Daphnia Lab Report Essay

Daphnia are cold-blooded poikilotherms that rely on heat from the surrounding water to maintain their body temperature. An increase in the water temperature should equate to an increase in metabolic activity due to enzymes working at a temperature closer to their optimum level. However, once the optimum temperature has been exceeded, the enzymes will begin to denature. Hydrogen bonds, which keep the protein conformation, begin to break, causing a change in shape of the active site; substrates can no longer be catalysed, resulting in a dramatic slowing of cellular metabolism. Faster heart contractions pump more nutrient-carrying hemolymph to the Daphnia's organs, tissues and cells, meeting the increasing demand for energy, in the form of ATP, needed for cellular respiration, movement and the building of body mass. When the surrounding water temperature decreases, a falling heart rate should be seen as enzyme activity slows down. The translucent exoskeleton of the Daphnia will allow heart contractions to be seen and counted when viewed through a light microscope. Using this information will allow the correlation between temperature and heart rate to be examined. (Background information on Daphnia) (Deken)

Hypothesis
Observing Daphnia changing from sexual to asexual reproduction when environmental conditions become critical would be difficult to quantify in a school laboratory; therefore I decided to investigate the effect of temperature on the heart rate of Daphnia, with a view to identifying when critical temperatures were reached. The research question was: What effect does temperature change have on the heart rate of Daphnia? Leading on from this, I hypothesised: From a starting temperature of 0°C, raising the temperature of the water surrounding the Daphnia would increase their heart