Photosynthesis is the major process by which light from the sun is captured by plants, algae and some bacteria to produce energy. It is a process in which light energy is converted into chemical energy which is then stored in sugars. Photosynthesis occurs in two stages, light-dependant reactions and light-independent reactions. In light-dependent reactions the chlorophyll traps light energy which is then used to excite electrons and split water molecules into hydrogen and oxygen. ATP and NADPH are produced in this reaction. In light-independent reactions the ATP and NADPH produced from the previous reactions are used to power a series of reactions in which atmospheric carbon dioxide is used to synthesis carbohydrates(P.121, The Living World, 7th Ed). Photosystem II is the first protein complex in the light-dependent reactions. The portion of the protein that contains the pigment molecules is called the antenna complex. The antenna complex captures energy from photons and transfers into the reaction center chlorophyll, which is the P680. Once excited the P680 gives up an electron to the electron transport chain. The empty electron orbital formed is filled with an electron from a water molecule (P.126, The Living World, 7th Ed). This is achieved by the presence of a water splitting enzyme, which splits the water molecule into hydrogen and oxygen with the release of an electron. As a result, we can calculate the rate of photosynthesis my measuring the rate of oxygen production.
Graph 1. Evolution of oxygen with time (including the slope at each phase of the experiment).
Table 1. Oxygen evolution and the photosynthetic rate at each phase. Condition| Slope(% O2/min)| Photosynthetic Rate(µmol O2/m²/min)| Phase 1| 0.035| 156.967|
Phase 2| 0.058| 260.116|
Phase 3| 0.040| 179.391|
Dark| 0.022| 98.665|
(Including answers to questions asked)
From the graph obtained...