Decay of biological material
Method overview
Place equal samples at different controlled temperatures, add the same decomposer/enzyme source, start timing and measure pH or indicator change to a fixed endpoint. Repeat and calculate rate.
Apparatus set-up
Diagrammilk or organic material; lipase/microorganisms; pH indicator/probe; water baths; timer; thermometers
Independent variable
temperature
Dependent variable
time for colour/pH change or rate of decay
Control variables
sample volume; starting pH; organism/enzyme concentration; oxygen; measurement endpoint
Apparatus
milk or organic material; lipase/microorganisms; pH indicator/probe; water baths; timer; thermometers
Safety
Use school-safe organisms/materials; wear eye protection; avoid opening incubated cultures; wash hands.
Scientific rationale
Temperature affects enzyme-controlled reactions in decomposers; a fixed endpoint permits fair timing; pH change can indicate product formation.