Science project

The Effect of Caffeine on the Heart Rate of Daphnia Magna

Difficulty of Project



Live Daphnia cultures can be ordered online for anywhere from $3-$30, or be purchased from your local fish store. Live yeast can be used as food, for $2 a packet. Distilled water- or tap water left out for 48 hours- is also inexpensive. While laboratory grade caffeine is both expensive and dangerous, any household chemical can be used cheaply- coffee works just fine, as does any household food product or chemical that might have an effect on heart rate.

TOTAL: $10-50.
Safety Issues

Care should be taken when mixing solutions. All safety hazards and guidelines that apply to any chemicals used should be followed. 

Material Availability 

Almost all high school labs will have access to microscopes, well slides and the appropriate glassware. Daphia must be purchased from an aquarium or online, and it’s a good idea to start a living culture, which is easy enough. Any other supplies can be purchased at any grocery store 

Approximate Time Required to Complete the Project  

Gathering the materials is the lion’s share of the work- plan on a week to receive the daphnia in the mail hour to set up a culture, and an hour to make solutions. After this, data collection is fairly quick- you could gather a reasonable amount of data in three 30-minute sessions (or one 90-minute microscope marathon) and be done. 


What is the project about?

Daphnia, otherwise known as water fleas, have a circulatory system similar to mammals. Most importantly, they have a chambered heart, which can be seen beating under a microscope. With a stopwatch and attention to detail, you can test whether a particular chemical has any effect on heart rate. 

What are the goals?

To determine if a particular chemical has an effect (increase or decrease) on the heart rate of Daphnia. 

Materials and Equipment / Ingredients 

What materials are required? 
  • Daphnia (water fleas)
  • Jar or other glass container and distilled water to make a habitat.
  • Bread yeast ( daphnia food)
  • Compound light microscope
  • Deep well microscope slides
  • Graduated cylinder
  • Graduated pipette/disposable pipettes
  • Stopwatch
  • Distilled water ( 1-2 gallons) or tap water left with open air for 48 hours
  • Chemical of your choice ( coffee, caffeine, weed killer, sports drinks, etc.)
Where can the materials be found? 
  • Aquarium store or online (site listed below)
  • Any large household jar- distilled water at the grocery.
  • Grocery store
  • High school science lab ( ask your science teacher)
  • Grocery or tap.
  • Grocery 


Background information 

Daphnia, otherwise known as water fleas, have a circulatory system similar to mammals. Most importantly, they have a chambered heart, which can be seen beating under a microscope. With a stopwatch and attention to detail, you can test whether a particular chemical has any effect on heart rate. 

Their hearts are found on their dorsal side ( their ‘backs’), above the brood pouch where you may find young if the Daphnia is a female. You can see a diagram of a typical Daphnia at this website: 

The heart can easily be seen beating- the only thing it might be confused with is/are young of the Daphnia, as they are moving as well, but not in as regular of a pattern. 

We can dilute certain chemicals and apply them to Daphnia, and watch to see if the heart rate changes! 

Any required diagrams/pictures (Pictures speak a thousand words!) 
See above link.  
Research Questions
  • What is a closed circulatory system?
  • How are Daphnia hearts like mammalian hearts?
  • How do chemicals affect heart rate? ( focus on your target chemical) 
Terms, Concepts and Questions to Start Background Research

Closed circulatory system, chambered heart, heart rate, caffeine (or other target chemical).

Experimental Procedure

Culture Prep:

  • After you receive your Daphnia, either in the mail or from the store, put them in a clean glass jar and add distilled room temperature water until full.
  •  Add JUST A TINY PINCH of yeast- too much will foul the water and kill the Daphnia. It is better to underfeed than overfeed.
  • Place in sunlight or under a lamp. Store this way until use. 
Solution Prep:
  • Use a graduated cylinder to mix 99ml of distilled water with 1 ml of your target chemical. If you are using a solid chemical, then 1g= 1ml.
  • Label this your 1% solution
  • Take 10 ml of your 1% solution and mix it with 90ml of distilled water. This will be your 0.1% solution
  • Solutions can be stored in rinsed plastic containers until needed. 
To take data:
  • Have ready your solutions, your culture, a stopwatch, slides, and a disposable pipette ( cut the tip off to allow a greater entrance to catch daphnia.
  • Catch a daphnia with the pipette ( you may want to practice this ahead of time!) and place into a the well on a deep well slide.
  • Use the microscope to get the daphnia in focus. If the Daphnia isn’t too large, you may want to use a cover slip to hold it in place.
  • Add two or three drops of your 1% solution. Using your stopwatch, count how many times the Daphnia’s heart beats in one minute. Return the Daphnia to the jar.
  • Do this at least 10 more times, and record heart rates. Find the average heart rate with a 1% solution.
  • Repeat all the above steps for your 0.1% solution, and again with your control ( plain water.) Don’t forget the control group, or you will have nothing to compare your solutions to!
  • Look at your data and come to a conclusion! 

You should take show all the data you took during the experiment in a table form. You should also include a graph of heart rate averages- a bar graph should do nicely. Any other statistical analysis- percent change, X-squared or t-tests (high school only)- can be added as well, if you know how to do them. 

While no diagrams are required, it is always a good idea to photo document the process so you have great visuals for your science fair board! 

This may be case where it is difficult to actually photograph Daphnia- ask you science teacher if she has a microscope camera. If not, it might be wise to use diagrams found on line to help your audience visualize Daphnia anatomy. 


Live Daphnia can be purchased here:

Daphnia Anatomy:
Microscope use:

Disclaimer and Safety Precautions provides the Science Fair Project Ideas for informational purposes only. does not make any guarantee or representation regarding the Science Fair Project Ideas and is not responsible or liable for any loss or damage, directly or indirectly, caused by your use of such information. By accessing the Science Fair Project Ideas, you waive and renounce any claims against that arise thereof. In addition, your access to's website and Science Fair Project Ideas is covered by's Privacy Policy and site Terms of Use, which include limitations on's liability.

Warning is hereby given that not all Project Ideas are appropriate for all individuals or in all circumstances. Implementation of any Science Project Idea should be undertaken only in appropriate settings and with appropriate parental or other supervision. Reading and following the safety precautions of all materials used in a project is the sole responsibility of each individual. For further information, consult your state's handbook of Science Safety.

Add to collection

Create new collection

Create new collection

New Collection


New Collection>

0 items