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The Heart Rate of the Daphnia

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The Heart Rate of the Daphnia

My aim is to investigate the heart rate of the daphnia whilst the
temperature of the surrounding environment is the variable to be
changed. This variable will increase or decrease the heart rate. I
will need to do some research and preliminary work before I choose my
temperature and the way I carry out the process efficiently and
effectively.

Prediction

I predict during the investigation the heart rate of the daphnia will
increase as the surrounding temperature increases and vice-versa. But
at a certain point the daphnia will stop responding if the temperature
decrease or increases too much.

Temperature (oC)

Heart

Rate

(bpm)

[IMAGE]

I also predict that if the temperature doubles so should the heart
rate of the daphnia. For example if at 10oC the heart rate is 50 then
at 20oC the heart rate should be 100.

Scientific Knowledge

The daphnia adapts to its surroundings because it is a cold blooded
animal and the daphnia doesn't thermo regulate, meaning that there
body temperature is the same as the water they are existing in. The
daphnia' internal body reactions increase as the temperature
increases; this causes the heart to beat faster at higher
temperatures. The heart rate increases because as the internal
operations of a daphnia speed up the parts of the daphnia require
oxygen. So, the heart beats quicker to provide oxygen to the cells as
the metabolism increases. Also the heart beats slower when the
temperature decreases because the chemical reactions have slowed down
which decreases the amount of oxygen required. 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 35ËšC. 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 30ËšC, 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. Although not all of the
enzymes are denatured right after 30ËšC, enough will have been
denatured to slow down to process sufficiently to stop almost all
metabolisms.

Variable

The main variable of my investigation is temperature. I will have to
make sure that I correctly measure and sustain temperature levels
required to gain efficient and reliable results.

Some other variables I will need to control and are stated below: -

o The daphnia it self is quite delicate and could die easily.

o The daphnia moves a lot on the microscope so it will be a task to
control this movement.

o The lab temperature could also effect the investigation.

o The minimum and maximum temperatures that a daphnia can live in will
have to be decided.

o I might have to change the daphnia, which could affect the results
because the new daphnia's metabolism might work faster or slower than
the original daphnia.

Equipment

o Daphnia

o Microscope

o Cover slip

o Beaker

o Water

o Thermometer

o Pipette

o Counting instrument

o Bunsen burner

o Stop clock

Preliminary Work

We did a period when we did a trial with the daphnia. During this
preliminary work I noticed the temperatures that the daphnia can
survive and other factors, which will effect my actual investigation.
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. The cover slip
on the microscope killed the daphnia and also it was very hard to
count the heartbeat because of how fast it beats. To tackle this
problem I won't use a cover slip and I will use a counting instrument
to count the data. The problems encountered during the preliminary
work have now been addressed and the following method has accounted
for those problems accordingly.

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. 35 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 0C on a mercury thermometer to ensure accuracy. The
temperatures will range from 5 0C to approximately 35 0C and it will
be done at 5 0C intervals.The daphnia will be submersed in the water
and left to equilibrate, after few minutes one of the Daphnia will be
removed and put onto a microscope slide, this will then be quickly put
under the microscope. 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 four times for each temperature.

Measurements

The measurements will be between 5oc - 35oc going up in 5oc and I will
do four trials for each temperature and do an average to increase
reliability of the data. I am choosing these temperatures because I
have learnt from my preliminary work that the temperatures at the
extreme of the temperatures I've chosen are not suitable for the
daphnia to survive.

Results

Temp oC

Heartbeat after 20 (bpm)

Heartbeat after 1 min

Trial 1

5

55

165

Trial 2

5

45

135

Trial 3

5

49

147

Trial 4

5

53

159

Average

Average

50.5

151.5

Trial 1

10

61

183

Trial 2

10

67

201

Trial 3

10

63

189

Trial 4

10

59

177

Average

Average

62.5

187.5

Trial 1

15

69

207

Trial 2

15

78

234

Trial 3

15

72

216

Trial 4

15

75

225

Average

Average

73.5

220.5

Trial 1

20

72

216

Trial 2

20

75

225

Trial 3

20

79

237

Trial 4

20

80

240

Average

Average

76.5

229.5

Trial 1

25

81

243

Trial 2

25

94

282

Trial 3

25

93

279

Trial 4

25

89

267

Average

Average

89.25

267.75

Trial 1

30

54

162

Trial 2

30

67

201

Trial 3

30

63

189

Trial 4

30

70

210

Average

Average

63.5

190.5

Trial 1

35

45

135

Trial 2

35

50

150

Trial 3

35

53

159

Trial 4

35

61

183

Average

Average

52.25

156.75

My results show that as the temperature increases, so does the heart
rate of the daphnia. However after 25oc the heart rate of the daphnia
decreases.

[IMAGE]



Trends and Patterns
===================

The graph gradually increases as the temperature increases as I
predicted controversially the temperature decreases at a certain point
as I also mentioned in my prediction. The point at which the
temperature decreases is at 25oc. All this is due to the increase in
heat energy. The daphnia adapts to its surroundings because it is a
cold blooded animal and the daphnia doesn't thermo regulate, meaning
that there body temperature is the same as the water they are existing
in. The daphnia' internal body reactions increase as the temperature
increases; this causes the heart to beat faster at higher
temperatures. The heart rate increases because as the internal
operations of a daphnia speed up the parts of the daphnia require
oxygen. So, the heart beats quicker to provide oxygen to the cells as
the metabolism increases.

The temperature starts too decrease at 25oc because at 25 degrees
Celsius, the enzymes start to break down, and the chemical reactions
can no longer occur, so metabolism slows down causing the Daphnia'
heartrate to decrease which will eventually terminate.

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"The Heart Rate of the Daphnia." 123HelpMe.com. 16 Apr 2014
    <http://www.123HelpMe.com/view.asp?id=123089>.




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