Heart Rate of Daphnia

Heart rate of Daphnia


Investigating the effect of caffeine on the heart rate of Daphnia.


Daphnia are small water fleas (a type of crustacean) which are less than 3mm (on average). They are an invertebrate which has a hard shell outer body which is translucent. The hard outer shell protects the body excluding the head. There normal environment are lakes and ponds which are between 21-24°C which help them to reproduce quick. The daphnias eat all kinds of algae and vegetation.

Caffeine is a stimulant that increases your heart rate and can affect other parts of the body such as the nervous system; the caffeine increases the amount of stimulatory transmitters to be released. Caffeine dissolves in liquids and is a cause of many health problems such as heart, digestive and circulation problems.


I predict the more caffeine which the daphnia is exposed to increases the heart rate; the more caffeine that the daphnia absorbs in the blood stream the faster the heart rate.
Equipment (initial)

Light microscope
Glass slide
Beaker (100ml)
Stop clock

Lab book


-Ensure the wire of the microscope does not dangle off of the bench; this could get pulled off the table due to people walking past and people could trip over the wire.

-The placing of the equipment; the beaker of water and daphnias need to be kept on the bench away from the edge to make sure it does not get knocked off. If knocked off the daphnias will die and the water is a hazard for others.

-Ensure the water and electricity (microscope wire, plug socket) are kept apart. The beaker of water and daphnia could spill onto the wire and electrocute someone or blow the electrics.

-Make sure you handle the daphnias in the carefully and correctly. To get them out of the beaker of water use a pipette and gently squeeze onto the glass slide. To get the daphnia off the glass slide and back into the beaker; tilt the...