Question : Describe photorespiration.

1.	Question : Describe photorespiration.
Answer» Solution :The respiration which occurs in presence of light and in chlroplast is called photorespiration. To understand photorespiration we have to know a little bit more about the first step of the Calvin - pathway. In this reation RUBP combines with `CO_(2)` to form 2 molecules of 3PGA, that is catalysed by RuBisCO. `RuBP + CO_(2)overset("RuBisCO)rarr2xx3PGA` RuBisCO : That is the most abundant enzyme in the world. Characteristic : It is CHARACTERISED by the fact that its active site can BIND to both `CO_(2) and O_(2)` - hence the name. Specially : RuBisCO has a much greater affinty for `CO_(2)` than for `O_(2)`. Base : It is the relative concentration of `O_(2) and CO_(2)` that determines which of the twowill bind to the enzyme. In `C_(3)` plants some `O_(2)` does bind to RuBisCO and hence `CO_(2)` fixation is decreased. Here the RuBP instead of being converted to 2 molecules of PGA binds with `O_(2)` to from molecule of phosphoglycerate and phosphoglycolate in a pathway called photorespiration. In the photorespiratory pathway, there is neither SYNTHESIS of sugars, nor of ATP Rather it results in the release of `CO_(2)` with the utilisation of ATP. In the photorespiratory pathway there is no synthesis of ATP or NADPH. THEREFORE, photorespiration is a wasteful process.

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