Photorespiration Questions in English

(A) Photorespiration is a light-dependent process in which $O_2$ binds to $RuBisCO$ instead of $CO_2$,leading to the oxidation of organic compounds.
It is considered a wasteful process because it consumes energy ($ATP$ and $NADPH$) and releases $CO_2$ without producing sugars or $ATP$,thereby reducing the overall efficiency of photosynthesis.

(C) Photorespiration is a complex metabolic pathway that involves three different cell organelles. It is initiated in the chloroplast,continues in the peroxisome,and is completed in the mitochondria. The loss of $CO_2$ during photorespiration occurs in the mitochondria,not the cytoplasm. Therefore,the match 'Photorespiratory loss of $CO_2$ - Cytoplasm' is incorrect.

(A) Photorespiration is a wasteful process that occurs in $C_3$ plants. It involves three organelles: the chloroplast,peroxisome,and mitochondria.
$1$. In the chloroplast,$RuBP$ reacts with $O_2$ to form $2$-phosphoglycolate.
$2$. In the peroxisome,glycolate is converted into glycine.
$3$. In the mitochondria,two molecules of glycine are converted into one molecule of serine,and during this process,$CO_2$ and $NH_3$ are released.

(D) Photorespiration is a light-dependent process that occurs in $C_3$ plants.
It involves the coordinated activity of three cell organelles: chloroplasts,peroxisomes,and mitochondria.
Since it requires light,it occurs during the day.
Therefore,all the given statements are correct.

(D) Photorespiration is a complex metabolic pathway involving three organelles: the chloroplast,peroxisome,and mitochondria.
In the chloroplast,the enzyme $RuBisCO$ acts as an oxygenase,leading to the oxidation of $RuBP$.
Additionally,the light-dependent reactions occurring in the chloroplast involve the phosphorylation of $ADP$ to $ATP$.
Therefore,both phosphorylation and oxidation processes occur within the chloroplast during photorespiration.

(A) In the process of photorespiration,the enzyme $RuBisCO$ acts as an oxygenase.
When $RuBP$ (a $5$-carbon compound) reacts with $O_2$,it undergoes oxygenation instead of carboxylation.
This reaction produces one molecule of $3$-carbon compound,$3$-phosphoglycerate $(PGA)$,and one molecule of $2$-carbon compound,phosphoglycolate.
Therefore,the correct product is $3$-phosphoglycerate + phosphoglycolate.

(D) Photorespiration is a complex metabolic pathway that involves the cooperation of three different cell organelles: the $Chloroplast$, the $Peroxisome$, and the $Mitochondria$.
$1$. In the $Chloroplast$, the enzyme $RuBisCO$ acts as an oxygenase, reacting $RuBP$ with $O_2$ to form $2$-phosphoglycolate.
$2$. The $2$-phosphoglycolate is then transported to the $Peroxisome$, where it is converted into glycine.
$3$. Glycine is then transported to the $Mitochondria$, where it is converted into serine, releasing $CO_2$ and $NH_3$.
$4$. Finally, the serine returns to the $Peroxisome$ and then to the $Chloroplast$ to regenerate $RuBP$.
Since all three organelles are essential for the completion of this pathway, the correct answer is $All\,of\,the\,above$.

(A) Photorespiration is a process in which the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
This process involves the loss of fixed carbon as $CO_2$ and does not produce $ATP$ or $NADPH$.
Because the first stable product formed in this pathway is a $2$-carbon compound called phosphoglycolate,photorespiration is also known as the $C_2$ pathway.

(A) In $C_3$ plants,the enzyme $RuBisCO$ (Ribulose$-1,5-$bisphosphate carboxylase-oxygenase) has an affinity for both $CO_2$ and $O_2$.
During photorespiration,the concentration of $O_2$ is higher or the ratio of $O_2$ to $CO_2$ favors the oxygenation reaction.
In this process,$RuBisCO$ acts as an oxygenase,binding $O_2$ with $RuBP$ (Ribulose$-1,5-$bisphosphate) instead of $CO_2$,leading to the formation of one molecule of phosphoglycerate and one molecule of phosphoglycolate.
Therefore,in photorespiration,$RuBisCO$ functions as an oxygenase.

(A) Photorespiration is a wasteful process that occurs in $C_3$ plants.
$1$. In the photorespiratory pathway,there is no synthesis of $ATP$ or $NADPH$. In fact,it consumes energy.
$2$. It results in the loss of fixed carbon as $CO_2$,thereby reducing the overall productivity of the plant.
$3$. It is believed to play a protective role by preventing the photo-oxidation of chlorophyll under high light intensity and low $CO_2$ concentrations.
$4$. Plants with Kranz anatomy (like $C_4$ plants) have a mechanism to increase $CO_2$ concentration around the enzyme $RuBisCO$,which minimizes photorespiration.
Therefore,the statement that $ATP$ and $NADPH$ are synthesized is incorrect.

(C) Photorespiration is a complex metabolic pathway involving three organelles: the chloroplast,the peroxisome,and the mitochondria.
$1$. In the chloroplast,$RuBP$ reacts with $O_2$ to form $3-PGA$ and $2-phosphoglycolate$.
$2$. The $2-phosphoglycolate$ is converted into glycolate,which moves to the peroxisome.
$3$. In the peroxisome,glycolate is converted into glycine.
$4$. Two molecules of glycine enter the mitochondria,where they are converted into one molecule of serine,releasing $CO_2$ and $NH_3$ in the process.
Therefore,$CO_2$ is released specifically in the mitochondria.

(B) Photorespiration is a complex metabolic process that involves three distinct organelles: the chloroplast,the peroxisome,and the mitochondria.
$1$. In the chloroplast,the enzyme RuBisCO acts as an oxygenase,leading to the formation of phosphoglycolate.
$2$. In the peroxisome,glycolate is oxidized to glyoxylate by the enzyme glycolate oxidase,which consumes $O_2$.
$3$. In the mitochondria,glycine is converted to serine,a process that releases $CO_2$ and $NH_3$.
Since the oxidation reaction involving $O_2$ specifically occurs in the chloroplast (RuBisCO oxygenase activity) and the peroxisome (glycolate oxidase activity),the process involves oxidation in $2$ organelles.

(C) Photorespiration is a complex metabolic pathway involving three organelles: the chloroplast,the peroxisome,and the mitochondria.
$1$. In the chloroplast,$RuBP$ reacts with $O_2$ to form $2$-phosphoglycolate.
$2$. This $2$-phosphoglycolate is dephosphorylated to form glycolate,which moves to the peroxisome.
$3$. In the peroxisome,glycolate is converted into glycine,which is the simplest amino acid.
$4$. Therefore,the peroxisome is the organelle responsible for the synthesis of glycine (the simplest amino acid) during the photorespiratory pathway.

(B) Statement $I$ is true: In $C_3$ plants,the enzyme $RuBisCO$ has an affinity for both $CO_2$ and $O_2$. When $O_2$ concentration is high,$RuBisCO$ binds with $O_2$ instead of $CO_2$,leading to photorespiration,which reduces the efficiency of $CO_2$ fixation.
Statement $II$ is false: $C_4$ plants have evolved a mechanism to avoid photorespiration. They lack $RuBisCO$ in mesophyll cells,and bundle sheath cells maintain a high concentration of $CO_2$ around $RuBisCO$,effectively eliminating photorespiration in both cell types.

(B) The correct answer is $B$. Both statements $A$ and $B$ are correct.
Photorespiration is a wasteful process in $C_3$ plants.
In $C_3$ plants,some $O_2$ binds to $RuBisCO$ instead of $CO_2$,which decreases the efficiency of $CO_2$ fixation.
In this pathway,$RuBP$ binds with $O_2$ to form one molecule of phosphoglycerate $(3C)$ and one molecule of phosphoglycolate $(2C)$.
During the photorespiratory pathway,there is no synthesis of sugars,$ATP$,or $NADPH$. Instead,it leads to the release of $CO_2$ and the consumption of $ATP$.