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The Effect of Temperature on the Q10 of Daphnia

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The Effect of Temperature on the Q10 of Daphnia


The purpose of this experiment is to find the effect of temperature on
the heart rate of Daphnia, and then to calculate the Q10 of Daphnia.
We are interested in finding if the external temperature affects the Q10,
thus the question to be answered in this lab is: Does the external
temperature effect the Q10 of Daphnia? The answer to this will be
found by examining Daphnia at three different temperatures: 4oC, 20oC
and 30oC. By measuring the heart rate of these organisms at these
different temperatures, the Q10 can be calculated. The Q10 will be
calculated at the cold temperature and the warm temperature relative
to the room temperature.

Q10 is the multiple by which a particular enzymatic reaction or
overall metabolic process increases with every 10oC increase in body
temperature (1). Usually the rates of most enzyme- mediated reactions
increase by a factor of 2-3 for every 10oC increase in temperature
(1). The basic formula used to calculate Q10 is dividing the heart
rate at room temperature by either the heart rate at cold temperature
or warm temperature.

Daphnia, also known as water fleas, are small crustaceans that live in
fresh water. They serve as an important source of food for fish and
other aquatic organisms (3). Daphnia are excellent organisms to use in
experiments because they are sensitive to change, are simple and are
inexpensive (3). They respond quickly to a change in environment
because they are such tiny organisms (3). They are often used to check
the acidty of a chemical compound that may be found in water(3).
Daphnia are transparent so it is easy to observe their heart rate
under a microscope.

All organisms can be placed into two distinct groups: ectotherms or
endotherms. Ectotherms are those organisms that have body temperatures
close to the environmental temperature. Therefore, the body
temperature of these species depends on their environment. Examples of
ectotherms are fish and reptiles (1). These creatures tend to have a
low metabolic rate and the amount of heat they generate is too small
to have much effect on the overall body temperature. These animals
control their body temperature by behavior- they warm up by moving
into sun, cool down by moving into shade or water. In contrast,
endotherms are creatures which use metabolic heat to keep their body
temperature warmer than their surroundings. By increasing metabolic
rate, these creatures can generate enough heat to keep their body
warmer than their environment. Examples of endotherms would be
mammals, birds and insects (1). An advantage of being an endotherm is
having a high and stable body temperature as well as increased levels
of aerobic metabolism (cellular respiration.) This enables animals to
maintain stable body temperature in the face of environmental
temperature fluctuations that are generally more severe in aquatic
habitats (1). A disadvantage of being an endotherm is the increased
need for food. Endotherms generally need more food than ecotherms, and
this could be a disadvantage if food supplies are limited.

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

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.


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

Table 1: The Effect of Temperature on the Heart Rate of Daphnia (rough

Temperature (oC)

Heart Rate (beats/min)

Trial 1

Trial 2

Trial 3

Room (20)







Cold (4)









Warm (30)







Table 2: The Effect of Temperature on the Heart Rate of Daphnia.

*Note: results in each trial were averaged from class’s data.

Temperature (oC)

Heart Rate (beats per minute)

Trial 1

Trial 2

Trial 3


Cold (4)










Room Temp. (20)










Warm (30)










Table 3: The Effect of Temperature on the Q10 of Daphnia

Temperature (oC)








Calculations: (Q10 values calculated relative to room temperature.)

Q10 cold = Heart rate at room temperature/Heart rate at cold

= 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:



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.


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


1. Campbell, Neil A. and Jane B. Reece, 2002. Biology-6th edition:
San Francisco: Benjamin Cummings. Pp

2. SBI4U Lab Manual 2004-2005. Evolution and the Nature of Science-
Part 1. Author. Ms. Davis

3. Environmental Inquiry [Online] Available, October 9,

How to Cite this Page

MLA Citation:
"The Effect of Temperature on the Q10 of Daphnia." 16 Apr 2014

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