Looking for classes? Ksquare Career Institute, Bengaluru →
During photorespiration the oxygen consuming reaction(s) occur in -
A
Stroma of chloroplasts and mitochondria
B
Stroma of chloroplasts and peroxisomes
C
Grana of chloroplasts and peroxisomes
D
Stroma of chloroplasts
Detailed Solution
Photorespiration involves three organelles: the chloroplast, the peroxisome and the mitochondrion.
First oxygen-consuming reaction: in the stroma of the chloroplast, RuBisCO acts as an oxygenase and combines RuBP with $O_2$ to form one molecule of phosphoglycerate (3 C) and one molecule of phosphoglycolate (2 C).
The phosphoglycolate is converted into glycolate, which moves into the peroxisome.
Second oxygen-consuming reaction: in the peroxisome, glycolate is oxidised to glyoxylate by the enzyme glycolate oxidase, which uses $O_2$ and forms $H_2O_2$.
The glyoxylate is converted to glycine, which enters the mitochondrion; there two molecules of glycine give serine with the release of $CO_2$ and $NH_3$. Oxygen is not consumed in this step.
The grana are the site of the light reaction, where oxygen is evolved, not consumed.
So the oxygen consuming reactions occur in the stroma of chloroplasts and in peroxisomes.
First oxygen-consuming reaction: in the stroma of the chloroplast, RuBisCO acts as an oxygenase and combines RuBP with $O_2$ to form one molecule of phosphoglycerate (3 C) and one molecule of phosphoglycolate (2 C).
The phosphoglycolate is converted into glycolate, which moves into the peroxisome.
Second oxygen-consuming reaction: in the peroxisome, glycolate is oxidised to glyoxylate by the enzyme glycolate oxidase, which uses $O_2$ and forms $H_2O_2$.
The glyoxylate is converted to glycine, which enters the mitochondrion; there two molecules of glycine give serine with the release of $CO_2$ and $NH_3$. Oxygen is not consumed in this step.
The grana are the site of the light reaction, where oxygen is evolved, not consumed.
So the oxygen consuming reactions occur in the stroma of chloroplasts and in peroxisomes.