ea/R.
Hypothesis:
1) There will be a significant increase in heart rate with increasing water temperature.
2) There will be a significant increase in the rate of oxygen consumption with increasing
water temperature.…read more

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A thermometer was then placed in the chamber
to monitor the temperature and the Daphnia were positioned so that the heart could be
viewed and the rate recorded. Different Daphnia were used to calculate heart rate for each
of the 5 temperatures.
The equipment to determine oxygen consumption rate was set up using an O2 electrode to
measure the concentration of oxygen (O2(aq)) in the fluid of the closed system. The electrode
contained 4ml of oxygen rich pond water.…read more

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C. During this time a different individual recorded
to obtain 5 results for heart rate at ~100
the concentration of oxygen displayed on the voltmeter every 60 seconds for 5 minutes.
C, ~200
This was then repeated to deduce heart rate and oxygen concentrations at ~150 C,
~250 C and ~300
C by preparing and maintaining the temperature using the equation
previously described with hot water and ice for each new temperature.…read more

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T was then calculated by converting the temperature in Degrees Celsius to Kelvin
C = 283K), then diving 1 by the temperature (eg.
by addition of 273. (eg. 100
1/283=353.4x10-5 ).
Ln(heart rate) was then calculated and plotted against 1/Temperature to produce an
Arrhenius Plot (see figure 3).
As the slope of the Arrhenius Plot is equal to -Ea/R,
this was then used to calculate
the activation energy of this process.…read more

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Example: OCR at 100 C= 572, OCR at 200
C= 1150)
Q10 = 1150 / 572 = 2.01
As there was a variation between Q10 values at different temperatures, the mean
Q10 value was also calculated from these results (see table 2).
Activation Energy Calculations:
Ln(OCR) was then calculated and plotted against 1/Temperature to produce an
Arrhenius Plot (see figure 4), using the 1/T values previously obtained.…read more

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Pearsons test performed on Prism produced a correlation coefficient value of r=0.987, and
p=0.0007).
The results show an increase in mean OCR with increasing temperature. Statistical analysis
tests showed a significant positive association between temperature and mean OCR of
Daphnia. The SEM for mean OCR also increases with temperature increase. This can be seen
in figure 2.…read more

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Mean: 1.78
(Table 1 shows the temperatures from which the mean Q10 Value for Heart Rate were
deduced. SD±0.036 and SEM±0.021).
The Q10 value for Oxygen Consumption Rate was found to increase from 2.01 to 3.25
between the temperature intervals of 10-200 C and 15-250 C. The mean Q10 value calculated
for OCR in Daphnia was found to be 2.63. This can be seen in table 2.
Table 2
C
Temperature Intervals / 0 Q10 Value
10 ­ 20 2.01
15 ­ 25 3.…read more

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Figure 3 gives a visual representation of the association between the mean Ln heart rates
and 1/T. The Pearsons test performed on Prism produced a correlation coefficient value of
r=-0.999, and p=<0.0001. The gradient of the graph was found to be -5012 ± 127.9).
A significant linear associations was found between mean ln OCR and 1/temperature, as
seen in figure 4.
Figure 4
(Figure 4 gives a visual representation of the association between the mean Ln OCR and 1/T.…read more

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Discussion
For the one-tailed Pearsons test it was assumed that the data are parametric for both heart
rate and OCR. The results for mean heart rate against temperature and OCR against
temperature show a strong significantly positive relationship, supported by the Pearsons
statistical test (heart rate: r=0.987, p=0.0007) (for OCR: r=0.918, p=0.0409), therefore
hypothesis 1 and hypothesis 2 have been accepted and their retrospective null hypothesis
rejected.
As Daphnia are ectotherms increasing the temperature of the water (their external
environment) increases their internal body temperature.…read more

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