What is photosynthesis?
The synthesis of complex organic compounds from simple organic compounds like water and carbondioxide by green plants in the presence of chlorophyll using sunlight is called photosynthesis.
6CO2+ 6H2O CHO+6O
Explain the mechanism of photorespiration.
The utilization of oxygen and release of carbondioxide in presence of light during high temperature and low concentration of CO2 is called photorespiration.
It proceed in the following mechanism:-
1. During high temperature, high concentration of O2 and low concentration of CO2, the affinity of Ribulose bi-phosphate (RuBP) carboxylase for CO₂ decreases and for O₂ increases and form oxyɡenase which catalyse the oxidation of RuBP to form 3-PGA(3-phospgoglyceric acid) and 2-phosphoglycolate.
RuBP +O₂ →3-PGA + 2-phosphoglycolate
2. Phosphoglycolate loses phosphate group and form glycolate.
Phosphoglycolate + H2O → glycolate + H₃PO₄
3. Glycolate is passed into perioxysomes of mesophyll and oxidized to glyoxylate.
Glycolate +O₂ →Glyoxylate + H₂O₂ (oxidase)
H₂O₂→ 2H₂O +O₂ (catalase)
Glyoxylate → Glycine (transaminase)
4. Glycine from serine which passed to mitochondria which is converted to 3-phospgoglyceric acid and 3-PGA is transported to chloroplast for synthesis of RuBP. This process is repeated. Photorespiration produces two carbon compound. So it is also called C2 cycle.
2-Glycine → serine +CO2
Serine + ATP → PGA +NH₃ + ADP