Lab 1: Investigation of the effect of drugs on Daphnia Magna
Background
A Daphnia is a tiny crustacean that has a clear
exoskeleton. Daphnia is a keystone species in
ponds and lakes. They are typically primary
consumers that feed on algae and are
themselves the main food source for small fish.
Because of their pivotal position in food webs,
they are used as an indicator species to assess
the response of ecosystems to environmental
change – if the population of Daphnia are
adversely affected, it’s a bad sign of things to
come for the ecosystem.1
Like all arthropods, its heart is on its back. This
makes Daphnia an ideal model organism for
studying the physiology of the heart, as it can
be seen beating beneath the transparent
Figure 1: Daphnia magna. Arrows indicate the
carapace under the compound light
walls of the heart. The white space beneath the
microscope. In female Daphnia, it is often
heart is an empty brood pouch for eggs.
possible to see fertilized eggs, which are carried
on the back in a cavity behind the heart. There are two species of Daphnia: Daphnia pulex is smaller and
usually utilized in feeding, behavior, and reproduction experiments; Daphnia magna is larger and is the
species usually used for heart rate studies, because its heart is larger and more visible.
As in other animals, the heart rate of Daphnia is under the control of the nervous system. Though
Daphnia lack a true endocrine system, some specialized neurons secrete neurohormones into the
circulatory system that send chemical messages throughout the body of the organism. Chemicals that
affect these communication systems may have an effect on the heart rate as well.
In this lab you will investigate the effects of ethyl alcohol and caffeine on the heart rate of Daphnia.
Caffeine is commonly referred to a as a stimulant and alcohol as a depressant, but in fact their effects on
the heart rate are more complex. At the dose typically consumed in a cup of coffee, caffeine causes a
moderate reduction of the resting heart rate; it is only at higher doses that its stimulating effect on the
heart rate can be observed. Alcohol is a stimulant at low doses, but depresses the heart rate as
intoxication levels increase. A change in the heart rate of humans, however, may or may not be a
predictor of the same effect in Daphnia. Though we are both animals, humans and Daphnia are in
different phyla and the organization of their nervous and circulatory systems differs substantially.
Assessment
This lab is divided into two parts:
1. Design: Materials, Method, Diagram, Safety & Ethics, Works Cited (Due________ to Turn-it-in)
2. Evaluation: Conclusion and Evaluation (Due ________________ to Turn-it-in)
1
Clare, John. “Daphnia: An Aquarist’s Guide.” Caudata. Accessed June 2015. www.caudata.org/daphnia.
Materials available
 Daphnia magna
 3-mL pipettes
 deep well slides
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bottled spring water
light microscope
cotton balls
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ethanol (5%, 10%)
caffeine (0.5%, 2%)
culture jars
Method
Measuring the heart rate of Daphnia is a time intensive activity, so we will collect data as a class for this
lab. This means the basic design of this lab has been determined by your instructor and will be
described below. Your task is to develop and write your own methods section that will help the class
achieve the design outlined below. The most comprehensive, clearly written method will be selected for
the class to follow during our next lab recitation.
The Design

The independent variable is drug exposure. Daphnia will be exposed to one of five solutions: 5%
or 10% ethanol, 0.5% or 2% caffeine, or a control solution (spring water).

The dependent variable is heart rate, measured in bpm. A single Daphnia will be viewed under
the microscope and its heart rate will be recorded at 2-minute intervals for 20 minutes total.
The first 8 minutes, the Daphnia’s heart rate will be recorded while it is in the culture water
from the tank, in order to establish a baseline heart rate. At minute 8, the culture water will be
replaced with the exposure solution for the remainder of the time.

Each set of lab partners will contribute one trial (one Daphnia) to the class data.

Care should be taken to provide ethical care to the Daphnia. Stress that may affect heart rate
should be avoided.
Protocols for Working with Daphnia
You will need to do some research about proper lab technique for working with Daphnia. Consult the
sources below as you craft your method, and remember to clearly cite them in your Works Cited.
Source 1: Nuffield Foundation Practical Biology
http://www.nuffieldfoundation.org/practical-biology/investigating-factors-affecting-heart-rate-daphnia
Source 2: Carolina Biological (video)
http://www.carolina.com/teacher-resources/Video/daphnia-heart-rate-experiment-video/tr11197.tr
Source 3: American Biology Teacher
http://web.as.uky.edu/Biology/faculty/cooper/ABLE/Daphnia_Concentration_Paper.pdf
Blank space for notes about method as you view the sources given above
Rough Draft of your Method
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Diagram
Sketch a labeled diagram that depicts a Daphnia prepared for viewing on a slide. You will need to
recreate this in Google Drawings for the diagram in your lab report.
Safety and Ethics
Consider potential safety hazards to yourself and ethical care of Daphnia. Refer to sources as needed.
Safety or ethical concern
How you could address it
Qualitative Data
Use this space to record the observations you make during your experiment. Consider the following:
 Note any interesting anatomical features of your Daphnia, such as the presence or absence of
eggs in the brood pouch
 Describe the behavior of the Daphnia before and after exposure
 Take not of any irregularities in the heart beat
 DO NOT write, “the heart is beating very fast.” That will be addressed by your quantitative data!
 After returning the Daphnia to the culture jar you might observe it for a few minutes and
describe its behavior
Raw Data
Table 1: Heart rate of a single Daphnia over 20 minutes, with exposure to ________________________
Drug
Treatment
Time
(min)
Water
0
Water
2
Water
4
Water
6
Water
8
Drug
10
Drug
12
Drug
14
Drug
16
Drug
18
Drug
20
Heart Rate
(bpm)
Heart Rate
(percent of initial)
Sample calculation
100
Formula:
Example:
Data Processing
Calculations
The Daphnia’s raw heart rates will naturally vary, which will obscure any trends in how the drugs affect
them. To highlight the patterns in the heart rate and make it easier to aggregate the data, we will
calculate the heart rates as a percent of their initial value:
𝐻𝑒𝑎𝑟𝑡 𝑟𝑎𝑡𝑒 (% 𝑜𝑓 𝑖𝑛𝑖𝑡𝑖𝑎𝑙) 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑥 =
𝐻𝑒𝑎𝑟𝑡 𝑟𝑎𝑡𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 𝑥
𝑥 100%
𝐻𝑒𝑎𝑟𝑡 𝑟𝑎𝑡𝑒 𝑎𝑡 𝑡𝑖𝑚𝑒 0
This calculation is similar to the percent change, but avoids any messiness having to do with positive and
negative signs. If the heart rate is exactly the same as the initial heart rate, it will be calculated as 100%
(the full value of the initial reading). An increase in heart rate will yield values greater than 100%, and a
decrease in heart rate will result in values less than 100%.
Use your calculator to calculate the heart rate as a percent of the initial value and fill in Table 1. Show a
sample calculation.
Graph
The excel spreadsheet will plot separate graphs showing the class data for alcohol and ethanol. Your
instructor will print these graphs for you to paste here.
Conclusion
Write clear, concise paragraphs that address the following questions.
1. Closely read the data in your graph:
a. Do these drugs affect the heart rate? If so, how?
b. If the drug affected the heart rate, how long did it take for the effects to be measurable?
Did the effects persist or wear off over time?
c. What is the minimum dose to see an effect of the drug, and how sure are you? (Think
about the scope of your conclusion and how it is limited by our experimental design.)
d. Pay attention to the error bars. Did one drug or dose produced noticeably more varied
effects than the other?
2. Compare and contrast your results with those of Source 3 (see Methods). Do your findings,
confirm, refute, expand, or refine their conclusions?
Evaluation
Use this graphic organizer to plan; each row is one paragraph. Go to reference material for a review of
the difference between systematic, random, and practical and procedural errors.
Limitation
Describe:
Type of error (check):
 Systematic (skew higher)
 Systematic (skew lower)
 Random
 Not applicable
Describe:
Type of error (check):
 Systematic (skew higher)
 Systematic (skew lower)
 Random
 Not applicable
Describe:
Type of error (check):
 Systematic (skew higher)
 Systematic (skew lower)
 Random
 Not applicable
Explain how it affected the data
Suggest a specific improvement