Measuring Heart Rate in Daphnia

Watch Their Hearts Beat: A Daphnia Lab That Brings Biology to Life

An Unexpected Star in the Biology Lab:  Need a classroom lab that’s easy to set up, exciting to run, and packed with teachable moments? Meet Daphnia—a tiny aquatic crustacean with a see-through body and a heart you can actually see beating under a microscope. It’s weird. It’s wonderful. And it’s the perfect hook for teaching circulatory systems, environmental effects on physiology, and graphing real data.

This Daphnia heart rate lab checks all the boxes for a super-engaging, low-prep biology investigation. Students get hands-on experience with live organisms, observe real-time physiological changes, and collect data that sparks discussion and curiosity. This lab encourages deeper thinking, reinforces graphing skills, teaches the scientific method and experimental design, and turns abstract textbook concepts into visual, measurable experiences.

What Students Discover: When Daphnia are placed in environments of varying temperatures, their heart rates respond—dramatically. Students watch as these tiny creatures go from chilled-out to heart-racing, helping them understand the link between metabolism and temperature in ectothermic animals. 

Even better? Students can extend the lab activity by designing their own experiment to test a different variable —testing how caffeine, pollutants, or pH levels influence heart rate. Honors and AP students can take it further by calculating Q₁₀ temperature coefficients, analyzing their results like real researchers.

Please note: Teach students to respect all living organisms. No harm should come to the Daphnia in this experiment.

This isn’t just a fluff activity. The Daphnia heart rate lab builds core science skills:

• Graphing and analyzing data
• Comparing variables and controls
• Designing and running investigations
• Problem solving and critical thinking

It also supports NGSS and AP Biology objectives, from cellular processes to environmental impacts on organisms.

The biggest problem with this lab is helping students find the heart. The digestive system of Daphnia is quite active, and the students often think that the moving digestive system is the heart. The heart is located just behind the head on the dorsal surface of the body.  It will appear as a very small, clear and transparent, beating sack.

Classroom-Ready, Teacher-Approved: Looking for something that won’t eat up your prep time? This Daphnia heart rate resource comes with the following.

• Clear student worksheets
• Ready-to-go graphing templates
• Background reading for context
• Optional extensions for advanced learners
• A teacher guide to make implementation a breeze

Ready to Try It?

This lab isn't just about watching hearts beat—it’s about getting your students excited to learn. Whether you're teaching standard biology, honors, or AP, this investigation delivers science that sticks.

👉  Click here: Measuring the Heart Rate in Daphnia

The benefits of this lab? 

• Labs keep the student excited and interested in science.  
• If the student views your class as "fun", they are more likely to perform well in the parts of the class that are less fun.....think lecture days.
• Working with living organisms is a fundamental part of a biology class and should be included at every opportunity.
• Students gain an appreciation for the living world when they get to view organisms that they are unlikely to see or notice in nature.

What do you do with the Daphnia when the lab is over?  Well, our Daphnia will spend the remainder of their days in my Elodea tank!