C3 and Dark reaction Questions in English

(D) In the Calvin cycle,the primary carboxylation step involves the enzyme $RuBisCO$,which catalyzes the reaction of $CO_2$ with Ribulose $1, 5$-bisphosphate $(RuBP)$.
This reaction produces an unstable $6$-carbon intermediate compound.
This unstable compound immediately undergoes hydrolysis to form two molecules of $3$-phosphoglyceric acid ($3$-$PGA$).
Therefore,$3$-$PGA$ is the first stable intermediate product of the Calvin cycle.

(B) In the Calvin cycle,the enzyme $RuBisCO$ catalyzes the carboxylation of $RuBP$ (Ribulose $1,5$-bisphosphate) with $CO_2$.
This reaction produces an unstable $6$-carbon intermediate compound known as $2$-carboxy,$3$-keto,$1,5$-biphospho ribitol.
This intermediate immediately undergoes hydrolysis to form two molecules of $3$-phosphoglycerate ($3$-$PGA$).

(A) In the process of carbon dioxide reduction (which occurs during the Calvin cycle in photosynthesis),$ATP$ is consumed to provide the necessary energy for the conversion of $3$-phosphoglycerate to glyceraldehyde-$3$-phosphate.
Therefore,$ATP$ is used in this process.

(B) In the Calvin cycle of photosynthesis,the reduction phase involves the conversion of $3$-phosphoglyceric acid $(PGA)$ into glyceraldehyde-$3$-phosphate (also known as phosphoglyceraldehyde).
This step requires $ATP$ and $NADPH$ produced during the light-dependent reactions.
Specifically,the carboxyl group of $PGA$ is reduced to an aldehyde group in phosphoglyceraldehyde,which is a reduction process.

(B) The dark reaction of photosynthesis is also known as the $C_3$ cycle or the Calvin cycle.
It is called the 'dark reaction' not because it occurs in the dark,but because it is light-independent.
This means that the reactions involved in the fixation of $CO_2$ into carbohydrates do not directly require light energy,although they depend on the products of the light-dependent reactions ($ATP$ and $NADPH$).
Therefore,it does not require the presence of light to proceed.

(A) The enzyme Ribulose bisphosphate carboxylase,commonly known as $RuBisCO$,is the most abundant enzyme on Earth.
It catalyzes the first step of the Calvin cycle,which is the carboxylation of Ribulose $1, 5$-bisphosphate $(RuBP)$.
In this reaction,$CO_2$ is fixed by combining with $RuBP$ to form two molecules of $3$-phosphoglyceric acid $(3-PGA)$.
Therefore,the carboxylation reaction occurs between $CO_2$ and Ribulose $1, 5$-bisphosphate.

(A) In the Calvin cycle,the synthesis of one molecule of glucose $(C_6H_{12}O_6)$ requires $6$ turns of the cycle.
Each turn of the Calvin cycle involves the fixation of one molecule of $CO_2$.
For every $CO_2$ molecule fixed,$3$ $ATP$ and $2$ $NADPH$ are consumed in the reduction and regeneration phases.
Specifically,in the regeneration phase of $RuBP$,$1$ $ATP$ is consumed per $CO_2$ molecule fixed.
Since $6$ molecules of $CO_2$ are required to produce $1$ molecule of glucose,the total $ATP$ required for the regeneration phase is $6 \times 1 = 6$ $ATP$ molecules.

(A) The dark reaction of photosynthesis,also known as the $Calvin$ cycle,begins with the fixation of atmospheric $CO_2$.
This process is catalyzed by the enzyme $RuBisCO$,which facilitates the attachment of $CO_2$ to a $5$-carbon sugar called $Ribulose$ $1,5$-bisphosphate $(RuBP)$.
This specific step,where $CO_2$ is incorporated into an organic molecule,is known as $Carboxylation$.
Therefore,$Carboxylation$ is the first and most crucial step of the dark reaction.

(C) The Calvin cycle involves the fixation of $CO_2$ into organic compounds.
Each turn of the Calvin cycle fixes one molecule of $CO_2$ into a $3$-carbon compound ($3$-$PGA$).
Since a molecule of glucose $(C_6H_{12}O_6)$ contains $6$ carbon atoms,it requires the fixation of $6$ molecules of $CO_2$.
Therefore,$6$ turns of the Calvin cycle are necessary to produce one molecule of glucose.

(B) In the Calvin cycle ($C_3$ cycle),the fixation of $1$ molecule of $CO_2$ requires $3$ molecules of $ATP$ and $2$ molecules of $NADPH$.
Specifically,$2$ $ATP$ are used during the reduction phase and $1$ $ATP$ is used during the regeneration phase of $RuBP$.
Therefore,for the fixation of $1$ $CO_2$,the requirement is $3$ $ATP$ and $2$ $NADPH$.

(C) The enzyme $RUBP$ carboxylase (also known as $RuBisCO$) is the most abundant protein in the world. It is found in high concentrations within the stroma of chloroplasts in photosynthetic plants,where it catalyzes the first step of the Calvin cycle (carbon fixation).

(D) In the $C_3$ cycle (Calvin cycle) of photosynthesis,the primary acceptor of atmospheric $CO_2$ is a $5$-carbon ketose sugar called Ribulose-$1,5$-bisphosphate $(RuBP)$.
This reaction is catalyzed by the enzyme Ribulose-$1,5$-bisphosphate carboxylase-oxygenase $(RuBisCO)$,which is the most abundant protein on Earth.
The fixation of $CO_2$ with $RuBP$ results in the formation of two molecules of $3$-phosphoglycerate ($3$-$PGA$).

(A) In $C_3$ plants,the primary carboxylation step involves the enzyme $RuBisCO$,which catalyzes the reaction between $CO_2$ and Ribulose-$1, 5$-bisphosphate $(RuBP)$.
This reaction results in the formation of two molecules of $3$-phosphoglyceric acid ($3$-$PGA$).
Since $3$-$PGA$ is a $3$-carbon compound and is the first stable product formed in the Calvin cycle,these plants are referred to as $C_3$ plants.

(D) The Calvin cycle (also known as the $C_3$ cycle) is a light-independent reaction of photosynthesis.
In the Calvin cycle,$3$ molecules of $CO_2$ are fixed to produce one molecule of $Glyceraldehyde-3-phosphate$ $(G3P)$.
To produce one molecule of glucose $(C_6H_{12}O_6)$,the cycle must turn $6$ times,fixing $6$ molecules of $CO_2$.
Water $(H_2O)$ is primarily consumed during the light-dependent reactions (photolysis) to provide electrons,protons,and oxygen,not directly within the Calvin cycle itself.
However,if the question refers to the stoichiometry of the overall photosynthetic equation $(6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O)$,the net consumption of water for the synthesis of one glucose molecule is $12$ molecules.
Since the Calvin cycle is the dark reaction phase,it does not directly consume water molecules. However,in the context of standard textbook questions regarding the stoichiometry of the cycle's input for glucose synthesis,the answer is often considered $0$ for the cycle itself,but if the question implies the water required for the light reactions to support the fixation of $3$ $CO_2$ molecules (half a glucose),the answer is $6$ $H_2O$ molecules.

(B) $CO_2$ compensation point is the concentration of $CO_2$ at which the rate of photosynthesis exactly equals the rate of respiration.
$C_3$ plants have a higher $CO_2$ compensation point (approximately $25-100 \ ppm$) because they undergo photorespiration,which releases $CO_2$ and reduces the net photosynthetic efficiency.
In contrast,$C_4$ plants have a very low $CO_2$ compensation point (approximately $0-10 \ ppm$) because they possess a mechanism to concentrate $CO_2$ around the enzyme $RuBisCO$,effectively suppressing photorespiration.
Therefore,$C_3$ plants exhibit a higher $CO_2$ compensation point compared to $C_4$ plants.

(B) The temperature coefficient $(Q_{10})$ is defined as the ratio of the rate of a reaction at two temperatures differing by $10^{\circ}C$.
For most biological reactions,including the dark reaction (Calvin cycle) of photosynthesis,the $Q_{10}$ value typically ranges between $2$ and $3$.
This indicates that the rate of the reaction approximately doubles or triples with every $10^{\circ}C$ rise in temperature,provided the enzymes are not denatured.

(C) Photorespiration is a process that occurs in $C_3$ plants when the enzyme $RuBisCO$ acts as an oxygenase instead of a carboxylase.
Despite this process,the primary pathway for the fixation of atmospheric $CO_2$ in all photosynthetic plants (including those undergoing photorespiration) remains the Calvin cycle ($C_3$ cycle).
In the Calvin cycle,$CO_2$ is fixed by the enzyme $RuBisCO$ to form $3$-phosphoglycerate ($3$-$PGA$).

(D) In $C_3$ plants,the primary carboxylation step involves the enzyme $RuBisCO$,which catalyzes the reaction of $CO_2$ with $RuBP$ ($5$-carbon sugar).
This reaction results in the formation of two molecules of $3$-phosphoglyceric acid ($3$-$PGA$),which is a $3$-carbon compound.
Since the first stable product formed is a $3$-carbon molecule,these plants are referred to as $C_3$ plants.
Therefore,the correct option is $D$.

(C) In the $C_3$ cycle (Calvin cycle),the regeneration phase involves the formation of $Sedoheptulose-1,7-bisphosphate$ $(SHDP)$ from $Erythrose-4-phosphate$ and $Xylulose-5-phosphate$.
$Sedoheptulose-1,7-bisphosphate$ $(SHDP)$ is a $7$-carbon sugar phosphate intermediate.
$SHP$ stands for $Sedoheptulose-7-phosphate$,which is also a $7$-carbon compound,but $SHDP$ is specifically recognized as the bisphosphate intermediate in the pathway.
Therefore,$SHDP$ is the correct $7$-carbon compound mentioned in the context of the $C_3$ cycle reactions.

(C) Rubisco (Ribulose bisphosphate carboxylase-oxygenase) is the most abundant enzyme in the world. It is found in the stroma of chloroplasts and plays a crucial role in the Calvin cycle during photosynthesis. It accounts for approximately $16\%$ of the total chloroplast protein.

(C) In the process of photosynthesis,specifically during the Calvin cycle ($C_3$ cycle),the first step involves the carboxylation of Ribulose-$1,5$-bisphosphate $(RuBP)$.
This reaction is catalyzed by the enzyme RuBisCO,where $CO_2$ is fixed to form a $3$-carbon compound known as $3$-phosphoglyceric acid ($3$-$PGA$).
This $3$-$PGA$ is the first stable intermediate product formed in the light-independent reactions of photosynthesis.

(B) The dark reaction of photosynthesis,also known as the Calvin cycle or light-independent reaction,occurs in the stroma of the chloroplast.
During this process,the energy stored in $ATP$ and $NADPH$ (produced during the light reaction) is used to fix atmospheric $CO_2$ into organic compounds like glucose.
Photolysis of water and activation of chlorophyll are events associated with the light-dependent reaction,not the dark reaction.
Therefore,the correct statement is that $CO_2$ is reduced to organic compounds.

(D) In the $C_3$ cycle (Calvin cycle),the synthesis of one molecule of glucose $(C_6H_{12}O_6)$ requires $6$ turns of the cycle.
Each turn of the Calvin cycle requires $3 \ ATP$ and $2 \ NADPH$.
Therefore,for $6$ turns: $6 \times 3 = 18 \ ATP$ and $6 \times 2 = 12 \ NADPH$.
Since $1 \ NADPH$ is equivalent to $3 \ ATP$ in terms of energy,$12 \ NADPH = 12 \times 3 = 36 \ ATP$.
Total energy required = $18 \ ATP + 36 \ ATP = 54 \ ATP$ equivalents.

(A) In the Calvin cycle of photosynthesis,the primary acceptor of $CO_2$ is a $5$-carbon compound called Ribulose-$1,5$-bisphosphate $(RuBP)$.
This reaction is catalyzed by the enzyme $RuBisCO$ (Ribulose-$1,5$-bisphosphate carboxylase-oxygenase).
The combination of $CO_2$ with $RuBP$ results in the formation of two molecules of $3$-phosphoglycerate ($3$-$PGA$).

(C) The process of photosynthesis occurs in two main stages: the light-dependent reaction and the light-independent reaction (also known as the dark reaction or Calvin cycle).
In the light-dependent reaction,light energy is captured to produce $ATP$ and $NADPH$.
In the dark reaction (Calvin cycle),the $ATP$ and $NADPH$ produced in the light reaction are used to reduce $CO_2$ into carbohydrates (sugars).
Therefore,the reduction of $CO_2$ to form sugar is a characteristic feature of the dark reaction.

(B) The path of carbon in the dark reaction (Calvin cycle) of photosynthesis was traced by Melvin Calvin and his colleagues.
They used the radioactive isotope of carbon,$C^{14}$,in algal photosynthesis studies.
By using $C^{14}O_2$,they were able to identify the intermediate compounds formed during the fixation of carbon dioxide,leading to the discovery of the Calvin cycle.

(D) Melvin Calvin and his colleagues used radioactive $ ^{14}C $ in algal photosynthesis studies to discover the Calvin cycle. They specifically used unicellular green algae,$ Chlorella $ and $ Scenedesmus $,to trace the path of carbon during the dark reactions of photosynthesis. Therefore,$ Chlorella $ is the correct answer.

(D) The chloroplast is a double-membrane organelle.
Inside the chloroplast,the fluid-filled space is called the stroma.
The stroma contains enzymes required for the synthesis of carbohydrates and proteins.
These enzymes are responsible for the light-independent reactions (also known as the Calvin cycle or dark reactions) of photosynthesis.
Chlorophyll is located in the thylakoid membranes,not the stroma.
Ribosomes are present in the stroma,but the primary functional characteristic related to the metabolic pathway of photosynthesis in the stroma is the presence of light-independent reaction enzymes.

(A) The process of photosynthesis occurs in two main stages: the light-dependent reaction and the light-independent reaction (also known as the dark reaction or $C_3$ cycle).
$1$. The light-dependent reactions occur in the thylakoid membranes (grana) of the chloroplast,where light energy is converted into chemical energy ($ATP$ and $NADPH$).
$2$. The dark reaction (Calvin cycle) takes place in the stroma of the chloroplast.
$3$. In the stroma,the $ATP$ and $NADPH$ produced during the light reaction are used to fix $CO_2$ into carbohydrates (sugars).
Therefore,the stroma is the primary site for the dark reaction.

(B) During photosynthesis,the overall reaction is $6CO_2 + 12H_2O \rightarrow C_6H_{12}O_6 + 6H_2O + 6O_2$.
Radioactive isotope studies (using $^{18}O$) have shown that the oxygen released during photosynthesis comes from water $(H_2O)$.
However,the oxygen atoms present in the glucose $(C_6H_{12}O_6)$ molecule are derived from the carbon dioxide $(CO_2)$ molecules used during the Calvin cycle.
Therefore,the oxygen in glucose comes from $CO_2$.

(A) Chloroplasts are the sites of photosynthesis in plants.
During the process of photosynthesis,the light-independent reactions (also known as the Calvin cycle) occur in the stroma of the chloroplast.
In this cycle,the enzyme RuBisCO facilitates the fixation of atmospheric $CO_2$ (carbon dioxide) into organic compounds like glucose.
Therefore,chloroplasts are responsible for the fixation of carbon dioxide.

(C) $RuBisCO$ (Ribulose bisphosphate carboxylase-oxygenase) is the most abundant enzyme in the world.
It is the key enzyme involved in the $C_3$ cycle (Calvin cycle) of photosynthesis.
The Calvin cycle takes place in the stroma of the chloroplasts in photosynthetic plants.
Therefore,$RuBisCO$ is located within the chloroplasts.

(C) In $C_3$ plants,the primary acceptor of $CO_2$ is Ribulose $1,5$-bisphosphate $(RuBP)$.
The enzyme RuBisCO catalyzes the carboxylation reaction where $CO_2$ combines with $RuBP$ to form two molecules of $3$-phosphoglyceric acid $(3-PGA)$.
Since the first stable product formed is a $3$-carbon compound $(3-PGA)$,these plants are called $C_3$ plants.
Therefore,the correct option is $C$.

(B) In the $C_3$ cycle (Calvin cycle),the fixation of $6$ molecules of $CO_2$ is required to produce one molecule of glucose $(C_6H_{12}O_6)$.
For the fixation of each molecule of $CO_2$,$3$ $ATP$ and $2$ $NADPH_2$ are consumed.
Therefore,for $6$ molecules of $CO_2$:
$ATP$ required = $6 \times 3 = 18$ $ATP$.
$NADPH_2$ required = $6 \times 2 = 12$ $NADPH_2$.
Thus,the correct answer is $18$ $ATP$ and $12$ $NADPH_2$.

(B) In the process of photosynthesis, the light-dependent reactions produce $ATP$ and $NADPH$, which are then used in the light-independent reactions (Calvin cycle) for the reduction of $CO_2$ into carbohydrates.
Therefore, during the reduction of $CO_2$ in the Calvin cycle, $ATP$ is consumed to provide the necessary energy for the conversion of $3-phosphoglycerate$ to $glyceraldehyde-3-phosphate$.

(D) Melvin Calvin and his colleagues conducted research on the path of carbon in photosynthesis using radioactive $ ^{14}C $ in algal photosynthesis studies. They specifically used unicellular green algae, $ Chlorella $ and $ Scenedesmus $, to trace the carbon fixation pathway, which eventually led to the discovery of the Calvin cycle.

(C) The $Calvin$ cycle,also known as the $C_3$ cycle or light-independent reactions,occurs in the stroma of the chloroplast.
In the stroma,the enzyme $RuBisCO$ facilitates the fixation of $CO_2$ into organic molecules using the $ATP$ and $NADPH$ produced during the light-dependent reactions.
Therefore,the correct site for the $Calvin$ cycle is the chloroplast.

(B) The $C_3$ cycle,also known as the Calvin cycle,is a series of light-independent reactions that take place in the stroma of chloroplasts during photosynthesis.
This cycle was discovered by Melvin Calvin,Andrew Benson,and James Bassham at the University of California,Berkeley.
Therefore,the credit for identifying the $C_3$ cycle goes to $M$. Calvin.

(B) Melvin Calvin used radioactive $ ^{14}C $ in algal photosynthesis studies.
He used radioactive chromatography to separate and identify the various intermediate compounds formed during the Calvin cycle.
This technique allowed him to trace the path of carbon in photosynthesis,leading to the discovery of the $ C_3 $ cycle.

(B) Melvin Calvin used radioactive $ ^{14}C $ in algal photosynthesis studies.
To separate and identify the various radioactive intermediate compounds formed during the Calvin cycle, he employed the technique of paper chromatography.
Following this, he used autoradiography to detect the radioactive spots on the chromatogram.

(D) The dark reaction (Calvin cycle) of photosynthesis occurs in the stroma of the chloroplast,not in the matrix of the mitochondria.
Therefore,Assertion $A$ is false.
Mitochondria are indeed the sites of aerobic respiration and are associated with energy metabolism ($ATP$ production),making Reason $R$ true.
Thus,the correct option is $D$.

(D) The dark reaction of photosynthesis,also known as the $Calvin$ cycle or light-independent reaction,takes place in the $Stroma$ of the chloroplast.
In the $Stroma$,enzymes are present that catalyze the fixation of $CO_2$ into carbohydrates using the $ATP$ and $NADPH$ produced during the light-dependent reactions.
$Grana$ and $Intergranal$ $lamellae$ are the sites for light-dependent reactions.

(D) The chloroplast consists of two main parts: the thylakoids and the stroma.
$1$. The thylakoids contain chlorophyll and are the site of the light-dependent reactions.
$2$. The stroma is the fluid-filled matrix of the chloroplast.
$3$. The stroma contains enzymes required for the synthesis of carbohydrates,which is known as the dark reaction or the Calvin cycle (light-independent reaction).
$4$. Therefore,the stroma contains the enzymes for the dark reaction.

(B) The dark reaction (also known as the Calvin cycle or light-independent reaction) of photosynthesis occurs in the stroma of the chloroplast.
This process involves the fixation of $CO_2$ into carbohydrates using the $ATP$ and $NADPH$ produced during the light-dependent reactions.
The enzymes required for the Calvin cycle,such as $RuBisCO$,are present in the stroma matrix,which provides the necessary environment for these biochemical reactions to take place.

(D) The stroma is the fluid-filled matrix of the chloroplast.
It contains enzymes required for the synthesis of carbohydrates and proteins.
The reactions that occur in the stroma are known as dark reactions or the Calvin cycle,which are light-independent.
Therefore,the stroma contains the enzymes necessary for these dark reactions.

(D) The chloroplast is a double-membrane organelle. The fluid-filled space inside the inner membrane is called the stroma.
The stroma contains enzymes required for the synthesis of carbohydrates and proteins,which are the light-independent reactions (also known as the Calvin cycle or dark reactions).
Chlorophyll and enzymes for light-dependent reactions are located in the thylakoid membranes.
Therefore,the correct option is $D$.

(A) $PGAL$ stands for Phosphoglyceraldehyde. It is a three-carbon sugar phosphate that acts as a key intermediate in metabolic pathways such as glycolysis and the Calvin cycle. During glycolysis,glucose is broken down into two molecules of $PGAL$ (also known as Glyceraldehyde$-3-$phosphate or $G3P$).

(D) During the dark reaction (Calvin cycle) of photosynthesis,the primary product synthesized is $3$-phosphoglyceraldehyde ($PGAL$ or $G3P$).
$1$. The Calvin cycle involves the fixation of $CO_2$ into organic compounds.
$2$. The enzyme $RuBisCO$ catalyzes the carboxylation of $RuBP$ to form $3$-phosphoglycerate ($3$-$PGA$).
$3$. Through a series of reduction reactions using $ATP$ and $NADPH$,$3$-$PGA$ is converted into $3$-phosphoglyceraldehyde $(PGAL)$,which is a triose sugar.
$4$. This $PGAL$ molecule serves as the precursor for the synthesis of glucose and other carbohydrates.

(D) During the dark reaction of photosynthesis (Calvin cycle),the primary product of the reduction phase is $3$-phosphoglyceraldehyde $(PGAL)$,which is a phosphorylated aldotriose sugar.
$PGAL$ (also known as glyceraldehyde-$3$-phosphate or $G3P$) is a $3$-carbon sugar phosphate that serves as the precursor for the synthesis of glucose and other carbohydrates.
$DHAP$ (dihydroxyacetone phosphate) is a ketotriose,while $PGAL$ is an aldotriose.

(B) $RUBISCO$ stands for Ribulose$-1,5-$bisphosphate carboxylase-oxygenase.
It is an enzyme present in the chloroplast stroma of photosynthetic plants.
It plays a crucial role in the Calvin cycle by catalyzing the carboxylation of ribulose$-1,5-$bisphosphate $(RuBP)$ with $CO_2$.