Photosynthesis MCQ Quiz in తెలుగు - Objective Question with Answer for Photosynthesis - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Concept:

• The complexes involved in photosynthesis are heterogenously distributed between stacked and unstacked membranes: PS II centers and their peripheral antenna are essentially localized in stacked regions of the membranes, whereas PS I centers, their peripheral antenna and ATP synthase are exclusively located in unstacked areas; the cytochrome b6f complex is distributed in both membrane domains.
• Each of these protein complexes can be visualized by freeze-fracture as individual particles, but they can also be found in association with other proteins: in particular, the peripheral antennae are, in part, associated with their corresponding reaction centers to form large PFu or EFs particles.
• It has also been suggested that some Cyt b6f complexes may be associated within the same particle with PS I or PS II reaction centers.
• Another important characteristic of intramembrane complexes is their lateral mobility.
• Destacking of the membranes by removal of divalent cations induces a random redistribution of the proteins in the membrane.
• State transitions also cause a lateral displacement of the mobile part of the PS II peripheral antenna, and of some Cyt b6f complexes, along the thylakoid membranes

Explanation:

Statement A: PSII is preferentially located on grana lamellae

• The thylakoid layers inside the chloroplast contain the photosystems I and II (PS I and PS II).
• The photochemical step, also known as the light reaction, of photosynthesis is carried out by the photosystems.
• These two photosystems have a slightly distinct relative distribution, with more PSII found in grana lamellae and more PSI found in stroma lamellae.
• thus this statement is  true

Statement B: ATP synthase and PSI are preferentially located on stroma lamellae

• The chloroplast ATP synthase is confined to minimally curved regions at the grana end membranes and stroma lamellae, where it covers 20% of the surface area.
• PSI, LHCI, and ATP synthase are found in the non-stacked stroma lamellae

Statement C: PSI and PSII are located adjacent to each other on stroma lamellae

•   Consider the explanation above thus this option is not true

Statement D: Cytochrome B6/f complex is not membrane bound complex

• The cytochrome b6f complex is closely analogous to complex III in oxidative phosphorylation. It plays a major role in generating a protein gradient during photosynthesis.
• An X-ray crystal structure of cytochrome b6f shows that it is a membrane-bound protein.
• thus this statement is not true

Concept:

• Photorespiration is a process that occurs in plants when the concentration of carbon dioxide in the air is low or when the temperature is high, leading to a reduction in the efficiency of photosynthesis.
• In photorespiration, Rubisco, the enzyme responsible for fixing carbon dioxide in the Calvin cycle, can also react with oxygen instead of carbon dioxide.
• This reaction results in the formation of a two-carbon compound called glycolate, which is further converted into glycine by the action of several enzymes.
• Glycine then enters the photorespiratory pathway, which involves a series of reactions that occur mainly in the mitochondria and peroxisomes of plant cells.
• These reactions result in the release of carbon dioxide and the production of other metabolites that are eventually used by the plant in various metabolic processes.
• The photorespiratory pathway is a complex process that involves several enzymes and metabolic pathways. It is often considered a wasteful process because it results in the loss of energy and organic compounds.
• However, it is also essential for the survival of plants under certain environmental conditions because it prevents the accumulation of toxic compounds and helps in the maintenance of the balance between carbon dioxide and oxygen in the plant cells.

Explanation:

• During photorespiration, Rubisco enzyme can also react with oxygen instead of carbon dioxide, resulting in the formation of a two-carbon compound called glycine.
• This compound then enters the photorespiratory pathway and is eventually converted into CO₂ and other metabolites in a series of reactions that occur mainly in the mitochondria and peroxisomes of plant cells.

 So, option 4, Glycine is the correct answer.  

Key Points

• C3 and C4 plants have different mechanisms for CO2 compensation, which is the ability to maintain an adequate supply of carbon dioxide (CO2) for photosynthesis, especially under conditions of low CO2 or high temperature.

C3 Plants:

• C3 plants, such as rice, wheat, and most trees, utilize the C3 photosynthetic pathway.
• In C3 plants, the first product formed during photosynthesis is a three-carbon compound called 3-phosphoglyceric acid (PGA).
• C3 plants do not have specialized CO2-concentrating mechanisms.
• In C3 plants, CO2 compensation occurs through a process called photorespiration. Photorespiration is a side reaction that competes with photosynthesis for the CO2 and oxygen (O2) molecules. Under certain conditions, such as high temperatures and low CO2 levels, photorespiration becomes more prevalent, reducing the efficiency of photosynthesis.
• To compensate for the loss of CO2 through photorespiration, C3 plants typically increase their overall rate of photosynthesis when there is an ample supply of CO2.
• They also regulate stomatal openings, adjusting the size of leaf openings (stomata) to control the entry of CO2 and minimize water loss through transpiration.

C4 Plants:

• C4 plants, such as maize, sugarcane, and certain grasses, have evolved a specialized C4 photosynthetic pathway.
• In C4 plants, CO2 compensation occurs through spatial separation of initial CO2 fixation and the Calvin cycle, which reduces the negative effects of photorespiration.
• C4 plants have two types of photosynthetic cells: mesophyll cells and bundle sheath cells.
• The mesophyll cells initially fix CO2 into a four-carbon compound called oxaloacetate, which is then converted to malate or aspartate and transported to the bundle sheath cells.
• Within the bundle sheath cells, CO2 is released from malate or aspartate and enters the Calvin cycle, where it is used for carbohydrate synthesis.
• This spatial separation allows C4 plants to maintain higher concentrations of CO2 around the enzyme responsible for initial CO2 fixation, reducing the occurrence of photorespiration.
• C4 plants also exhibit a higher CO₂ affinity in the Calvin cycle, enhancing the efficiency of photosynthesis under low CO₂ conditions.

Explanation:

• The CO2 compensation point is the CO2 level at which respiration and photosynthesis occur at the same rate.
• Between C3 plants and C4 plants, there is a substantial variation in CO2 compensation point on land, the normal value for CO2 compensation point in a C3 plant varies from 40 to 100 mol/mol, while the values are lower in C4 plants at 3 to 10 mol/mol.
• Plants whose CCM is weaker, as those whose photosynthesis is based on C₂, may have an intermediate value at 25 mol/mol.

Hence, the correct answer is option 3.

The correct answer is Option 2 i.e. B and D

Concept:

• Carbon atoms from carbon dioxide are fixed (incorporated into organic molecules) and used to create three-carbon sugars in the Calvin cycle.
• ATP and NADPH (the product of the light reaction) are used to power and support this activity.
• Calvin cycle reactions occur in the stroma, while light reactions occur in the thylakoid membrane (the inner space of chloroplasts).
• Calvin's cycle consists of three stages as follows:

1. Carbon fixation - 
   • In the first step, carbon dioxide enters the Calvin cycle.
   • \(CO_2\)  is added to the carbon 2 of Ribulose-1,5-bisphosphate, a five-carbon acceptor molecule, to form an enzyme-bound intermediate that is further hydrolyzed to yield two molecules of stable 3-phosphoglycerate (3-PGA).
   • The RuBP carboxylase/oxygenase enzyme, which is known as rubisco, catalyzes the reaction.
2. Reduction -
   • 3-PGA undergoes two modifications under the reduction stage of the Calvin cycle.
   • 3-PGA phosphorylate by enzyme 3-phosphoglycerate kinase to form 1,3-biphosphoglycerate. ATP molecule generated in the light reaction is utilised in this reaction.
   • In the second modification, 1,3-bisphosphoglycerate is reduced by NADP:glyceraldehyde-3-phosphate dehydrogenase to form glyceraldehyde-3-phosphate (G3P).
   • NADPH molecule generated in the light reaction is utilized in this reaction.
3. Regeneration-
   • One G3P is used for making glucose while the other is used for the regeneration of RuBP.
   • For the formation of a glucose molecule, plants have to perform six rounds of the Calvin cycle.

Explanation:

Statement A: INCORRECT

• ATP and NADPH formed in the light reaction are used in the reduction stage of the Calvin cycle.

Statement B: CORRECT

• 3-phosphoglycerate is converted to glyceraldehyde-3-phosphate in the reduction phase of the Calvin cycle.
• For the formation of one glucose molecule, six molecules of 3-phosphoglycerate are converted into six molecules of glyceraldehyde 3-phosphate in the reduction phase.

Statement C: INCORRECT

• The action of the aldolase enzyme for the production of fructose 1, 6-bisphosphate takes place in the regeneration phase of the Calvin cycle.

Statement D: CORRECT

• The formation of seven carbon compounds, sedoheptulose-7- phosphate takes place in the regeneration phase of the Calvin cycle.

Hence, the correct answer is Option 2.

The correct answer is Option 2 i.e. A and C

Concept:

• RuBisCo is an important enzyme in the plant kingdom with the ability to catalyse both carboxylation and oxygenation of ribulose-1,5-bisphosphate (RuBP).
• In the process of photorespiration, oxygenation is the primary reaction.
• The photorespiration cycle involves the cooperation of three organelles - mitochondria, peroxisomes, and chloroplast.
• In chloroplast, ribulose-1,5-bisphosphate react with oxygen to form 2-phosphoglycolate, RuBisCo enzyme catalyses this oxygenation reaction.
• After forming, 2-phosphoglycolate is rapidly hydrolysed to form glycolate.
• Glycolate leaves chloroplast and diffuses to the peroxisomes, where it is oxidized to form glyoxylate and hydrogen peroxide. This reaction is catalysed by flavin mononucleotide-dependent oxidase: glycolate oxidase. 
• Glyoxylate undergoes transamination to form glycine. 
• glycine leaves the peroxisomes to enter the mitochondria where glycine decarboxylase catalyses the conversion of two molecules of glycine to form serine. 
• Serine is transported to the peroxisome and transformed into glycerate.
• glycerate leaves peroxisomes and enters chloroplast where it is phosphorylated to form 3-phosphoglycerate and incorporated into the Calvin cycle.

Explanation:

• In chloroplast, RuBisCo reacts with oxygen to form 2-phosphoglycolate and one molecule of 3PGA. 
• 2-phosphoglycolate is the first 2-C compound that is synthesised in the chloroplast by the action of RuBisCo enzyme.
• 2-phosphoglycolate is then converted to glycolate.
• So, statement 'A' is incorrect.
• Glycolate forms in the chloroplast leave the chloroplast and enter the peroxisome. 
• So, statement 'B' is correct and statement 'C' is incorrect.
• In the peroxisome, 2glycolate is first converted to glyoxylate and later to glycine. 
• Glycine leaves the peroxisome and enters mitochondria.
• So, statement 'D' is correct.

Hence, the correct answer is option 2.

The correct answer is Option 1 and Option 2

Explanation:

• The enzyme aldolase (specifically Fructose-1,6-bisphosphate aldolase, but also other aldolases) catalyzes aldol condensation or retro-aldol cleavage reactions.
• Its primary role in glycolysis is the reversible cleavage of fructose 1,6-bisphosphate.
• However, aldolases are also involved in other metabolic pathways, such as the Calvin cycle and the pentose phosphate pathway, where they catalyze similar reactions involving different sugar phosphates.

Dihydroxyacetone phosphate + Glyceraldehyde-3-phosphate → Fructose 1,6-biphosphate:

• This is the synthesis of fructose 1,6-bisphosphate from two triose phosphates. This is the reverse reaction of a key step in glycolysis and is directly catalyzed by aldolase.
• (3-carbon DHAP + 3-carbon G3P → 6-carbon FBP)

Dihydroxyacetone phosphate + Erythrose-4-phosphate → Sedoheptulose-1,7-biphosphate:

• This reaction occurs in the Calvin cycle (in plants) and also in the non-oxidative phase of the pentose phosphate pathway.
• An aldolase catalyzes the condensation of the 3-carbon dihydroxyacetone phosphate with the 4-carbon erythrose-4-phosphate to form the 7-carbon sedoheptulose-1,7-bisphosphate. This reaction is indeed catalyzed by aldolase.
• (3-carbon DHAP + 4-carbon E4P → 7-carbon SBP)

(GAP = glyceraldehyde 3-phosphate, PRPP = 5-O-phosphono- ribose 1-diphosphate, R5P = ribose 5-phosphate, Ru5P = ribulose 5-phosphate, RuBP = ribulose 1,5-bisphosphate, S7P = sedoheptulose 7-phosphate, SBP = sedoheptulose 1,7-bisphosphate, SBPase = sedoheptulose 1,7-bisphosphatase, and Xu5P = xylulose 5-phosphate)

The correct answer is Option 1 and Option 4

Explanation:

Malic enzymes (ME) are a family of enzymes found in plants that catalyze the oxidative decarboxylation of L-malate, producing pyruvate, CO₂, and NAD(P)H. Their classification depends on the coenzyme they use.

1. Malate + NAD+ → Pyruvate + CO₂ + NADH

• This reaction is catalyzed by NAD-dependent malic enzyme (NAD-ME) (EC 1.1.1.38 and EC 1.1.1.39).
• In plants, NAD-ME is primarily found in the mitochondria and plays a role in various metabolic processes, including the C4 photosynthetic process in some species and general housekeeping functions by channeling malate to the TCA cycle.

4. Malate + NADP+ → Pyruvate + CO₂ + NADPH

• This reaction is catalyzed by NADP-dependent malic enzyme (NADP-ME) (EC 1.1.1.40).
• In plants, NADP-ME is found in the chloroplasts and cytosol.
• It is crucial for providing NADPH for various anabolic reactions, including fatty acid synthesis, and plays a significant role in C4 photosynthesis and plant defense responses

Other Options:

2. Malate + NAD+ ⇌ Oxaloacetate + NADH

• This reaction is catalyzed by Malate Dehydrogenase (MDH) (EC 1.1.1.37). MDH is involved in the reversible interconversion of malate and oxaloacetate in the TCA cycle and malate-aspartate shuttle.

3. Malate ⇌ Fumarate

• This reaction is catalyzed by Fumarase (also known as fumarate hydratase, EC 4.2.1.2), an enzyme in the TCA cycle that interconverts fumarate and malate.

The correct answer is Pheophytin - Plastoquinone A - Plastoquinone B - Cytochrome b₆f complex - Plastocyanin

Concept:

• The light-dependent reactions of photosynthesis occur in the thylakoid membranes of chloroplasts in plants. These reactions involve two photosystems: Photosystem II (P680) and Photosystem I (P700).
• The electron transport chain (ETC) facilitates the transfer of electrons from P680 in Photosystem II to P700 in Photosystem I, producing ATP and NADPH in the process.
  • Pheophytin: The primary electron acceptor in Photosystem II (P680). It receives excited electrons from chlorophyll molecules in P680.
  • Plastoquinone A: Pheophytin transfers electrons to Plastoquinone A, a mobile electron carrier within the thylakoid membrane.
  • Plastoquinone B: Electrons are transferred from Plastoquinone A to Plastoquinone B. These molecules shuttle electrons to the next complex in the chain.
  • Cytochrome b6f Complex: This protein complex accepts electrons from Plastoquinone B and uses the energy to pump protons (H⁺) into the thylakoid lumen, contributing to the proton gradient needed for ATP synthesis.
  • Plastocyanin: A mobile copper-containing protein that transfers electrons from the Cytochrome b6f Complex to Photosystem I (P700), completing the chain.

The correct answer is A and D

Concept:

• RuBisCO (Ribulose-1,5-bisphosphate carboxylase-oxygenase) is a critical enzyme in the Calvin cycle, which occurs in the chloroplasts of photosynthetic organisms. It catalyzes two competing reactions: carboxylation and oxygenation of ribulose-1,5-bisphosphate (RuBP).
• Carboxylation leads to the production of 3-phosphoglycerate (3-PGA), which is used in the synthesis of carbohydrates, while oxygenation generates 3-PGA and 2-phosphoglycolate, a metabolically wasteful product.
• The catalytic mechanism of RuBisCO involves multiple steps, including enolization, carbon-carbon bond cleavage, and the addition of either CO₂ (carboxylation) or O₂ (oxygenation).

Explanation:

Statement A: "The first step of catalysis is enolization of RuBP."

• This is correct. The initial step in the catalytic cycle of RuBisCO involves the enolization of RuBP. During this step, RuBP is converted into an enediol intermediate, which is essential for the subsequent addition of CO₂ or O₂.

Statement B: "The carbon-carbon bond between C3 and C4 of RuBP is cleaved."

• This is incorrect. In both carboxylation and oxygenation reactions catalyzed by RuBisCO, the bond between the C2 and C3 (not C3 and C4) carbon atoms of RuBP is broken during the reaction, resulting in the formation of two smaller molecules.

Statement C: "Carboxylase activity produces only one molecule of 3-phosphoglycerate."

• This is incorrect. The carboxylase activity of RuBisCO produces two molecules of 3-phosphoglycerate (3-PGA) when CO₂ is added to RuBP. 

Statement D: "Oxygenase activity produces one molecule of 3-phosphoglycerate and one molecule of 2-phosphoglycolate."

• This is correct. When RuBisCO acts as an oxygenase, it adds O₂ to RuBP, producing one molecule of 3-phosphoglycerate (3-PGA) and one molecule of 2-phosphoglycolate. The latter is a metabolically wasteful product that requires energy to recycle.

Fig:  RuBP conversion by Rubisco through the carboxylase (a) and the oxygenase (b) reactions.

• Following RuBP (1) enolization, the 2,3-enol(ate) intermediate (2) may react with CO2 (a) or O2 (b) co-substrates. The carboxylase reaction produces the 2-carboxy-3-keto-arabinitol 1,5-bisphosphate intermediate (3) undergoing protonation to the 2-carboxylic acid before hydration. The C2-C3-scission reaction in C3-gemdiolate (5) is described occurring in a concerted mechanism upon P1 protonation through a Grotthuss mechanism, producing two molecules of 3-phospho-D-glycerate (3PGA, 6). The oxygenase reaction produces 3-phospho-D-glycerate (3PGA, 6) and 2-phosphoglycolate (2PG, 7). 

The correct option is: 2

Explanation:

• Chlorophyll absorbs light most efficiently in the blue (around 430–450 nm) and red (around 640–680 nm) regions of the light spectrum. These wavelengths are used in photosynthesis to drive the conversion of light energy into chemical energy.
• Green light (around 500–570 nm) is largely reflected by chlorophyll, which is why plants appear green to the human eye. Chlorophyll absorbs very little green light.
• Yellow (around 570–590 nm) and infrared (700 nm and above) light are not absorbed as efficiently by chlorophyll for photosynthesis. Infrared light has lower energy and does not contribute significantly to the photosynthetic process.
• Chlorophyll's absorption of blue and red light is essential for the light-dependent reactions of photosynthesis. In these reactions, light energy is used to produce ATP and NADPH, which are then used in the light-independent reactions (Calvin cycle) to fix carbon into glucose.