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Date:
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Circulatory System Worksheet
Directions:
Observation of the Heart of Daphnia
 Obtain a vial of Daphnia. Measure and record the temperature
of the water in the vial.
 Place a drop of the Daphnia onto a slide, and put on a cover
slip. Place the slide on the microscope, under the scanning
objective.
 Focus on the reddish pulsating object in the thorax of the
Daphnia. This is the heart. Increase the magnification as high
as possible, and observe the flow of blood. Record the number
of heartbeats in a minute.
 Add a drop of cold water to the slide and observe if the heart
rate changes. Observe for eight minutes, recording the rate
every two minutes.
 Add a drop of warm water to the slide, preferable warmer than
room temperature but not boiling. Record the temperature, then
repeat the observation of the heart rate under the microscope.
 Based on your observations, write down what you infer about
the effects of temperature on the heart.
Identifying Heart Sounds
 Obtain a stethoscope and wipe the ear pieces with an alcohol
swab. Place the ear pieces in your ears.
 Place the bell of the stethoscope on your partner’s chest, and
listen for the heartbeat. It may sound like “lub dub”
 Identify the first sound (the lub), which signals contraction of the
heart (systole). How long is the interval between the first sound
and the second sound (the dub), which signals relaxation of the
heart (diastole).
 Time the interval between the second sound and the next first
sound. After five of these intervals, estimate the average time
the heart is at rest in a minute, and the average time the heart
is in contraction in a single minute.
Observation of Daphnia:
1. Describe what the heart looks like.
2. Write the number of beats per minute.
3. What happened to the heartbeat when you added the cold water
to the Daphnia?
4. What happened to the heartbeat when you added the hot water to
the Daphnia?
5. Why do you think this is?
Observing Heart Sounds:
6. Which sound is louder, the first or the second sound in a heart
beat?
7. Why do you think that is?
8. Write the number of heartbeats per minute:
9. Time between first and second sound:
1st Trial:
2nd Trial:
3rd Trial:
4th Trial;
5th Trial:
Average:
10. Amount of time the heart is contracting in one minute (hint: how
many heartbeats are in one minute.