If a mutation occurs such that the photosystem no longer functions as efficiently as it should, The amount of oxygen produced will be most directly affected.
The photosystem uses energy from sunlight to split a water molecule; this is done by taking an electron. After splitting the water molecule (by taking an electron), electrons are moved to the plastoquinone from the protein complex after splitting of the water molecule. This results in evolving of oxygen molecules. The hydrogen left is used to reduce carbon dioxide to glucose.
