Photosynthesis MCQ Quiz in मल्याळम - Objective Question with Answer for Photosynthesis - സൗജന്യ PDF ഡൗൺലോഡ് ചെയ്യുക

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 oxygen.

Key Points

• Photosynthesis:
  • Photosynthesis definition states that the process exclusively takes place in the chloroplasts through photosynthetic pigments such as chlorophyll a, chlorophyll b, carotene, and xanthophyll.
  • All green plants and a few other autotrophic organisms utilize photosynthesis is to synthesize nutrients by using carbon dioxide, water, and sunlight.
  • The by-product of the photosynthesis process is oxygen.
  • Photosynthesis occurs when plants use light energy to convert carbon dioxide and water into glucose and oxygen.
  • Leaves contain microscopic cellular organelles known as chloroplasts.
  • Each chloroplast contains a green-colored pigment called chlorophyll.
  • Light energy is absorbed by chlorophyll molecules whereas carbon dioxide and oxygen enter through the tiny pores of stomata located in the epidermis of leaves.
  • Another by-product of photosynthesis is sugars such as glucose and fructose.
  • These sugars are used by the plants as an energy source, which helps them to grow.
  • Photosynthesis also applies to other organisms besides green plants.
  • These include several prokaryotes such as cyanobacteria, purple bacteria, and green sulfur bacteria.
  • These organisms exhibit photosynthesis just like green plants.
  • The glucose produced during photosynthesis is then used to fuel various cellular activities.
  • The by-product of this physio-chemical process is oxygen.

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 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:

• The Triose-Phosphate Translocator (TPT) and Xylulose 5-Phosphate Translocator (XPT) are crucial transporters in plants that facilitate the exchange of metabolites between the chloroplast and cytosol.
• The TPT primarily exports triose phosphate (e.g., glyceraldehyde-3-phosphate) from the chloroplast to the cytosol during photosynthesis in exchange for inorganic phosphate (Pi).
• The XPT is responsible for the transport of pentose phosphates, including xylulose 5-phosphate, between the chloroplast and cytosol, which are essential intermediates in the pentose phosphate pathway and Calvin-Benson cycle.
• If both TPT and XPT are inhibited, the metabolites they normally transport will accumulate in the chloroplast, as they cannot be exported to the cytosol.

Explanation:

• Triose phosphate accumulation in the chloroplast: When the Triose-Phosphate Translocator (TPT) is inhibited, triose phosphate (e.g., glyceraldehyde-3-phosphate) cannot be exported to the cytosol. As a result, it accumulates in the chloroplast. This aligns with assumption A.
• Xylulose 5-phosphate accumulation in the chloroplast: XPT is primarily involved in retrieving pentose phosphates, including xylulose 5 phosphate, from the extraplastidial space and making them available to the plastids. If XPT is inhibited, xylulose 5-phosphate would accumulate more in the cytosol because it cannot be efficiently transported into the chloroplast. This aligns with assumption D.

Therefore, the correct combination of assumptions is A and D.

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.

The correct answer is A, B and D

Explanation:

A. Expression of the plastid-localized Glutamine Synthetase (GS) gene is upregulated by light.

• Correct. Glutamine Synthetase (GS) is an important enzyme in nitrogen assimilation, and its expression is known to be regulated by light.
•  Light plays a critical role in photosynthesis, providing energy through the production of ATP and NADPH. These energy molecules are essential for many biosynthetic pathways, including the synthesis of amino acids.
• The increased activity of photosynthesis under light conditions provides more ATP and reduced carbon, which can be linked to the upregulation of genes encoding for GS. Hence, light positively influences the expression of the plastid-localized GS gene.

B. Darkness promotes the expression of Asparagine Synthetase (AS) gene.

• Correct. Asparagine Synthetase (AS) is involved in nitrogen storage and transport. Its expression tends to be upregulated in the dark when carbon fixation via photosynthesis is halted.
• In the absence of light (darkness), photosynthetic activity ceases, reducing the availability of ATP and NADPH.
• Under these conditions, plants need to manage and store nitrogen efficiently. The upregulation of AS in darkness allows for the storage of nitrogen in the form of asparagine, facilitating this management.
• Thus, darkness acts as a signal to increase the expression of the AS gene to adapt to the reduced availability of energy and carbon from photosynthesis.

C. Expression of GS is inhibited by sucrose while that of AS is upregulated by sucrose.

• Incorrect. Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine.
  The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.Glutamine Synthetase (GS) plays a key role in the assimilation of ammonium by converting it into glutamine. The regulation of GS is critically dependent on nitrogen status rather than directly on sucrose levels. Sucrose acts more as a carbon source and signal that impacts overall plant metabolism rather than specifically inhibiting GS expression.
• Asparagine Synthetase (AS) converts aspartate and glutamine into asparagine, which serves as a nitrogen transport and storage compound. The expression of AS can be influenced by the carbon/nitrogen balance in plants. High carbon availability (e.g., from sucrose) can signal the need to store nitrogen during periods when carbon is abundant, which might promote AS expression.
• While sucrose can play a role in signaling pathways that impact various aspects of plant metabolism, the direct inhibition of GS by sucrose and upregulation of AS specifically by sucrose is not evident.

D. Asparagine is a more efficient carbon source than glutamine.

• Correct. Asparagine is a molecule that can be transported and stored more efficiently in plants compared to glutamine.
• It contains a higher nitrogen-to-carbon ratio, making it a suitable molecule for long-term nitrogen storage and transport.
• As a carbon source, asparagine's structure allows it to release its carbon more effectively during metabolic processes, providing a steady supply of carbon skeletons for various biosynthetic pathways.

Conclusion: The correct statements are A, B, and D. ​

The correct answer is dry tropical region.

Explanation:

C4 photosynthesis is most prevalent in plants found in dry tropical regions. These regions are characterized by high temperatures, intense sunlight, and often limited water availability. The C4 pathway allows plants to maintain high photosynthetic efficiency while conserving water, making it an ideal adaptation for survival in these challenging conditions.

Other Options:

1: Cold Region: C4 photosynthesis is not common in plants found in cold regions. Cold environments typically do not present the high levels of light intensity and temperature that C4 plants require. C4 plants are adapted to reduce photorespiration, a process that occurs at higher temperatures, making the C4 pathway less advantageous in cold climates. Therefore, C3 photosynthesis, which is more efficient under cooler and moister conditions, is more common in these regions.

2: Hot Region: C4 photosynthesis is well-suited to hot regions because the C4 pathway is an adaptation to high temperatures. In hot conditions, plants with a C3 photosynthetic pathway suffer from high rates of photorespiration, which decreases their efficiency. C4 plants, on the other hand, have a mechanism to concentrate CO₂ in specialized cells (bundle sheath cells), reducing photorespiration and allowing them to thrive in hot environments.

3: Both (1) and (2): This option suggests that C4 plants are found in both cold and hot regions, which is incorrect. As explained, C4 plants are adapted to hot, sunny environments where they can minimize water loss and reduce photorespiration, not cold regions.