Mix Examples- Photosynthesis in Higher Plants Questions in English

(N/A) $(1)$ All animals depend directly or indirectly on green plants for their nutrition. Green plants produce food through photosynthesis,which herbivores consume to sustain their lives. Furthermore,the oxygen released during this process is essential for the respiration of all aerobic living organisms.
$(2)$ The process of photosynthesis occurs within the chloroplasts. The light-dependent reaction takes place in the grana,where $ATP$ and $NADPH$ are synthesized. These substances are subsequently utilized in the fixation of $CO_{2}$ during the light-independent reaction (Calvin cycle) to produce glucose. Thus,photosynthesis is a complex anabolic metabolic process.

(N/A) $(1)$ In the $C_4$ pathway,the concentration of $CO_2$ in the chloroplasts of bundle sheath cells remains high. Since the biosynthetic process of carbon fixation occurs in these cells,more $CO_2$ is available,leading to higher carbohydrate production.
Furthermore,the Kranz anatomy prevents $O_2$ produced in the light reaction of mesophyll cells from reaching the bundle sheath cells. Consequently,there is no possibility of photorespiration. Thus,the productivity of the $C_4$ pathway is higher than that of the $C_3$ pathway.
$(2)$ $ATP$ and $NADPH$ produced during the light reaction are utilized in the biosynthetic phase. $CO_2$ combines with the molecule $RuBP$ to form $PGA$. If this cycle runs six times,$6$ molecules of $RuBP$ combine with $6$ molecules of $CO_2$ to form $12$ molecules of $PGAL$. During reduction,two molecules of $PGAL$ are used to synthesize one molecule of glucose,while the remaining $10$ molecules of $PGAL$ regenerate $6$ molecules of $RuBP$. Thus,the cycle continues,allowing for the fixation of atmospheric $CO_2$ and the synthesis of glucose.

(N/A) $(1)$ The dark reaction,also known as the biosynthetic phase of photosynthesis,is the process that utilizes the products of the light reaction ($ATP$ and $NADPH$) to fix $CO_2$ into carbohydrates. It does not directly require light,but it is dependent on the products of the light-dependent reactions.
$(2)$ Photophosphorylation is the process in which $ADP$ combines with inorganic phosphate $(Pi)$ to form $ATP$ using the energy derived from light (photons) during the light-dependent reactions of photosynthesis.

(N/A) $(1)$ Location: Small coin-like structures stacked to form grana.
Function: Site of light-dependent reactions where chlorophyll pigments capture light energy to produce $ATP$ and $NADPH$.
$(2)$ Location: The fluid-filled matrix of the chloroplast surrounding the thylakoids.
Function: Site of the biosynthetic phase (Calvin cycle) where $CO_2$ is fixed to form glucose.

(N/A) $(1)$ $NADP$ stands for Nicotinamide Adenine Dinucleotide Phosphate.
$(2)$ $ATP$ stands for Adenosine Triphosphate.

(N/A) $(1)$ $PGA$ stands for Phosphoglyceric acid, which is the first stable product of the $C_3$ cycle (Calvin cycle) in photosynthesis.
$(2)$ $OAA$ stands for Oxaloacetic acid, which is the first stable product of the $C_4$ cycle (Hatch-Slack pathway) in photosynthesis.

(B) Green plants cannot perform photosynthesis in complete darkness because light energy is essential for the light-dependent reactions of photosynthesis.
Photosynthesis requires light to convert $CO_2$ and $H_2O$ into glucose and oxygen.
To maintain its survival in the dark,the plant can be provided with organic nutrients (like glucose or sucrose) through the soil or by external application,as it cannot synthesize its own food.
However,it will eventually die if kept in the dark for a prolonged period due to the lack of light-dependent metabolic processes.

(A-D) - $RuBP$ Carboxylase: It is involved in the dark reaction (Calvin cycle) for the fixation of $CO_2$ in the $C_3$ pathway.
- $PEPcase$: It is involved in the fixation of $CO_2$ in photosynthesis,specifically in the $C_4$ pathway,where it forms $4C$ oxaloacetate.
- Pyruvate dehydrogenase: It is involved in aerobic respiration,catalyzing the conversion of pyruvic acid into Acetyl $CoA$.
- $ATPase$: It is involved in both respiration and photosynthesis. In both processes,it is associated with the proton pump in the electron transport system,where it synthesizes $ATP$ using the proton gradient.
- Cytochrome oxidase: It is involved in both respiration and photosynthesis as an electron carrier substance in the electron transport chain.
- Hexokinase: It is involved in glycolysis (respiration),where it converts glucose to glucose-$6$-phosphate,consuming one $ATP$.
- Lactate dehydrogenase: It is involved in anaerobic respiration (e.g.,in Lactobacillus),converting pyruvic acid to lactic acid.

(A) $Euphorbia$ is a $CAM$ (Crassulacean Acid Metabolism) plant.
$CAM$ plants are specifically adapted to hot and arid environments because they perform $CO_{2}$ fixation at night when the temperature is lower,which minimizes water loss through transpiration.
$Maize$ is a $C_{4}$ plant,which is also adapted to high temperatures,but $Euphorbia$ (often exhibiting $CAM$ or $C_{4}$ pathways depending on the species) is highly specialized for extreme tropical heat and water stress.
Therefore,$Euphorbia$ is better adapted to survive in harsh tropical conditions.

(N/A) No,it is not correct to say that photosynthesis occurs only in the leaves. While leaves are the primary sites,other green parts of the plant can also perform photosynthesis.
$1$. Photosynthesis by roots: When roots possess chloroplasts and perform photosynthesis,they are called assimilatory roots. Example: $Tinospora$.
$2$. Photosynthesis by stems: In plants like $Opuntia$ (cactus),the stem is modified to act like a leaf. It is green-colored,flat,thick,and fleshy,and it performs photosynthesis. This structure is called a phylloclade.
$3$. Photosynthesis by petioles: In some plants like Australian Acacia,the leaflets fall off very quickly,and the petiole becomes green,flat,and leaf-like to perform photosynthesis. This modified petiole is called a phyllode (often referred to as a cladode in specific contexts).
$4$. Other structures: In plants like $Ruscus$,the stem branches are modified into leaf-like structures called cladodes,which perform photosynthesis.

(N/A) In $C_3$ plants, the enzyme $RuBisCO$ (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is present. It catalyzes the carboxylation of $5C$ $RuBP$ to form $3$-phosphoglycerate $(PGA)$, which is the first stable product of the $C_3$ pathway.
$5C \text{ } RuBP + CO_2 \xrightarrow{RuBisCO} 2 \text{ } PGA$
In $C_4$ plants, the enzyme $PEP$ carboxylase $(PEPCase)$ is present. It catalyzes the carboxylation of phosphoenolpyruvate $(PEP)$ to form oxaloacetic acid $(OAA)$, a $4C$ compound, which is the first stable product of the $C_4$ pathway.
$PEP + CO_2 \xrightarrow{PEPCase} OAA$

(A) $(1)$ The biosynthetic phase (dark reaction) involves the assimilation of $CO_2$ and $H_2O$ to form carbohydrates. Similarly,phosphorylation (specifically photophosphorylation) involves the synthesis of $ATP$ from $ADP$ and inorganic phosphate using light energy.
$(2)$ In the $C_3$ cycle,the first stable product formed after $CO_2$ fixation is $3$-phosphoglyceric acid $(PGA)$. In the $C_4$ cycle,the first stable product formed after $CO_2$ fixation is oxaloacetic acid $(OAA)$.

(A) $(1)$ $C_3$ plants respond to higher $CO_2$ concentrations and show saturation only beyond $450 \,\mu l L^{-1}$.
$(2)$ In photosynthesis,green plants use $H_2O$ as a hydrogen donor,whereas green sulfur bacteria use $H_2S$ (hydrogen sulfide) as a hydrogen donor.

(D) $(1)$ Julius von Sachs provided evidence for the production of glucose when plants grow. He demonstrated that glucose is usually stored as starch.
$(2)$ In $PS-II$ (Photosystem-$II$),the reaction center chlorophyll-$a$ has an absorption peak at $680 \, nm$. Therefore,it is also called $P680$.
$(3)$ Since both statements contain incorrect pairings or values in the original prompt,we identify the correct scientific facts: Julius von Sachs is the correct scientist for the glucose/starch experiment,and $680 \, nm$ is the correct wavelength for $PS-II$.

(A) $(1)$ In the $C_3$ cycle (Calvin cycle),the first stable product formed after the carboxylation of $RuBP$ is a $3$-carbon compound called $3$-phosphoglyceric acid $(PGA)$.
$(2)$ In the $C_4$ pathway (Hatch-Slack pathway),the primary $CO_2$ acceptor is phosphoenolpyruvate $(PEP)$,which is a $3$-carbon compound,and it combines with $CO_2$ to form oxaloacetic acid $(OAA)$.

(A) $(1)$ Maize ($Zea$ $mays$) is a $C_4$ plant,whereas Sunflower is a $C_3$ plant.
$(2)$ Rubisco ($Ribulose$ $1,5-bisphosphate$ $carboxylase-oxygenase$) is the most abundant enzyme in the world because it is essential for the Calvin cycle in all photosynthetic plants.

(A) $(1)$ $C_4$ plants are more efficient in carbon fixation than $C_3$ plants because they possess the $\text{Kranz}$ anatomy and the $\text{PEP}$ carboxylase enzyme, which minimizes photorespiration.
$(2)$ The translocation of sugars (sucrose) from the source (leaves) to the sink (roots, fruits, or storage organs) occurs through the $\text{phloem}$ tissue, as described by the pressure-flow hypothesis.

(C) Photosynthetic bacteria,such as purple and green sulphur bacteria,perform photosynthesis in anoxic (oxygen-free) environments.
These organisms use bacteriochlorophyll instead of chlorophyll $a$.
Instead of water $(H_{2}O)$,they use other hydrogen donors like hydrogen sulphide $(H_{2}S)$ or organic compounds.
Because water is not split during this process,oxygen is not evolved as a byproduct.

(D) Passive absorption of water by the root system occurs due to the tension created in the xylem water column,which is a result of transpiration.
Absorption of ions from the soil occurs through both active and passive transport mechanisms.
The $C_{4}$ photosynthetic system is an adaptation found in many tropical plants (e.g.,maize,sugarcane,sorghum,Amaranthus) to maximize $CO_{2}$ availability and minimize water loss through photorespiration.
Therefore,all the given statements are correct.

(D) Diffusion is a passive process where molecules move from a region of higher concentration to a region of lower concentration along the concentration gradient.
It plays a crucial role in various biological processes:
$1$. In $Transpiration$, water vapor diffuses out of the stomata into the atmosphere.
$2$. In $Respiration$, oxygen diffuses into cells and carbon dioxide diffuses out.
$3$. In $Photosynthesis$, carbon dioxide diffuses into the leaves from the atmosphere, and oxygen diffuses out.
Therefore, it is involved in all of these processes.

(A) $I.$ True: $CAM$ plants open stomata at night to minimize water loss.
$II.$ False: The role of $Na^+$ in stomatal opening is not universally accepted; $K^+$ is the primary ion involved.
$III.$ False: For water absorption,the water potential of root cells must be lower than that of the soil.
$IV.$ False: The Cohesion-Tension (Transpiration Pull) theory is the most widely accepted theory for water transport.
$V.$ True: Xylem walls are hydrophilic due to ligno-cellulose,facilitating water movement.
Therefore,statements $II, III,$ and $IV$ are not true.

(B) In $C_{3}$-plants,the entire Calvin cycle occurs within the mesophyll cells.
In $C_{4}$-plants,the Calvin cycle is restricted to the bundle sheath cells,while the initial carbon fixation occurs in the mesophyll cells.
Therefore,statement $I$ is correct,and statement $II$ is incorrect.

(C) Loss of all leaves would do maximum harm to a tree.
Leaves are the primary sites for photosynthesis,which is the process by which plants produce their food.
Without leaves,the plant cannot synthesize glucose,leading to a complete cessation of energy production.
This results in the starvation of the plant and the eventual cessation of all metabolic activities,leading to the death of the tree.

(D) Photosynthesis is the process by which green plants synthesize their own food using specific components.
According to the chemical equation for photosynthesis: $6CO_{2} + 6H_{2}O \xrightarrow{\text{Light, Chlorophyll}} C_{6}H_{12}O_{6} + 6O_{2}$.
From this equation,it is evident that $H_{2}O$ (water) and $CO_{2}$ (carbon dioxide) are the chemical raw materials,while light and chlorophyll are essential requirements for the process to occur.
Therefore,all the listed items $(I, II, III, IV)$ are necessary for photosynthesis.

(C) The two pigment system theory of photosynthesis,which describes the existence of $PS-I$ and $PS-II$,was proposed by $Emerson$ et al. based on the observation of the enhancement effect in photosynthesis.

(A) RuBisCo is the most abundant protein in the biological world.
It constitutes approximately $16 \%$ of the total chloroplast proteins.
It is an enzyme that plays a crucial role in the Calvin cycle during photosynthesis.
It is located on the outer surface of the thylakoid membrane.

(B) All life forms are supported by plants, whether they are herbivores or carnivores. Chloroplasts present in plants trap solar energy and convert it into chemical energy in the form of starch. This process is known as photosynthesis. Therefore, the statement "We are created by chloroplast" implies that all life forms depend on photosynthesis for their survival and energy requirements.

(D) $C_{4}$-plants exhibit Kranz anatomy. In these plants,the primary carbon dioxide acceptor in mesophyll cells is phosphoenol pyruvate $(PEP)$.
In the light reaction of photosynthesis,$PS-II$ absorbs energy at or just below $680 \;nm$,which is why its reaction center is called $P680$.
$PS-I$ absorbs energy at $700 \;nm$,and its reaction center is called $P700$.
Therefore,statements $I$ and $II$ are correct,while statement $III$ is incorrect because $P680$ is the reaction center of $PS-II$,not $PS-I$.

(B) $CO_{2}$ assimilation during photosynthesis generally takes place in two ways in plants:
$(i)$ $C_{3}$ pathway: Those plants in which the first stable product of $CO_{2}$ fixation is a $C_{3}$ acid,specifically $3$-phosphoglyceric acid $(PGA)$,are said to follow the $C_{3}$ pathway.
$(ii)$ $C_{4}$ pathway: Those plants in which the first stable product of $CO_{2}$ fixation is a $C_{4}$ acid,specifically oxaloacetic acid $(OAA)$,are said to follow the $C_{4}$ pathway.

(C) Photosynthesis is an anabolic process of manufacturing organic compounds.
It is characterized by the reduction of $CO_2$ to carbohydrates and the oxidation of water to $O_2$.
This process decreases the concentration of $CO_2$ in the atmosphere and increases the concentration of $O_2$.

(D) In oxygenic photosynthesis,water $(H_2O)$ acts as an electron donor,and oxygen $(O_2)$ is released as a byproduct. This occurs in plants,algae,and cyanobacteria (blue-green algae).
In contrast,photosynthetic bacteria (such as purple and green sulphur bacteria) perform anoxygenic photosynthesis.
In these bacteria,compounds like hydrogen sulphide $(H_2S)$ or other inorganic substances act as electron donors instead of water.
Consequently,these bacteria do not evolve oxygen during the process of photosynthesis.

(B) The Calvin cycle is present in both $C_{3}$ and $C_{4}$ plants.
In $C_{3}$ plants,the Calvin cycle occurs in the mesophyll cells.
In $C_{4}$ plants,the Calvin cycle occurs in the bundle sheath cells.
Since the Calvin cycle is a fundamental process for carbon fixation in both types of plants,its presence does not differ between them.
Other factors like the initial $CO_{2}$ acceptor (RuBP in $C_{3}$,$PEP$ in $C_{4}$),extent of photorespiration (higher in $C_{3}$,negligible in $C_{4}$),enzymes (RuBisCO in $C_{3}$,$PEP$ carboxylase and RuBisCO in $C_{4}$),and leaf anatomy (Kranz anatomy in $C_{4}$) differ significantly.

(C) The statement in option $C$ is false because carbon dioxide fixation (Calvin cycle) occurs in the stroma of the chloroplast,not in the grana. The stroma contains the necessary enzymes,such as $RuBisCO$,which are essential for the fixation of carbon dioxide and the subsequent synthesis of sugars. The grana are primarily the sites for the light-dependent reactions.

(D) Photosynthesis is an endergonic process because it requires the input of energy (light energy) to synthesize organic compounds.
It is a chemical process as it involves the conversion of inorganic raw materials ($CO_2$ and $H_2O$) into organic compounds (glucose) through a series of chemical reactions.
It is not an exergonic process (which releases energy) nor is it a purely physical process.
Therefore,statements $I$ and $III$ are correct.

(C) Water $(H_2O)$ plays a crucial role in photosynthesis.
$1$. In the light reaction,water undergoes photolysis (splitting of water) to provide electrons,protons $(H^+)$,and oxygen $(O_2)$. Thus,it acts as a reactant.
$2$. Water is also involved in the dark reaction (Calvin cycle) as it is required for various metabolic processes and is a product of the condensation reactions occurring during sugar synthesis.
Therefore,water is involved in both light and dark reactions.

(D) High $CO_{2}$ concentration promotes the carboxylation reaction of $RuBisCO$,thereby increasing the rate of the Calvin cycle to synthesize carbohydrates.
High $ATP/ADP$ ratio indicates an energy-rich state,which further supports the Calvin cycle.
These conditions inhibit photorespiration (glycolate cycle) because $RuBisCO$ acts as a carboxylase rather than an oxygenase.
Additionally,metabolic regulation often leads to a decrease in the rate of the Kreb cycle under these conditions to balance cellular energy requirements.

(D) $PS-I$ (Photosystem-$I$) is a photosynthetic pigment system along with some electron carriers that is located on both the non-appressed parts of grana thylakoids as well as stroma thylakoids.
$PS-II$ (Photosystem-$II$) is a photosynthetic pigment system along with some electron carriers that is located in the appressed part of grana thylakoids.
Therefore,both statements $I$ and $II$ are incorrect.

(B) Statement $I$ is false because Photosynthetically Active Radiation $(PAR)$ ranges between $400-700 \;nm$,not $300-500 \;nm$.
Statement $II$ is false because manganese $(Mn^{2+})$ and chloride $(Cl^-)$ ions are essential for the photolysis of water,not magnesium or calcium.
Statement $III$ is true because cyclic photophosphorylation involves only Photosystem $I$ $(PSI)$,where water is not split (no photolysis),thus no oxygen is released and no $NADPH$ is formed.

(B) Photosynthesis is a physico-chemical process by which green plants use light energy to drive the synthesis of organic compounds.
It is an anabolic and reductive process.
It occurs in both unicellular and multicellular photoautotrophs.
However,oxygen is not evolved as a by-product in all photosynthetic organisms. For example,in purple and green sulfur bacteria,$H_2S$ is used as a hydrogen donor instead of $H_2O$,and therefore,sulfur or sulfate is produced instead of $O_2$.

(B) In $C_3$ plants,the primary $CO_2$ acceptor is $RuBP$ (Ribulose$-1,5-$bisphosphate),which is a $5$-carbon compound.
In $C_4$ plants,the primary $CO_2$ acceptor is $PEP$ (Phosphoenolpyruvate),which is a $3$-carbon compound.
Therefore,$C_4$ and $C_3$ plants differ significantly in their primary $CO_2$ acceptor during the carbon fixation process.

(D) In $C_4$ plants,the primary carbon fixation occurs in mesophyll cells and is catalysed by $PEP$ carboxylase.
Additionally,mesophyll cells lack the $RuBisCO$ enzyme,which is instead restricted to the bundle sheath cells.
Furthermore,$C_4$ plants have a mechanism that increases the concentration of $CO_2$ around the $RuBisCO$ enzyme,which effectively minimizes or eliminates photorespiration.
Since all three statements ($A$,$B$,and $C$) are correct,the correct option is $D$.

(A) The correct matches are as follows:
$1$. $OEC$ (Oxygen Evolving Complex) is responsible for the photolysis of $H_2O$ $(a-ii)$.
$2$. $NADP$ reductase enzyme is located on the outer surface of the thylakoid membrane, where it reduces $NADP^+$ to $NADPH$ $(b-iii)$.
$3$. Succinyl $CoA$ is a precursor molecule involved in the biosynthesis of chlorophyll $(c-iv)$.
$4$. Phaeophytin acts as the primary electron acceptor in the electron transport chain of Photosystem-$II$ $(d-i)$.
Therefore, the correct sequence is $a(ii), b(iii), c(iv), d(i)$.

(D) Maize is a $C_4$ plant,while wheat is a $C_3$ plant.
$C_4$ plants like maize require more $ATP$ ($30$ $ATP$ per glucose) compared to $C_3$ plants like wheat ($18$ $ATP$ per glucose) for $CO_2$ fixation.
$C_4$ plants exhibit spatial separation of carboxylations (mesophyll and bundle sheath cells),whereas $C_3$ plants do not.
$C_4$ plants utilize $PEP$case enzyme for the initial $CO_2$ fixation,which is absent in $C_3$ plants.
Therefore,all the given options represent differences between maize and wheat photosynthesis.

(A) The Light Harvesting Complexes $(LHC)$ consist of hundreds of pigment molecules bound to proteins. Each complex contains all pigments except one molecule of chlorophyll $a$,forming a light-harvesting system (also called antenna molecules).
These pigments absorb light at different wavelengths,thereby broadening the range of light absorption for photosynthesis.
The energy absorbed by these antenna molecules is transferred to the reaction centre (chlorophyll $a$) via resonance.
Therefore,both the Assertion and the Reason are correct,and the Reason explains why the $LHC$ is effective in light absorption.

(B) $1$. In the $C_3$ cycle (Calvin cycle),the fixation of one molecule of $CO_2$ requires $3$ $ATP$ and $2$ $NADPH$ molecules.
$2$. The light reaction produces $ATP$ and $NADPH$ in a specific ratio. However,the $C_3$ cycle requires a higher ratio of $ATP$ to $NADPH$ than what is produced by non-cyclic photophosphorylation alone.
$3$. Cyclic photophosphorylation occurs to produce additional $ATP$ to compensate for this deficit.
$4$. While both statements are scientifically accurate,the Reason does not directly explain why the $C_3$ cycle specifically requires $3$ $ATP$ and $2$ $NADPH$; it only explains how the cell manages the $ATP$ demand. Therefore,the Reason is not the correct explanation for the Assertion.

(C) The Assertion is correct because chlorophyll $a$ and $b$ absorb light most efficiently in the blue and red regions of the visible spectrum,leading to higher rates of photosynthesis in these regions.
The Reason is incorrect because an action spectrum depicts the magnitude of a biological response (such as the rate of photosynthesis) as a function of light wavelength. It does not show the amount of energy absorbed by pigments; that is the definition of an absorption spectrum.

(A) In eukaryotes,photosynthesis takes place within specialized organelles known as chloroplasts. These organelles contain chlorophyll pigments that capture light energy. In contrast,prokaryotic organisms,which lack membrane-bound organelles,perform photosynthesis in the cytoplasm or specialized plasma membrane extensions.

(A) $DCMU$ ($3$-($3$,$4$-dichlorophenyl)$-1,1-$dimethylurea) is a herbicide that acts as an inhibitor of non-cyclic electron transport by blocking the plastoquinone binding site.
$PMA$ (Phenylmercuric acetate) is a fungicide that also acts as an anti-transpirant by reducing the rate of transpiration in plants.
Colchicine is an alkaloid that inhibits mitosis by preventing the formation of spindle fibers; it does not cause male sterility.
Soilrite is a commercial mixture of expanded perlite and vermiculite,not sodium alginate. Sodium alginate is used for the encapsulation of somatic embryos in synthetic seed production.

(A) $DCMU$ ($3$-($3$,$4$-dichlorophenyl)$-1,1-$dimethylurea) is a herbicide that acts as an inhibitor of non-cyclic electron transport in photosynthesis.
$PMA$ (Phenylmercuric acetate) is a fungicide that also acts as an anti-transpirant by reducing transpiration.
Colchicine is an alkaloid that inhibits mitosis by preventing the formation of spindle fibers; it does not cause male sterility.
Soilrite is a commercial medium used for the encapsulation of somatic embryos,but it is not composed of sodium alginate (sodium alginate is used for the encapsulation process itself).
Therefore,the correct pairs are $I$ and $II$.

(C) Sugarcane is a $C_4$ plant,while sugar beet is a $C_3$ plant.
These two types of plants follow different photosynthetic pathways,which leads to a difference in the fractionation of stable carbon isotopes.
Specifically,$C_4$ plants like sugarcane incorporate more $C^{13}$ relative to $C^{12}$ compared to $C_3$ plants like sugar beet.
Therefore,the $C^{13} / C^{12}$ ratio is a reliable marker used to distinguish between the sugar derived from these two sources.