Photorespiration Questions in English

(D) Photo-respiration is a complex metabolic pathway that involves the cooperation of three distinct cell organelles:
$1$. $Chloroplast$: The process begins here with the oxygenation of $RuBP$ by the enzyme $RuBisCO$.
$2$. $Peroxisome$: The intermediate products (like glycolate) are transported here for further processing.
$3$. $Mitochondria$: The final steps of the pathway occur here, where glycine is converted into serine, releasing $CO_2$ and $NH_3$.
Therefore, all three organelles are involved in the process of photo-respiration.

(B) In plant cells,peroxisomes play a crucial role in the process of photorespiration.
Photorespiration is a metabolic pathway that occurs in photosynthetic organisms,involving the cooperation of three organelles: chloroplasts,peroxisomes,and mitochondria.
During this process,the enzyme $RuBisCO$ acts on oxygen instead of carbon dioxide,leading to the production of phosphoglycolate,which is then processed in the peroxisomes to recover carbon.

(D) Photorespiration is quite different from respiration as no $ATP$ or $NADH$ are produced, and the energy released is lost as heat.
Moreover, the process is considered wasteful for plants because up to $50\%$ of the photosynthetically fixed $CO_2$ (in the form of $RuBP$) can be lost to the atmosphere through this process.

(D) Photorespiration is a process that occurs in $C_3$ plants,not $C_4$ plants. In $C_4$ plants,photorespiration does not occur because they have a specialized leaf anatomy known as $Kranz$ anatomy,which increases the concentration of $CO_2$ around the enzyme $RuBisCO$,thereby minimizing the oxygenase activity of the enzyme. Therefore,the statement that it is a characteristic of $C_4$ plants is incorrect.

(B) In $C_3$ plants, when $O_2$ concentration is high, the enzyme $RuBisCO$ acts as an oxygenase.
This leads to the oxygenation of $RuBP$ (Ribulose$-1,5-$bisphosphate).
The reaction is: $RuBP + O_2 \xrightarrow{RuBisCO} \text{Phosphoglycolate} (2C) + \text{Phosphoglycerate} (3C)$.
Phosphoglycolate is the primary product formed due to the oxygenase activity of $RuBisCO$ during photorespiration.

(A) Photorespiration is also known as the $C_2$ cycle.
This is because the first stable product formed during this process is a $2$-carbon compound called phosphoglycolate.
Unlike the $C_3$ cycle (Calvin cycle) where the first product is a $3$-carbon compound,photorespiration involves the oxygenase activity of the enzyme RuBisCO,leading to the formation of a $2$-carbon molecule.

(C) Photorespiration occurs under specific conditions:
$(1)$ High $O_2$ concentration.
$(2)$ Low $CO_2$ concentration.
$(3)$ High light intensity.
In the presence of high $O_2$ and low $CO_2$,the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase. Therefore,the first reaction in photorespiration is the oxygenation of $RuBP$ (Ribulose$-1,5-$bisphosphate),which leads to the formation of one molecule of phosphoglycerate and one molecule of phosphoglycolate.

(D) In the process of photorespiration,glycolate is first oxidized to glyoxylate in the peroxisome. Glyoxylate is then converted into glycine. Two molecules of glycine enter the mitochondria,where they are converted into one molecule of serine and one molecule of $CO_2$ along with the release of $NH_3$.

(B) $Photorespiration$ occurs in photosynthetic cells,specifically in the green parts of the plant in the presence of light energy.
It involves three organelles: chloroplasts,peroxisomes,and mitochondria.

(C) Peroxisomes are specialized organelles involved in photorespiration in plants. In $C_3$ plants,photorespiration involves the cooperation of three organelles: chloroplasts,peroxisomes,and mitochondria. These organelles are primarily located in the mesophyll cells where the photosynthetic machinery is active. Therefore,peroxisomes are found in mesophyll cells.

(B) The process of photorespiration involves the coordinated action of three cell organelles: the chloroplast,peroxisomes,and mitochondria. Peroxisomes specifically house enzymes like glycolate oxidase,which are essential for the conversion of glycolate to glyoxylate during this pathway.

(C) Photorespiration is a metabolic pathway that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase. This process involves three distinct cell organelles:
$1$. $Chloroplasts$: Where the initial reaction occurs, producing phosphoglycolate.
$2$. $Peroxisomes$: Where glycolate is processed into glycine.
$3$. $Mitochondria$: Where two molecules of glycine are converted into one molecule of serine, releasing $CO_2$ and $NH_3$.

(B) In $C_3$ plants,the enzyme $RuBisCO$ can bind to both $CO_2$ and $O_2$.
When the concentration of $O_2$ increases in the atmosphere,$RuBisCO$ acts as an oxygenase rather than a carboxylase.
This leads to a process called photorespiration,where $O_2$ is consumed and $CO_2$ is released without the production of $ATP$ or $NADPH$.
Consequently,the rate of photosynthesis decreases because the efficiency of carbon fixation is reduced.

(C) Wheat is a $C_3$ plant. In $C_3$ plants,the enzyme $RuBisCO$ acts as both a carboxylase and an oxygenase. When $O_2$ levels are high,$RuBisCO$ binds to $O_2$ instead of $CO_2$,leading to photorespiration,which reduces the efficiency of photosynthesis. Therefore,if the supply of $O_2$ is decreased,photorespiration is inhibited,allowing more $RuBisCO$ to bind with $CO_2$,which results in an increase in the rate of photosynthesis.

(C) Photorespiration is a process in $C_3$ plants where the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase when oxygen levels are high.
When the concentration of oxygen in the atmosphere decreases,the rate of photorespiration decreases.
Since photorespiration consumes energy and releases $CO_2$ without producing sugars,a reduction in this process allows $RuBisCO$ to function more efficiently as a carboxylase.
Consequently,the efficiency of the $C_3$ cycle increases.
$C_4$ plants have a mechanism to concentrate $CO_2$ around $RuBisCO$,which minimizes photorespiration regardless of external oxygen levels; therefore,the $C_4$ cycle remains largely unaffected by changes in atmospheric oxygen concentration.

(B) The $C_2$ cycle is another name for photorespiration.
Photorespiration is a metabolic pathway that occurs in plants when the enzyme RuBisCO acts on oxygen instead of carbon dioxide.
This process is characteristic of $C_3$ plants,not $C_4$ plants,as $C_4$ plants have evolved mechanisms to minimize photorespiration.
Therefore,the $C_2$ cycle is studied in plants that exhibit photorespiration.

(D) Photorespiration is a complex metabolic pathway that involves the cooperation of three distinct cell organelles:
$1$. $Chloroplast$: Where the initial reaction occurs involving $RuBisCO$ and $O_2$.
$2$. $Peroxisome$: Where the glycolate pathway continues.
$3$. $Mitochondria$: Where glycine is converted to serine, releasing $CO_2$.
Therefore, all three organelles are required for the process to complete.

(C) Photorespiration is a light-dependent process that occurs in $C_3$ plants.
It is initiated in the chloroplasts when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase,binding with $O_2$ instead of $CO_2$.
This process involves three organelles: the chloroplast,the peroxisome,and the mitochondria.
Unlike normal respiration,it does not produce $ATP$ or $NADPH$ and instead results in the loss of fixed carbon.

(A) Photorespiration is a wasteful process that occurs in $C_3$ plants.
In $C_3$ plants,the enzyme $RuBisCO$ has an affinity for both $CO_2$ and $O_2$.
When $O_2$ levels are high or $CO_2$ levels are low,$RuBisCO$ acts as an oxygenase,leading to the photorespiratory pathway.
$C_4$ and $CAM$ plants have evolved mechanisms to minimize photorespiration by concentrating $CO_2$ around the $RuBisCO$ enzyme,thereby suppressing its oxygenase activity.

(D) The metabolism of glycolate,also known as the photorespiratory pathway or $C_2$ cycle,occurs in three different cell organelles: chloroplasts,peroxisomes,and mitochondria.
Among the given options,peroxisomes are the primary site where glycolate is oxidized to glyoxylate by the enzyme glycolate oxidase.

(B) Photorespiration is a wasteful process that occurs in $C_3$ plants during photosynthesis. It happens when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase,binding with $O_2$ instead of $CO_2$. This process occurs in the chloroplasts,peroxisomes,and mitochondria. Therefore,it is closely associated with the light-dependent reactions of photosynthesis.

(A) The $C_2$ cycle is also known as photorespiration or the glycolate cycle.
In this process,the enzyme $RuBisCO$ acts as an oxygenase,leading to the formation of a two-carbon compound called phosphoglycolate.
This pathway involves the organelles chloroplasts,peroxisomes,and mitochondria.
Therefore,the correct option is $A$.

(B) Photorespiration is a wasteful process that occurs in plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
In $C_3$ plants,the concentration of $CO_2$ inside the leaf is relatively low,and $RuBisCO$ is exposed to high levels of $O_2$,which leads to the oxygenation of $RuBP$ and the initiation of the photorespiratory pathway.
$C_4$ plants and $CAM$ plants have evolved mechanisms to minimize photorespiration by concentrating $CO_2$ around the $RuBisCO$ enzyme,thereby suppressing its oxygenase activity.
Therefore,photorespiration is a characteristic feature primarily observed in $C_3$ plants.

(B) Photorespiration is a wasteful process that occurs in $C_3$ plants because the enzyme $RuBisCO$ has an affinity for both $CO_2$ and $O_2$. In $C_3$ plants,when $O_2$ levels are high,$RuBisCO$ binds with $O_2$ instead of $CO_2$,leading to photorespiration. $C_4$ plants have evolved a special mechanism (Kranz anatomy) to concentrate $CO_2$ around the $RuBisCO$ enzyme,which effectively eliminates photorespiration. Therefore,photorespiration is the key physiological difference between $C_3$ and $C_4$ plants.

(A) Photorespiration is a wasteful process that occurs in $C_3$ plants because the enzyme $RuBisCO$ has an affinity for both $CO_2$ and $O_2$.
In $C_4$ plants,photorespiration is absent or negligible.
This is because $C_4$ plants have a special mechanism to increase the concentration of $CO_2$ at the enzyme site in the bundle sheath cells.
This mechanism minimizes the oxygenase activity of $RuBisCO$,thereby preventing photorespiration.

(A) Photorespiration is a light-dependent process that occurs in $C_3$ plants.
It involves the cooperation of three specific cell organelles in a precise sequence.
$1$. The process begins in the $Chloroplast$, where $RuBisCO$ acts as an oxygenase, leading to the formation of phosphoglycolate.
$2$. The phosphoglycolate is then transported to the $Peroxisome$, where it is converted into glycine.
$3$. Finally, glycine is transported to the $Mitochondria$, where it is converted into serine, releasing $CO_2$ and $NH_3$.
Therefore, the correct sequence is $Chloroplast \rightarrow Peroxisome \rightarrow Mitochondria$.

(A) The 'Warburg effect' refers to the observation that the rate of photosynthesis in $C_3$ plants is inhibited by high concentrations of oxygen $(O_2)$.
This occurs because $O_2$ competes with $CO_2$ for the active site of the enzyme RuBisCO,leading to photorespiration instead of the Calvin cycle.
Therefore,the inhibitory effect is caused by high $O_2$ levels,which effectively reduces the efficiency of $CO_2$ fixation.

(D) Photorespiration is a wasteful process that occurs in $C_3$ plants when the enzyme RuBisCO acts as an oxygenase rather than a carboxylase.
This process is stimulated by conditions that favor the oxygenase activity of RuBisCO.
$1$. High temperature: As temperature increases,the affinity of RuBisCO for $CO_2$ decreases more rapidly than for $O_2$.
$2$. High $O_2$ concentration: $A$ high ratio of $O_2$ to $CO_2$ promotes the binding of $O_2$ to the active site of RuBisCO.
$3$. High light intensity: High light intensity often leads to increased internal $O_2$ levels due to rapid photolysis of water and increased temperatures,which indirectly stimulates photorespiration.
Therefore,all the given factors contribute to the stimulation of photorespiration.

(A) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
In this process,$RuBP$ (Ribulose$-1,5-$bisphosphate) reacts with $O_2$ to form one molecule of $3$-phosphoglycerate and one molecule of $2$-phosphoglycolate.
The $2$-phosphoglycolate is then dephosphorylated to form glycolate.
Therefore,glycolate is the primary substrate that enters the photorespiratory pathway (also known as the $C_2$ cycle) in the peroxisomes.

(B) Glycolate is the first product of photorespiration. Photorespiration occurs when the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase. This happens primarily under conditions of low $CO_2$ concentration and high $O_2$ concentration,often triggered by high temperatures and intense light. Therefore,glycolate accumulates in the chloroplast when $CO_2$ levels are low.

(D) In $C_3$ plants,the enzyme $RuBisCO$ (Ribulose$-1,5-$bisphosphate carboxylase-oxygenase) can act as both a carboxylase and an oxygenase.
When the concentration of $O_2$ is high and $CO_2$ is low,$RuBisCO$ binds with $O_2$ instead of $CO_2$.
This reaction of $RuBP$ (a $5$-carbon compound) with $O_2$ is the first step of photorespiration.
This reaction produces one molecule of $3$-phosphoglycerate and one molecule of $2$-phosphoglycolate.
Therefore,the process is initiated by the oxygenation of $RuBP$.

(C) Photorespiration is a wasteful process that occurs in $C_3$ plants because the enzyme $RuBisCO$ has an affinity for both $CO_2$ and $O_2$.
In $C_3$ plants,when $O_2$ concentration is high,$RuBisCO$ binds with $O_2$ instead of $CO_2$,leading to photorespiration.
This process involves three organelles: chloroplasts,peroxisomes,and mitochondria.
It occurs only in the presence of light (daytime).
$C_4$ plants have evolved a mechanism to minimize photorespiration by concentrating $CO_2$ around the $RuBisCO$ enzyme in bundle sheath cells,thus preventing $RuBisCO$ from binding with $O_2$.
Therefore,stating that photorespiration is a characteristic of $C_4$ plants is incorrect.

(B) Photorespiration,also known as the $C_2$ cycle,occurs when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
This process begins with the oxygenation of $RuBP$ (Ribulose$-1,5-$bisphosphate) to form one molecule of $3$-phosphoglycerate and one molecule of $2$-phosphoglycolate.
The $2$-phosphoglycolate is then dephosphorylated to form glycolate.
Therefore,glycolate acts as the primary substrate that enters the photorespiratory pathway in the peroxisomes.

(C) Photorespiration is a wasteful process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase.
During this process,$O_2$ is consumed (utilization of $O_2$),and $CO_2$ is released (production of $CO_2$).
However,unlike photosynthesis or cellular respiration,photorespiration does not result in the synthesis of $ATP$ or $NADPH$.
Therefore,the synthesis of $ATP$ is not observed in photorespiration.

(D) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
$RuBisCO$ has an affinity for both $CO_2$ and $O_2$.
When the concentration of $O_2$ is high and the concentration of $CO_2$ is low,$RuBisCO$ binds with $O_2$ to initiate the photorespiratory pathway.
This typically happens under conditions of high temperature and high light intensity,which lead to the closure of stomata,thereby reducing the internal $CO_2$ concentration and increasing the $O_2$ concentration within the leaf.

(C) The Warburg effect refers to the inhibition of the rate of photosynthesis in $C_3$ plants when the concentration of $O_2$ is high.
This occurs because $O_2$ competes with $CO_2$ for the active site of the enzyme $RuBisCO$.
When $O_2$ binds to $RuBisCO$, it initiates the process of photorespiration instead of the Calvin cycle, which reduces the overall efficiency of photosynthesis.

(C) The process described is $Photorespiration$ (also known as the $C_2$ cycle).
In $C_3$ plants,when the concentration of $O_2$ is high,the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase.
This process involves three organelles: the $Chloroplast$,the $Peroxisome$,and the $Mitochondria$.
Specifically,the oxygenation of $RuBP$ occurs in the $Chloroplast$ stroma,while subsequent reactions involving the conversion of glycolate to glycine and then to serine occur in the $Peroxisome$ and $Mitochondria$ respectively.
Therefore,the correct combination of organelles involved in the pathway that utilizes oxygen is the $Chloroplast$,$Peroxisome$,and $Mitochondria$.

(C) The $C_2$ cycle,also known as photorespiration,involves three organelles: chloroplasts,peroxisomes,and mitochondria. However,the primary metabolic reactions of the $C_2$ cycle (photorespiration) are predominantly associated with the peroxisome and mitochondria. The $C_3$ cycle,also known as the Calvin cycle,occurs exclusively in the stroma of the chloroplast. Therefore,the $C_2$ cycle is associated with peroxisomes and mitochondria,while the $C_3$ cycle is associated with the stroma of the chloroplast. Given the options provided,the most accurate association for the $C_2$ cycle and $C_3$ cycle locations is Peroxisome and Stroma.

(D) Photorespiration ($C_2$ cycle) occurs in $C_3$ plants where the enzyme $RuBisCO$ acts as an oxygenase. During this process,glycine is converted into serine in the mitochondria,which releases $NH_3$ (ammonia) and $CO_2$. Dark respiration (cellular respiration) also involves the breakdown of amino acids,which can release ammonia. $CAM$ plants also exhibit metabolic processes that can lead to the release of nitrogenous compounds. Therefore,$NH_3$ can be released in all these processes.

(A) Photorespiration,also known as the $C_2$ cycle or the glycolate pathway,was discovered by $Decker$ and $Tio$ in $1959$.
It is a light-dependent process in which oxygen is consumed and carbon dioxide is released by photosynthetic cells,leading to a loss of fixed carbon.

(B) Peroxisomes are specialized cell organelles that play a crucial role in various metabolic pathways.
In plants,peroxisomes are specifically associated with $Photorespiration$ (also known as the $C_2$ cycle).
During photorespiration,the enzyme $RuBisCO$ acts on $O_2$ instead of $CO_2$,leading to the production of phosphoglycolate.
This phosphoglycolate is transported to the peroxisome,where it is converted into glycine,which is then further processed in the mitochondria.
Therefore,peroxisomes are essential for the photorespiratory pathway.

(C) Photorespiration is a complex metabolic pathway that involves the cooperation of three distinct cell 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.
$2$. The phosphoglycolate is then transported to the peroxisome,where it is converted into glycine.
$3$. Finally,glycine is transported to the mitochondria,where it is converted into serine,releasing $CO_2$ and $NH_3$.
Among the given options,the peroxisome is the essential organelle involved in the photorespiratory pathway.

(A) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
In this process,the enzyme $RuBisCO$ reacts with $O_2$ instead of $CO_2$ to oxygenate $RuBP$ (Ribulose$-1,5-$bisphosphate).
This reaction produces one molecule of $3$-phosphoglycerate and one molecule of $2$-phosphoglycolate.
The $2$-phosphoglycolate is then dephosphorylated to form glycolate,which serves as the primary substrate for the photorespiratory pathway.
Therefore,glycolate is the substrate for photorespiration.

(C) Peroxisomes are specialized cell organelles that play a crucial role in various metabolic pathways. In plants,peroxisomes are specifically associated with $Photorespiration$ (also known as the $C_2$ cycle). During this process,they work in coordination with chloroplasts and mitochondria to metabolize phosphoglycolate,a byproduct of the oxygenase activity of $RuBisCO$.

(C) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
In this process,$RuBP$ (a $5$-carbon compound) reacts with $O_2$ instead of $CO_2$.
This reaction is known as oxygenation,which is the first step of the photorespiratory pathway.
As a result,$RuBP$ is converted into one molecule of $3$-phosphoglycerate ($3$-$PGA$) and one molecule of phosphoglycolate ($2$-carbon compound).

(A) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
In this process,the primary substrate is $2$-phosphoglycolate,which is formed when $RuBP$ reacts with $O_2$.
This $2$-phosphoglycolate is then dephosphorylated to form glycolate.
Therefore,glycolate is considered the primary substrate or intermediate involved in the photorespiratory pathway.

(A) The Warburg effect refers to the inhibition of photosynthesis in $C_3$ plants by high concentrations of oxygen $(O_2)$.
This phenomenon occurs because the enzyme RuBisCO has an affinity for both $CO_2$ and $O_2$.
When $O_2$ levels are high,RuBisCO catalyzes the oxygenation of RuBP instead of carboxylation,leading to photorespiration.
This process reduces the efficiency of photosynthesis,hence the Warburg effect is directly associated with the concentration of $O_2$.

(A) Photorespiration is considered a wasteful process because it does not produce $ATP$ or $NADPH$. Instead,it consumes $ATP$ and releases $CO_2$ that was previously fixed by the Calvin cycle. This process occurs when the enzyme $RuBisCO$ acts as an oxygenase rather than a carboxylase,leading to the oxidation of $RuBP$.

(D) Photorespiration is a metabolic pathway that occurs in photosynthetic plants when the enzyme $RuBisCO$ acts on oxygen instead of carbon dioxide.
This process involves the coordinated activity of three organelles: the chloroplast,the peroxisome,and the mitochondria.
Among the given options,peroxisomes are the primary organelles where the conversion of glycolate to glyoxylate and subsequently to glycine occurs during the photorespiratory pathway.
Therefore,peroxisomes are directly associated with photorespiration.