Determination of photosynthesis rate by polarographic oxygen measurement method.
The method is used in photosynthesis intensity measurement by rate of oxygen release by biological objects (microalgae, cyanobacteria).
The rate of photosynthesis is determined by polarographic method. Clark electrode has a platinum electrode separated from the test solution by a membrane used as a cathode and silver chloride electrode immersed into concentrated KCl solution used as an anode. Polarographic method for determining oxygen concentration in the medium is based on oxygen reduction reaction on the cathode. Under these conditions, the electrochemical (cathodic) oxygen reduction current is driven by addition of four electrons to oxygen in the reaction О2 + 4е− + 4Н+ → 2Н2О. The initial reaction on the platinum electrode (cathode) is followed by formation of OH− ions:
О2 + 4е− + 2Н2О → 4ОН−
Then OH− ions diffuse to the reference electrode (anode) and form Ag2O in reaction with silver:
4OH− + 4Ag → 2Ag2O + 2Н2О + 4е−
Thus, the oxygen reduction reaction on the platinum electrode gives hydroxide ion, which then reacts with the reference electrode (anode). Based on polarographic waves obtained by the reduction of oxygen, its concentration is determined by potential, which is proportional to oxygen concentration in the medium.
As part of the school, photosynthetic oxygen evolution by cyanobacteria is proposed to be measured by Clark electrode.
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