Rate of photosynthesis
Method overview
Place pondweed in sodium hydrogencarbonate solution, allow it to acclimatise, set a measured lamp distance, record oxygen production for a fixed time, repeat and calculate a mean. Test several distances and control temperature.
Apparatus set-up
Diagrampondweed; lamp/LED; ruler; sodium hydrogencarbonate solution; thermometer; stopwatch; gas syringe/capillary
Independent variable
light intensity or distance from lamp
Dependent variable
oxygen bubbles per minute or oxygen volume per time
Control variables
temperature; carbon dioxide concentration; pondweed length/species; wavelength; measurement time
Apparatus
pondweed; lamp/LED; ruler; sodium hydrogencarbonate solution; thermometer; stopwatch; gas syringe/capillary
Safety
Keep water away from electrical equipment; lamp may become hot; use an LED or heat shield.
Scientific rationale
Sodium hydrogencarbonate supplies carbon dioxide; acclimatisation allows the rate to stabilise; temperature must be controlled because photosynthesis is enzyme-controlled.