What is photorespiration.....
Answers
★ PHOTORESPIRATION:-
ln Calvin pathway, RuBP combines with CO2.
→ RuBisCO is the most abundant enzyme in the world. Its active site can bind to both CO2 and 02.
→ RuBisCO has a much greater affinity for CO2 than for O2. This binding is competitive. Relative concentration of O2 and CO2 determines which one will bind to the enzyme.
→ In C3 plants some 02 bind to RuBisCO. Hence CO2 fixation is decreased. Here RuBP binds with O, to form one molecule of phosphoglycerate and phosphoglycolate. This pathway is called photorespiration.
→ In this pathway, there is no synthesis of sugars, ATP and NADPH. Hence photorespiration is a wasteful process. Rather it causes the release of CO2 by using ATP.
→ In C4 plants photorespiration does not occur because they can increase CO2 concentration at the enzyme site.
→ This takes place when C4 acid from the mesophyll is broken down in the bundle cells to release CO2. This minimises the oxygenase activity of RuBisCO.
→ Due to the lack photorespiration, productivity and yields are better in C4 plants. In addition these plants show tolerance to higher temperatures.