In this experiment, we determined the rate of photosynthesis by measuring the rate of oxygen production. It can be carried out as a result of PSII activity. Photosystem II is the first antenna complex in the light-dependent reactions. It is located in the thylakoid membrane. The enzyme captures photons of light to stimulate electrons to an excited state. Then, the high-energy electron will transferred through a variety of coenzymes and cofactors to reduce plastoquinone to plastoquinol. The electrons loss in PSII is replaced by oxidizing water to form hydrogen ions and molecular oxygen. The splitting of water provides H+, electron and release oxygen as by-product. Therefore we can determine the rate of photosynthesis by the change in oxygen concentration in the experiment.
Condition Slope (% O2/min) Photosynthetic Rate (μmol O2/m2/min)
Initial phase 0.028 470.60
Middle phase 0.043 722.72
Final phase 0.024 403.38
Dark phase 0.016 268.92
Table 1:slope and photosynthetic rate in different phase
Setting of the experiment:
At the beginning, the oxygen concentration dropped to around 7.85%. it is because one of our group mate do some gentle exercise and we collect the exhaled gas to flush the gas chamber with a higher concentration of CO2. Thus, we can obtain a sharper change during the experiment.
The water placed between the light and the chamber act as a cooling agent to prevent absorption of heat of the sample leaf. The water can absorb most of the heat from the light due to the high heat capacity. Therefore, we can avoid the effect of temperature on the photosynthesis.
The halogen light is used in the experiment so as to provide more photon within a short period. Since that halogen light is more reactive and thus has a higher luminous efficiency. This, it can provide more photon to accelerate the photosynthesis through out the whole experiment so that a sharper result can be obtained...