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have always been interested in sea animals and how they function. I had
previously learned about a “water flea” named daphnia in a biology class I took
in Turkey. Daphnia, (a genus of small planktonic
crustaceans) fascinated me due to their structure and the fact that I would be
able to observe their heart beats under a microscope is what inspired me to
come up with my research question. The single heart of daphnia can be seen
under a light microscope. The heart rate of the daphnia can go up to 300 beats
a minute. It can be observed in variety of conditions . I decided changing
water temperature and concentration of chemicals added to the water. Daphnia heart rate change results may not be
similar to the ones of humans, but this experiment provides a unique technique
for observing the effects of different chemicals on metabolic process.



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Daphnias are enclosed by a shell mostly
made of chitin. Daphnias have two sets of long, doubly branched antenna and a
single heart that could be monitored under the light microscope. Their heart rate can be monitored
and counted in different conditions – for example changing water temperature,
or changing the type and concentration of chemicals added to the water. I
decided to change two factors and observe their heartbeat under the microscope.


Experiment part 1

·       Research question: How does changing the temperature of water (0 ,10, 20
30 and 40 degrees) effect the heart rate of daphnia?

·       Independent variable: Temperature of water

·       Dependent variable: Number of heartbeats in one minute

·       Controlled variables: Type of liquid ( in this part of the experiment
the liquid should be kept the same since the effect of temperature is being
tested no other liquid should be involved as different chemicals will effect
the heart rate), amount of liquid (same amount of water should be used when
different temperatures are being tested so the daphnias are being exposed to
equal amount of the same liquid)



8-10 live daphnia

Water at different temperatures– 0 °C (in an
ice bath), 10 °C, 20 °C, 30 °C and 40 (regulate temperature with thermometer)

Low power microscope

Petri dish

Cotton wool piece

Pasteur pipette




1.     Place
small piece of wool in the middle of the petri dish

2.     Choose a
large Daphnia and  with the help of the pipette transfer it onto
the cotton wool fibres.

3.     add pond
water immediatly to the Petri dish until the animal is just covered by the

4.     Place the
Petri dish on the stage of a microscope and observe the animal under low power.
The beating heart will be located on the dorsal side above the gut. The heart
must be observed with transmitted light if it is to be properly visible.

5.     Use a
stopwatch to time 20 seconds, and equal it to how many heart beats it would
equal to in one minute.

For testing the effect of

Record the temperature of the water in the Petri dish.

Add pond water at a different temperature to the Petri dish.
Allow the Daphnia some time to cool down, keep checking
the temperature and adjust accordingly adding hot or cold water.

Record the heart rate again as in previous steps 

Plot a graph of mean frequency of heart beats per minute against



part 2

question: How does different concentrations of caffeine affect the heart rate
of daphnia?

variable: concentration of caffeine

variable: Number of heartbeats in one minute

variables: amount of caffeine given to daphnia, temperature of the chemical,
type of daphnia




 100 mg/L,
10 mg/L, 1 mg/L, 0.1 mg/L, 0.01 mg/L, and 0.001 mg/L
of caffeine

Microscope – low power, transmission

Petri dish

Pasteur pipette

Cotton wool(small piece)



Pour a small amount
(10 mL) of the solution to be tested into the Petri dish.
Pick up a daphnia and using the
pipette transfer it to the Petri dish.
Place the container under a
dissecting microscope and focus on the Daphnia so that
you can see the beating heart. Adjust the amount of water if the daphnia
moves around too much.
Count the number of heart beats
that occur in 20 seconds.
Record the number of heart
beats in your lab notebook.
Take at least three separate
heart rate measurements for each individual Daphnia and
calculate the average of the three measurements
Repeat the same procedure with
the different concentrations of caffeine which you will create by adding
spring water. Chlorine in water can kill the daphnia so make sure you use
spring water.
Graph your results. plot heart rate (y-axis) vs. log
concentration (x-axis)


Ethical issues

Daphnias are small organisms yet they are still
living so they deserve to be handled with respect..Animals must be returned to
the tank right after the experiment is done. Ethical issues should be addressed
and the animals should be safely returned to their habitat after observation is


Safety concerns

Daphnia can be kept in any watertight container
containing tap water that has been allowed to stand for a few days. Keeping a
few Daphnia is
not difficult but requires great care. Oxygen is essential for the survival of
daphnia. Make sure a large surface area of water is exposed to the air. Great caution should be taken when handling
these water fleas for their safety. Do not use tap water since chlorine can
kill them. Since you are working with live animals make sure they get enough
water and air for their survival.

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