The upcoming discussion will update you about the difference between Photorespiration and True Respiration.
1. Effect of O2 Concentration:
The most obvious difference between true respiration and photorespiration is the effect of oxygen concentration on the rate of two processes. In most tissues true respiration is saturated at oxygen concentration of 2-3% and and beyond this percentage virtually no increase occurs. On the other hand, photorespiration increases steadily with the increased oxygen concentration from 0-100%.
2. Requirement of Photosynthetic Apparatus:
Whereas true respiration can occur in any cell, photorespiration is essentially linked with photosynthesis and occurs only in photosynthetic cells. In fact an active photosynthetic system was necessary for photorespiration to occur. Through the use of DCMU (Dichlorophenyl dimethyl urea), a photosynthetic inhibitor, on leaves, it is observed that CO2 evolution is insensitive to change in O2 concentration and was attributed to dark respiration.
3. Nature of the Substrate:
Studies of Goldsworthy (1966) have shown that the two processes use different substrates. Using 14CO2 they demonstrated that the CO2 released by the leaf in the presence of light was about twice as given off in the dark, suggesting the involvement of two different substrates for photosynthesis and photorespiration.
4. Energy Relationship:
Evidently, the biochemistry of the two processes also differs fundamentally. For instance, in true respiration, the oxidation of substrates yields CO2 and energy mainly in the form of ATP and reduced pyridine nucleotides. On the other the hand, photorespiration does not produce ATP or reduced nucleotides.
Instead it causes oxidation of glycolate which arises as an unwanted by-product of photosynthesis. The carbon or glycolate after oxidation is converted to carbohydrate but the remainder is converted to CO2 which is released as the CO2 of photorespiration. Indeed photorespiration actually uses energy in the form of ATP and reduced nucleotides.