Question

Photorespiration occurs in
A.Green photosynthetic parts
B.All living cells
C.Mitochondria
D.Root

Answer 1

Hint: Photorespiration is a process in plant metabolism where the enzyme RuBisCO oxygenates RuBP, wasting some energy produced in photosynthesis.

Complete step by step answer:
1.Photorespiration can be defined as a process that occurs in green cells in presence of light releasing an extra amount of CO2. Green cells have chloroplast in them where photosynthesis occurs.
2.Warburg (1920) had observed that excess O2 in the atmosphere inhibits the rate of photosynthesis in green algae. Later on, it was observed in many green plants. However, this inhibition was evident in C3 plants and not in C4 plants. This inhibition was understandable after the discovery of photorespiration.
3.The cellular site of photorespiration is peroxisomes. However, three cell organelles like chloroplast, peroxisome and mitochondria take part in the process. The substrate of photorespiration is glycolic acid synthesized in chloroplast when the rate of photosynthesis : respiration is 10:1 during the noon. It results in excess production of oxygen.
RuBP+O2→2phosphoglycolic acid+3PGA
2phophoglycolic acid+H2O→glycolic acid+phosphoric acid
4.Glycolic acid is transported from chloroplast to peroxisome. Further reactions take place and finally CO is given out from mitochondria.
5.In the photorespiratory pathway, there is no ATP generation but ATP is consumed. Therefore, photorespiration is a wasteful process.
6.Usually O2 concentration has no effect on dark respiration but photorespiration depends upon Oxygen concentration and is directly proportional to it. It indicates that respiration in the dark is quite different from respiration in light.

Hence the correct answer is option(A)

Note: In C4, plants photorespiration does not occur. This is because they present a mechanism that increases the concentration of CO, at the enzyme site. This takes place when the C, acid from the mesophyll is broken down in the bundle sheath cells to release CO, - this results in increasing the intracellular concentration of CO,. In exchange, this ensures that the RuBisCO functions as a carboxylase minimising the oxygenase activity.