Clarion University Science in Motion
Lab: Effect of Chemicals on Daphnia
Purpose: This lab is used to investigate the affect of over the counter drugs on Daphnia motility and heart rate.
Materials:
Motic Digital Compound Microscope
Laptop/Motic Software
Live Daphnia Culture
Depression Slides
Cover Slips
Droppers
Kimwipes
Diluted solutions of: Soda (with and without sugar, with and without caffeine)
Coffee (regular)
Cough Syrup Tea
Question:
What effect, if any, will caffeine, sugar, and cold medicines have on the motility and heart rate of Daphnia? Be
specific with each drug.
Procedure:
l. Set up microscope and laptop with Motic software.
2. Prepare a depression slide with a single daphnia.
3. Observe Daphnia allowing the organism a 3-5 minutes to acclimate to the microscope stage environment.
Pay particular attention to the Daphnia heart rate. If possible, take a heart rate count and record below in
Table 1.
4. Add one drop of solution containing soda with sugar. Allow the Daphnia to acclimate for 3-5 minutes.
Observe the movement and heart rate. If possible, take a heart rate count and record below in Table 1,
5. If there is time, complete steps 3 and 4 using other over the counter drugs, observing the Daphnia
behavior and heart rate, and recording the heart rate in Table l.
6. Clean up by placing Daphnia into a separate container your teacher provides for you. Rinse the slide and
cover slip, wipe dry and place in proper container.
Analysis of Results:
1. Share your data with other members in your class
2. What affect did each chemical have on Daphnia heart rate and motility?
3. Do you think that these chemicals have similar affects on humans? Why or why not?
Table 1: Effect of Chemicals on Daphnia
All heart rates are taken for ________ seconds,
Resting Heart
Rate
Caffeine
Sugar
Caffeine and
Sugar
Cold Medicine
Average
Average
Average
Average
Average
Additional Data: Use the table below if you have additional chemicals.
Write the name of the chemical in the top box of the column, then
Place your data as well as your classmate's data below the column.
Average
Average
Average
Average
Average
Effect of Chemicals on Daphnia
Teacher's Notes
Preparation of Materials:
1. Daphnia can be order a week in advance from Carolina. It is not recommended to do this lab on a
Monday, as Daphnia are shipped overnight.
2. Once materials are purchased, dilutions can be made within 20 minutes. Products containing
chemicals may be varied, depending on your lesson goals, and availability of materials. You may also
add chemicals such as nicotine and alcohol.
3. Prepare a 5% dilution with distilled or tap water for each substance used. Label containers, and
provide a dropper for each.
4. It may be helpful if you show the students a Diagram of Daphnia, specifically locating the heart.
5. Depending on student grade and ability level, as well as time, you may wish to prepare the slides
and have them ready to view.
6. If time is limited you may wish to assign one chemical solution to each lab group.
Initial Questions:
You may have students prepare a formal or informal hypothesis of the affects of these drugs on
motility and heart rate of Daphnia. Initial questions, and lesson objectives may vary depending on ability
level of students and course objectives.
Answers to Questions:
1.
Sharing data is recommended with class periods too brief to complete each chemical
observation.
2. Answers will vary. Caffeine and sugar generally increase mobility and heart rate, while cold
medicines, and alcohol decrease mobility and heart rate.
3.
Answers will vary. Most students will make the connection and infer humans to have similar
results when exposed to these chemicals.
Taking the Investigation a Step Further:
1. You may extend the investigation by introducing Hydra, as another separate organism to observe
and/or observing Hydra and Daphnia together.
C U L T U R I N G
DAPHNIA
Using Daphnia for bioassays requires advance planning to make sure that you have a healthy,
nonstressed population from which to choose your test organisms. If you order cultures through the
mail, be sure to allow sufficient time for shipping of replacement cultures in case the original ones
arrive in poor condition. After the Daphnia arrive and have stabilized at room temperature, lower the
shipping jar into an aquarium or gallon jar containing unchlorinated water (see Culture Water, below).
Plan on maintaining a healthy culture for at least a week or two before using the organisms for
bioassay experiments. EPA recommends not using a culture for bioassays if more than 20% of the
Daphnia die during the two days preceding the test.
Life Cycles of Daphnia
Daphnia typically live 40 to 56 days, varying according to species and environmental con ditions. Each
female has a brood chamber holding 6-10 eggs, which turn into embryos and are released within a few
days. Juveniles reach sexual maturity in 6 to 10 days. A healthy population of Daphnia consists mostly
of females that have been produced asexually. The culture can become stressed if the population
density gets too high, by a food shortage, poor water quality, or extreme temperatures. Under stressfu l
conditions, Daphnia produce more male embryos and begin to reproduce sexually. The resulting
resting eggs will not hatch until they have gone through a certain sequence of environmental changes,
including several freeze/thaw cycles. Therefore, if you want to maintain a steady supply of Daphnia in
your lab, you will need to avoid the stressful conditions that lead to sexual reproduction.
Culture Water
Daphnia are quite sensitive to the chemistry of the water in which they live. In order to provide
standardized culture water, professional scientists start with distilled water and add essential minerals
and nutrients (see Table A.2). The problem with this approach in schools is that you may not have
access to distilled water of sufficient purity. Supermarket-grade distilled or deionized water may contain
trace-level contaminants at concentrations high enough to be detrimental to populations of Daphnia. An
alternate possibility is to use unchlorinated water such as bottled spring water or water from a local
well, spring, stream, or lake. It also is possible to start with chlorinated tap water and either let it sit long
enough for the chlorine to evaporate, or treat it with activated charcoal or one of the products sold for
dechlorination of water to be used in aquaria.
TABLE A.2
Recipe for Synthetic Culture W ater for Daphnia
Compound
NaHCO 3
CaSO 4 •2H 2 O
MgSO 4
KCl
Concentration (g/L)
0.192
0.120
0.120
0.008