Daphnia & Caffeine

Daphnia is a microcrustacean that’s been the subject of biological investigations for more than a century. In fact, this tiny crustacean, also known as the water flea, was the first aquatic invertebrate to have its genome sequenced. Scientific research continues on this crustacean – from major universities and laboratories studying evolution to classrooms experiments that detail the effect of caffeine on daphnia.

Significance

Experiments on daphnia can be used to create theories on the effects that substances such as caffeine will have on humans, such as speeding up your heart rate. Daphnia is used as a surrogate species that helps scientists understand genomic responses to environmental stressors that often are important factors in the health of humans, according to the National Institutes of Health. The daphnia’s heartbeat can be measured under a microscope because its outer carapace is transparent, allowing you to see the internal organs.

Procedure

To perform an experiment in the classroom you divide daphnia into two containers. Add a diluted solution of caffeine or a caffeine-containing substance like an energy drink or coffee to one container and water to the other. The caffeine is your variable, so you must keep other factors the same between the two containers. For example, ensure the water temperature and dissolved oxygen are the same. If desired, you can have more than two containers and vary the amount of caffeine added.

Results

To check the results, remove a daphnia from the container with caffeine, place it under your microscope and count its heartbeats. Then remove one from the control container that contains no caffeine and count heartbeats. Repeat this procedure, recording your results, and then calculate an average for each container. “Cliffs AP Biology,” by Phillip E. Pack, recommends observing 20 daphnia from each container. The body diameter of an adult daphnia averages 3 mm to 5 mm.

Consideratons

Since caffeine is a stimulant, your expected result is a faster heartbeat among the daphnia placed in the caffeine solution, Pack notes. Use caution because adding too much caffeine to your container may kill the daphnia. ScienceBuddies.org recommends conducting a pilot experiment first to determine the best dose or doses of caffeine to use on the crustacean. Caffeine is a central nervous system stimulant. An overdose in humans can cause rapid or irregular heartbeat, dizziness, breathing problems, hallucinations, muscle twitches, confusion and convulsions. In humans, lethal toxicity is estimated at 150 to 200 mg per 2.2 lb. body weight, or 80 to 100 cups of coffee in an extremely short time frame.