Mix Examples- Photosynthesis in Higher Plants Questions in English

(D) Photosynthetic microorganisms (such as cyanobacteria and certain algae) perform photosynthesis,which involves the conversion of solar energy into chemical energy stored in the form of organic compounds (like glucose).
During certain metabolic processes or under specific conditions,some photosynthetic microorganisms can also produce hydrogen gas.
Since they synthesize organic molecules,they effectively store chemical energy.
Therefore,all the given statements are correct.

(B) The correct matching is as follows:
$i.$ Mitochondrial matrix is the site of the Krebs cycle $(r)$.
$ii.$ Chloroplast stroma is the site of the dark reaction $(s)$.
$iii.$ Cristae are the sites of oxidative phosphorylation $(q)$.
$iv.$ Granum is the site of photophosphorylation $(p)$.
Therefore, the correct sequence is $i-r, ii-s, iii-q, iv-p$.

(C) Plants are autotrophic organisms that produce their own food through the process of $Photosynthesis$.
During $Photosynthesis$,plants convert light energy into chemical energy using $CO_2$ and $H_2O$.
Additionally,plants obtain essential minerals and water from the soil through the process of $Absorption$ via their root systems.
Therefore,the overall nutritional process involves both the synthesis of organic food and the absorption of inorganic nutrients.

(A) Plants are primarily autotrophic because they possess chlorophyll,which allows them to synthesize their own food through the process of photosynthesis. However,some plants exhibit heterotrophic nutrition,such as parasitic plants (e.g.,Cuscuta) or insectivorous plants (e.g.,Venus flytrap). Therefore,while autotrophic is the main mode,plants can exhibit both modes of nutrition.

(C) In plants,carbohydrates are synthesized during photosynthesis and are stored in the form of starch. Starch is a polysaccharide composed of glucose units and serves as the primary energy storage molecule in plants. Cellulose is a structural component of the cell wall,lignin provides mechanical support,and fructose is a simple sugar.

(B) Statement $P$ is incorrect because the primary product of the Calvin cycle (dark reaction) is glyceraldehyde$-3-$phosphate,which is an aldotriose,not a ketotriose.
Statement $Q$ is incorrect because the sugar present in $ATP$ is ribose,which is an aldopentose,not a ketopentose.

(B) Statement $P$ is false because during the dark reaction (Calvin cycle) of photosynthesis,the primary sugar synthesized is a triose phosphate (glyceraldehyde $3$-phosphate),which is an aldose sugar,not a ketotriose.
Statement $Q$ is false because the sugar present in the structure of $ATP$ is ribose. Ribose is an aldopentose sugar,not a ketopentose sugar.
Therefore,both statements $P$ and $Q$ are false.

(A) $Rhodospirillum$ is a purple non-sulfur bacterium that performs anoxygenic photosynthesis.
In this process,organic compounds or other substances (like $H_2S$) are used as electron donors instead of water $(H_2O)$.
Since water is not used as the electron donor,oxygen $(O_2)$ is not evolved as a byproduct.
In contrast,$Spirogyra$,$Chlamydomonas$,and $Ulva$ are algae that perform oxygenic photosynthesis,where water is the electron donor and oxygen is released during the photolysis of water.

(A) : $Oscillatoria$ is a filamentous Gram-negative cyanobacterium that performs oxygenic photosynthesis due to the presence of chlorophyll-$a$,similar to eukaryotic algae and higher plants.
In contrast,$Rhodospirillum$,$Chlorobium$,and $Chromatium$ are photosynthetic bacteria that perform anoxygenic photosynthesis,as they use electron donors other than water (such as $H_2S$).

(A) Photosynthesis is a biological process in which green plants,algae,and some bacteria use $CO_2$ and water to produce glucose and oxygen.
Therefore,photosynthesis acts as a sink for $CO_2$ and removes it from the atmosphere,rather than adding it.
In contrast,the burning of wood,the burning of fossil fuels,and volcanic activity are all processes that release $CO_2$ into the atmosphere.

(A) Photosynthesis is the primary process by which autotrophs (plants,algae,and some bacteria) convert solar energy into chemical energy.
According to standard ecological estimates,approximately $4 \times 10^{13} \ kg$ of carbon is fixed in the biosphere through the process of photosynthesis annually.
This carbon fixation is a critical component of the global carbon cycle,as it removes $CO_2$ from the atmosphere and incorporates it into organic compounds.

(A) Option $A$ is correct. Stroma lamellae membranes lack both $PSII$ and $NADP$ reductase enzyme,which is why they only perform cyclic photophosphorylation.
Option $B$ is incorrect because $F_1$ is the headpiece that protrudes into the stroma,while $F_0$ is embedded in the membrane.
Option $C$ is incorrect because $T.W.$ Engelmann used Cladophora algae,not Chlamydomonas.
Option $D$ is incorrect because the $C_4$ pathway starts with the carboxylation of $PEP$ (phosphoenolpyruvate) to form oxaloacetic acid,not decarboxylation.

(A) The light reaction of photosynthesis occurs in the thylakoid membranes (membranous system) of the chloroplast and results in the production of $ATP$ and $NADPH$.
Therefore,$A$ matches with $1$ and $2$.
The dark reaction (Calvin cycle) occurs in the stroma of the chloroplast and leads to the synthesis of sugars,which are stored as starch.
Therefore,$B$ matches with $3$.
Thus,the correct matching is $A-1, 2$ and $B-3$.

(D) The correct matches are as follows:
$A$. $PGA$ (Phosphoglyceric acid) is the first stable product of the $C_3$ pathway $(A-S)$.
$B$. $OAA$ (Oxaloacetic acid) is the first stable product of the $C_4$ pathway $(B-R)$.
$C$. RuBisCO acts as an oxygenase enzyme during photorespiration $(C-P)$.
$D$. RuBP (Ribulose bisphosphate) is the primary acceptor of $CO_2$ in the Calvin cycle $(D-Q)$.
Therefore,the correct sequence is $A-S, B-R, C-P, D-Q$,which corresponds to option $D$.

(D) In photosynthesis,pigments are classified based on their roles and properties:
$1$. Chlorophyll-$a$ acts as the primary pigment and is the main component of the reaction centre in photosystems.
$2$. Chlorophyll-$a$ appears bright or blue-green in the chromatogram.
$3$. Carotenoids include carotenes and xanthophylls,which appear yellow to yellow-orange in colour.
Since all the given statements accurately describe the properties of these photosynthetic pigments,the correct option is $D$.

(A) The correct matches are as follows:
$(1)$ Cyclic photophosphorylation involves only $PS-I$ and results in the synthesis of $ATP$. Thus,$(1-a)$ and $(1-b)$ are relevant,but in the context of the given options,$(1-a)$ is the primary characteristic.
$(2)$ Non-cyclic photophosphorylation involves both $PS-I$ and $PS-II$,leading to the formation of $ATP$ and $NADPH$. Among the choices,$(2-b)$ is a common outcome.
$(3)$ $C_4$ cycle is an adaptation in plants to minimize photorespiration,which leads to high productivity compared to $C_3$ plants. Thus,$(3-d)$ is the correct match.
Matching these: $(1-a)$,$(2-b)$,and $(3-d)$ corresponds to option $A$.

(D) $(i).$ In $C_4$ plants,the primary $CO_2$ acceptor is Phosphoenolpyruvate $(PEP)$,which is a $3$-carbon compound. This statement is correct.
$(ii).$ In the process of photosynthesis,$PS-II$ absorbs light energy at $680 \ nm$ $(P_{680})$. This statement is correct.
$(iii).$ The $P_{680}$ chlorophyll system is part of $PS-II$,not $PS-I$. $PS-I$ contains $P_{700}$. Therefore,this statement is incorrect.
Thus,statements $(i)$ and $(ii)$ are correct.

(D) $C_4$ plants are more productive than $C_3$ plants because they possess a mechanism to minimize photorespiration,which is a wasteful process that reduces the efficiency of carbon fixation.
Therefore,the statement $A$ is false because $C_3$ plants have lower productivity compared to $C_4$ plants.
Photorespiration is a process that occurs in $C_3$ plants due to the oxygenase activity of the enzyme $RuBisCO$,which binds to $O_2$ instead of $CO_2$ under certain conditions.
Thus,the statement $R$ is true.
Hence,the correct option is $D$.

(A) In the Calvin cycle,the enzyme $RuBisCO$ catalyzes the carboxylation of $RuBP$ (Ribulose $1,5$-bisphosphate) with $CO_2$ to form $3$-phosphoglycerate.
In photorespiration,the same enzyme $RuBisCO$ acts as an oxygenase,catalyzing the oxygenation of $RuBP$ with $O_2$ instead of $CO_2$,leading to the production of one molecule of phosphoglycerate and one molecule of phosphoglycolate.
Both statements $A$ and $R$ are scientifically correct.

(C) Photosynthesis is the biological process by which green plants,algae,and some bacteria convert light energy into chemical energy.
During this process,plants take in $CO_2$ from the atmosphere and release $O_2$ as a byproduct.
The overall chemical equation for photosynthesis is: $6CO_2 + 12H_2O \xrightarrow{\text{Light}} C_6H_{12}O_6 + 6O_2 + 6H_2O$.
Therefore,the correct option is $C$.

(B) Photosynthesis is a process that occurs in chloroplasts ($A$ is correct).
It is primarily a light-dependent process,but the term 'photosynthesis' encompasses both light and dark reactions (Calvin cycle). While light reactions require light,the dark reactions can occur in the absence of light,provided the products of the light reaction ($ATP$ and $NADPH$) are available. Therefore,stating it occurs 'only' during the daytime is scientifically inaccurate ($B$ is incorrect).
Photosynthesis is a fundamental process found in both $C_3$ and $C_4$ plants ($C$ and $D$ are correct descriptions of photosynthetic pathways).

(A) The correct matches are as follows:
$1$. $(p)$ Grana region of chloroplast is the site for the Light reaction of photosynthesis.
$2$. $(q)$ Stroma region of chloroplast is the site for the Dark reaction (Calvin cycle) of photosynthesis.
$3$. $(r)$ Cytoplasm is the site for Glycolysis,which is the first step of cellular respiration.
$4$. $(s)$ Matrix of mitochondria is the site for the Krebs cycle ($TCA$ cycle).
Therefore,the correct sequence is $(p-ii), (q-iii), (r-iv), (s-i)$.

(B) Statement $(1)$ is correct: The chloroplast consists of a membranous system of grana and a fluid stroma.
Statement $(2)$ is incorrect: Pigments (chlorophylls and carotenoids) are present in the thylakoid membranes of the grana,not in the stroma.
Statement $(3)$ is incorrect: In the stroma,enzymatic reactions incorporate $CO_2$ (not $O_2$) into the plant,leading to the synthesis of sugar.
Statement $(4)$ is correct: The formation of sugar in the stroma (Dark reaction or Calvin cycle) does not directly require light,although it depends on the products of the light reaction ($ATP$ and $NADPH$).
Since statements $(2)$ and $(3)$ are incorrect,the correct option is $B$.

(D) Assertion $(A)$ is incorrect because the process of trapping light energy and synthesizing $ATP$ and $NADPH$ is known as the light reaction,not the dark reaction.
Reason $(R)$ is correct because the stroma contains enzymes that perform the Calvin cycle,which incorporates $CO_2$ into organic compounds to synthesize sugar. This process is known as the dark reaction or light-independent reaction.

(B) $A-$ The statement is incorrect because enzymatic reactions in the stroma synthesize sugars (glucose),which are then stored as starch. The original statement incorrectly mentions protein synthesis as the primary product of the Calvin cycle.
$R-$ The statement is incorrect because the membrane system of the chloroplast (thylakoids) is specifically responsible for trapping light energy and synthesizing $ATP$ and $NADPH$ during the light-dependent reactions.
Therefore,both $A$ and $R$ are incorrect.

(B) Photosynthesis is the process by which green plants,algae,and certain bacteria convert light energy into chemical energy.
While terrestrial plants are visible,the vast majority of photosynthesis on Earth occurs in aquatic environments.
Marine algae (phytoplankton) are responsible for approximately $85-90\%$ (or $9/10$) of the total global photosynthesis.
Therefore,the correct option is $B$.

(A) $1$. $C_3$ plants are those that fix $CO_2$ into a $3$-carbon compound $(PGA)$. Maize is a $C_4$ plant,not a $C_3$ plant. Thus,the pair '$C_3$ - Maize' is incorrect.
$2$. $C_4$ plants exhibit Kranz anatomy,which is a correct association.
$3$. The Calvin cycle involves the formation of $3$-phosphoglyceric acid $(PGA)$ as the first stable product,which is correct.
$4$. The Hatch and Slack pathway is another name for the $C_4$ cycle. However,the pathway involves oxaloacetic acid $(OAA)$ as the first stable product,not acetic acid. Therefore,both options $A$ and $D$ contain incorrect information. Given the standard context of such questions,$C_3$ - Maize is a classic example of a mismatch.

(A) Photosynthesis is generally an oxygenic process in plants,algae,and cyanobacteria,where $H_2O$ is used as an electron donor,resulting in the release of $O_2$. However,in certain photosynthetic bacteria like purple and green sulfur bacteria (e.g.,$Rhodospirillum$),$H_2O$ is not used as an electron donor. Instead,they use compounds like $H_2S$ or other organic compounds. Consequently,these organisms do not evolve $O_2$ during photosynthesis. $Spirogyra$,$Chlamydomonas$,and $Ulva$ are algae that perform oxygenic photosynthesis.

(A) Photosynthesis is classified into two types: oxygenic and anoxygenic.
Oxygenic photosynthesis occurs in organisms that use $H_2O$ as an electron donor, releasing $O_2$ as a byproduct. This is characteristic of cyanobacteria (e.g., $Nostoc$), algae (e.g., $Chara$), and higher plants (e.g., $Cycas$).
Anoxygenic photosynthesis occurs in organisms that use other compounds like $H_2S$ as an electron donor instead of $H_2O$. Consequently, they do not produce $O_2$. $Green\,sulphur\,bacteria$ are examples of organisms that perform anoxygenic photosynthesis.
Therefore, the correct answer is $Green\,sulphur\,bacteria$.

(C) Option $C$ is the incorrect statement. The addition of sodium bicarbonate $(NaHCO_3)$ to water provides a source of $CO_2$,which actually enhances the rate of photosynthesis in aquatic plants like $Vallisneria$,rather than retarding it.
$A$ is correct: The $C_4$ pathway was indeed discovered by Hatch and Slack.
$B$ is correct: $CO_2$ is a fundamental substrate required for the Calvin cycle in photosynthesis.
$D$ is correct: Phloem tissue is responsible for the translocation of organic solutes (sugars) from source to sink.

(B) To determine which factor does not differ between $C_3$ and $C_4$ plants,let us analyze each point:
$I.$ Initial $CO_2$ acceptor: In $C_3$ plants,it is $RuBP$,while in $C_4$ plants,it is $PEP$. They differ.
$II.$ Extent of photorespiration: $C_3$ plants show high photorespiration,whereas $C_4$ plants show negligible or no photorespiration. They differ.
$III.$ Enzyme catalyzing $CO_2$ fixation: $C_3$ plants use $RuBisCO$,while $C_4$ plants use $PEP$ carboxylase for initial fixation. They differ.
$IV.$ Presence of Calvin cycle: Both $C_3$ and $C_4$ plants perform the Calvin cycle to synthesize sugars. They do not differ.
$V.$ Leaf anatomy: $C_4$ plants exhibit Kranz anatomy,which is absent in $C_3$ plants. They differ.
Therefore,only $IV$ is common to both.

(A) Statement $(A)$ is correct: The synthesis of $ATP$ from $ADP$ and inorganic phosphate in the presence of light is known as photophosphorylation.
Statement $(B)$ is correct: Kranz anatomy is a specialized structure found in the leaves of $C_4$ plants,where mesophyll cells surround the bundle sheath cells.
Statement $(C)$ is incorrect: During the Calvin cycle (biosynthetic phase),$NADPH$ is oxidized to $NADP^+$ to provide electrons for the reduction of $3-PGA$ to $G3P$. The reduction of $NADP^+$ to $NADPH$ occurs during the light-dependent reactions.
Statement $(D)$ is incorrect: In a chlorophyll molecule,the magnesium ion $(Mg^{2+})$ is located at the center of the porphyrin ring,not in the phytol tail.
Therefore,statements $(A)$ and $(B)$ are correct.

(A) In purple bacteria,photosynthesis utilizes infrared light with wavelengths longer than $700\, nm$ (typically around $800-900\, nm$).
These bacteria contain bacteriochlorophyll as the primary pigment.
The reaction centre in these purple bacteria is known as $B-890$,which absorbs light at this specific wavelength.
Therefore,both the Assertion and the Reason are correct,and the Reason correctly explains why these bacteria can utilize wavelengths longer than $700\, nm$.

(A) $C_4$ plants are more efficient than $C_3$ plants because they have evolved a mechanism to minimize photorespiration.
In $C_4$ plants,the initial $CO_2$ fixation occurs in mesophyll cells via the enzyme $PEP$ carboxylase,which has a high affinity for $CO_2$ and does not bind with $O_2$.
The $CO_2$ is then transported to bundle sheath cells,where it is released at a high concentration,ensuring that the enzyme $RuBisCO$ functions primarily as a carboxylase rather than an oxygenase.
This spatial separation effectively suppresses photorespiration,making the $C_4$ pathway more efficient in terms of carbon fixation and energy utilization compared to the $C_3$ pathway.
Therefore,both the Assertion and the Reason are correct,and the Reason is the correct explanation of the Assertion.

(D) $C_4$ plants are actually more efficient than $C_3$ plants in terms of photosynthesis,especially under conditions of high temperature,high light intensity,and limited water availability,because they lack photorespiration.
Therefore,the Assertion is incorrect.
The $C_4$ pathway involves both mesophyll cells and bundle-sheath cells,which work in coordination to concentrate $CO_2$ around the enzyme $RuBisCO$.
Therefore,the Reason is also incorrect.
Since both the Assertion and the Reason are incorrect,the correct option is $D$.

(D) Dark reaction is also known as light-independent phase. Unlike light reaction,it does not require light as an essential factor. Thus,it can take place both in the presence or absence of light.
The term 'dark reaction' does not mean that it takes place only in the dark period or at night.
$CO_2$ fixation occurs in both $C_3$ and $C_4$ cycles.
In the $C_3$ cycle,$CO_2$ is fixed by the enzyme RuBisCO to a $5$-carbon compound $RuBP$,which is converted into $2$ molecules of $3$-carbon $PGA$.
In the $C_4$ cycle,the first product of $CO_2$ fixation (which takes place in the mesophyll) is a $4$-carbon compound called oxaloacetic acid $(OAA)$.
Since both the Assertion and the Reason are scientifically incorrect,the correct option is $D$.

(A) The cyclic pathway of photosynthesis is considered the most primitive form,appearing first in some eubacterial species. It is the earliest mechanism for $ATP$ production using light energy.
Non-cyclic photophosphorylation involves the photolysis of water,where water molecules are split into oxygen and hydrogen under the influence of light and chlorophyll. This process is the primary natural source of molecular oxygen in the atmosphere. Therefore,oxygen accumulation began only after the evolution of the non-cyclic pathway. Both statements are correct,and the Reason explains why oxygen accumulation is linked to the evolution of the non-cyclic pathway.

(B) The Assertion is correct because the Calvin cycle requires $6$ molecules of $CO_2$,$12$ molecules of $NADPH + H^+$,and $18$ molecules of $ATP$ to synthesize one molecule of hexose (glucose).
The Reason is also correct because the light-dependent reaction (photophosphorylation) produces $ATP$ and $NADPH + H^+$ (often written as $NADPH_2$) which are then utilized in the dark reaction (Calvin cycle).
However,the Reason does not directly explain why exactly $6$ $CO_2$,$12$ $NADPH$,and $18$ $ATP$ are required; it only states the source of these molecules. Therefore,the Reason is not the correct explanation of the Assertion.

(N/A) $\Rightarrow$ Transpiration serves multiple essential purposes in plants.
$\Rightarrow$ It creates a transpiration pull,which is necessary for the absorption and transport of water and minerals from roots to leaves.
$\Rightarrow$ It provides the water required for the process of photosynthesis.
$\Rightarrow$ It cools the leaf surfaces,often by $10$ to $15$ $^{\circ}C$,through evaporative cooling.
$\Rightarrow$ It maintains the shape and structure of plants by keeping cells turgid.
$\Rightarrow$ Photosynthesis and water availability: An actively photosynthesizing plant has a high demand for water. Since photosynthesis is limited by available water,which can be rapidly depleted by transpiration,there is a constant conflict between the two processes.
$\Rightarrow$ The humidity of rainforests is largely maintained by the continuous cycling of water from the soil to the roots,through the plant,and into the atmosphere.
$\Rightarrow$ The evolution of the $C_{4}$ photosynthetic pathway is a strategic adaptation to maximize $CO_{2}$ fixation while minimizing water loss.
$\Rightarrow$ $C_{4}$ plants are twice as efficient as $C_{3}$ plants in fixing carbon.
$\Rightarrow$ Notably,a $C_{4}$ plant loses only half as much water as a $C_{3}$ plant to fix the same amount of $CO_{2}$.

(N/A) $C_{3}$ and $C_{4}$ pathways

$C_{3}$ pathway	$C_{4}$ pathway
$(1)$ The primary acceptor of $CO_{2}$ is $RuBP$ - a five-carbon compound.	$(1)$ The primary acceptor of $CO_{2}$ is phosphoenol pyruvate - a three-carbon compound.
$(2)$ The first stable product is $3$-phosphoglycerate.	$(2)$ The first stable product is oxaloacetic acid.
$(3)$ It occurs only in the mesophyll cells of the leaves.	$(3)$ It occurs in the mesophyll and bundle sheath cells of the leaves.
$(4)$ It is a slower process of carbon fixation and photorespiratory losses are high.	$(4)$ It is a faster process of carbon fixation and photorespiratory losses are low.

$(b)$ Cyclic and non-cyclic photophosphorylation

Cyclic photophosphorylation	Non-cyclic photophosphorylation
$(1)$ It occurs only in photosystem $I$.	$(1)$ It occurs in photosystems $I$ and $II$.
$(2)$ It involves only the synthesis of $ATP$.	$(2)$ It involves the synthesis of $ATP$ and $NADPH$.
$(3)$ In this process,photolysis of water does not occur. Therefore,oxygen is not produced.	$(3)$ In this process,photolysis of water takes place and oxygen is liberated.
$(4)$ In this process,electrons move in a closed circle.	$(4)$ In this process,electrons do not move in a closed circle.

$(c)$ Anatomy of leaf in $C_{3}$ and $C_{4}$ plants

$C_{3}$ leaves	$C_{4}$ leaves
$(1)$ Bundle-sheath cells are absent or poorly developed.	$(1)$ Bundle-sheath cells are present (Kranz anatomy).
$(2)$ $RuBisCo$ is present in the mesophyll cells.	$(2)$ $RuBisCo$ is present in the bundle sheath cells.
$(3)$ The first stable compound produced is $3$-phosphoglycerate - a three-carbon compound.	$(3)$ The first stable compound produced is oxaloacetic acid - a four-carbon compound.
$(4)$ Photorespiration occurs.	$(4)$ Photorespiration is negligible or absent.

(N/A) $\Rightarrow$ All animals,including human beings,depend on plants for their food. Green plants synthesize the food they need,and all other organisms depend on them for their nutritional requirements.
$\Rightarrow$ Green plants carry out 'photosynthesis',a physico-chemical process by which they use light energy to drive the synthesis of organic compounds.
$\Rightarrow$ Since green plants perform photosynthesis and produce their own food,they are classified as autotrophs,while other organisms are heterotrophs.
$\Rightarrow$ Ultimately,all living forms on Earth depend on sunlight for energy. The conversion of solar energy into chemical energy by plants through photosynthesis is the basis of life on Earth.
$\Rightarrow$ Photosynthesis is essential for two primary reasons:
$(A)$ It is the primary source of all food on Earth.
$(B)$ It is responsible for the release of oxygen into the atmosphere,which is essential for the respiration of all aerobic living beings.

(N/A) The products of the light reaction are $ATP$,$NADPH$,and $O_2$. $O_2$ diffuses out of the chloroplast,while $ATP$ and $NADPH$ are used to drive the synthesis of food.
- This is the biosynthetic phase of photosynthesis. It does not directly depend on light but depends on the products of the light reaction ($ATP$ and $NADPH$),along with $CO_2$ and $H_2O$.
- Research of $C_3$ reaction: Scientists were interested in identifying the first product formed when $CO_2$ is fixed. After World War $II$,the use of radioactive $^{14}C$ by Melvin Calvin in algal photosynthesis studies led to the discovery that the first $CO_2$ fixation product was a $3$-carbon organic acid,$3$-phosphoglyceric acid $(PGA)$. This pathway is known as the Calvin cycle.
- Research of $C_4$ reaction: Further experiments on a wide range of plants led to the discovery of another group of plants where the first stable product was a $4$-carbon organic acid,identified as oxaloacetic acid $(OAA)$.
- Consequently,$CO_2$ assimilation is classified into two types:
$(1)$ $C_3$ pathway: Plants where the first product is a $3$-carbon acid $(PGA)$.
$(2)$ $C_4$ pathway: Plants where the first product is a $4$-carbon acid $(OAA)$.

(A)

Characteristics	$C_3$ Plants	$C_4$ Plants
$(1)$ Cell type for Calvin cycle	Mesophyll	Bundle sheath
$(2)$ Cell type for initial carboxylation	Mesophyll	Mesophyll
$(3)$ Number of cell types fixing $CO_2$	Mesophyll	Mesophyll and Bundle sheath
$(4)$ Primary $CO_2$ acceptor	$RuBP$	$PEP$
$(5)$ Carbon number in primary $CO_2$ acceptor	$5C$	$3C$
$(6)$ Primary $CO_2$ fixation product	$PGA$	$OAA$
$(7)$ Carbon number in primary $CO_2$ fixation product	$3C$	$4C$
$(8)$ Presence of RuBisCo	Yes	Yes
$(9)$ Presence of $PEP$ Case	No	Yes
$(10)$ Cells containing RuBisCo	Mesophyll	Bundle sheath
$(11)$ Photorespiration at low light	Negligible	Absent
$(12)$ Photorespiration at high light	Present	Absent
$(13)$ Temperature optimum	$20^{\circ}C - 25^{\circ}C$	$30^{\circ}C - 45^{\circ}C$
$(14)$ Examples	Wheat,Rice	Maize,Sorghum,Sugarcane

(A) $(i)$ The light reactions of photosynthesis take place in the thylakoid membrane of the chloroplast,where chlorophyll pigments are located.
(ii) Ribosomes are non-membrane-bound organelles found in both prokaryotic and eukaryotic cells,whereas lysosomes are single-membrane-bound organelles.

(A) $(1)$ Iron $(Fe)$: Cytochrome is a protein that contains iron as a central metal ion,which is essential for electron transport in respiration and photosynthesis.
$(2)$ Photolysis of water: Manganese $(Mn^{2+})$ is a critical micronutrient required for the photolysis of water during the light-dependent reactions of photosynthesis.

(A) The two primary pathways or circuits for the fixation (installation) of $CO_2$ in plants are the $C_3$ cycle (Calvin cycle) and the $C_4$ cycle (Hatch-Slack pathway).
In the $C_3$ cycle,$CO_2$ is fixed by the enzyme $RuBisCO$ to form a $3$-carbon compound ($3$-$PGA$).
In the $C_4$ cycle,$CO_2$ is initially fixed by the enzyme $PEP$ carboxylase to form a $4$-carbon compound $(OAA)$.
Therefore,the correct answer is $C_3$ and $C_4$ cycles.

(N/A) $(1)$ Differences between Grana and Stroma:

Grana	Stroma
$(1)$ It is the membranous system of the chloroplast.	$(1)$ It is the fluid-filled matrix of the chloroplast.
$(2)$ It contains pigments like chlorophyll $a$,chlorophyll $b$,carotenoids,and xanthophylls.	$(2)$ It contains enzymes required for the biosynthesis of sugars.
$(3)$ Light-dependent reactions take place here.	$(3)$ Light-independent (dark) reactions take place here.
$(4)$ $ATP$ and $NADPH$ are synthesized here.	$(4)$ $ATP$ and $NADPH$ are consumed here to fix $CO_2$.

$(2)$ Differences between $PS-I$ and $PS-II$:

$PS-I$	$PS-II$
$(1)$ The reaction center is $P_{700}$.	$(1)$ The reaction center is $P_{680}$.
$(2)$ It absorbs light at wavelengths up to $700 \; nm$.	$(2)$ It absorbs light at wavelengths up to $680 \; nm$.
$(3)$ It is involved in both cyclic and non-cyclic photophosphorylation.	$(3)$ It is involved only in non-cyclic photophosphorylation.
$(4)$ Electrons released do not necessarily return to the reaction center in non-cyclic flow.	$(4)$ Electrons released are replaced by electrons from water photolysis.
$(5)$ Photolysis of water does not occur.	$(5)$ Photolysis of water occurs.

(N/A) $(1)$ Differences between Light reaction and Dark reaction:

Light reaction	Dark reaction
$(1)$ Occurs in the grana of the chloroplast.	$(1)$ Occurs in the stroma of the chloroplast.
$(2)$ Light is essential for this phase.	$(2)$ Light is not directly required for this phase.
$(3)$ $O_2$ is released due to the photolysis of water.	$(3)$ $CO_2$ fixation occurs in this phase.
$(4)$ It is the first phase of photosynthesis.	$(4)$ It is the second phase of photosynthesis.
$(5)$ $NADPH$ and $ATP$ are produced.	$(5)$ $NADPH$ and $ATP$ are consumed for the reduction of $PGA$.

$(2)$ Differences between Mesophyll cells and Bundle sheath cells:

Mesophyll cells	Bundle sheath cells
$(1)$ Present in both monocot and dicot leaves.	$(1)$ Present in $C_4$ plants,surrounding the vascular bundles.
$(2)$ Chloroplasts contain well-developed grana.	$(2)$ Chloroplasts are often agranal (lack grana).
$(3)$ Primary $CO_2$ fixation occurs here in $C_4$ plants.	$(3)$ Calvin cycle ($C_3$ cycle) occurs here.
$(4)$ Not typically arranged in a ring around vascular bundles.	$(4)$ Arranged in a ring (Kranz anatomy) around vascular bundles.