Answer:
Oxygen
Explanation:
Oxygen is the by product of photolysis during photosynthesis whereby water molecules are split to form protons (H+ ions), electrons and oxygen (by product).
Oxygen is not needed during any of the reactions in photosynthesis and Calvin cycle and will not affect the rate of photosynthesis or possibility of photosynthesis occurring. However, it will affect the process of aerobic respiration instead.
Carbon dioxide is needed in carbon fixation during the Calvin cycle. Without it, 6 carbon sugars cannot be formed.
Water is needed for photolysis to produce protons (maintain the electrochemical gradient) and electrons (to replenish lost electrons)
Chlorophyll are pigments that harvest light energy to excite electrons produced from photolysis of water to be passed down the electron transport chain.
Light is needed as a source of energy to energise the electrons
