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

The correct answer is Sucrose in cytosol and starch in chloroplasts

Concept:

• Photosynthesis is the process through which plants, algae, and some bacteria convert light energy into chemical energy, producing glucose and oxygen from carbon dioxide and water.
• The glucose produced during photosynthesis can be further processed into sucrose and starch, which serve as energy storage molecules.
• Sucrose and starch are produced in different cellular compartments, ensuring efficient distribution and storage of the photosynthetic products.

Explanation:

• Sucrose in cytosol and starch in chloroplasts: This is the correct answer. Sucrose is synthesized in the cytosol, where it is readily available for transport to other parts of the plant. Starch, on the other hand, is synthesized and stored in the chloroplasts, where it can be used as an energy reserve.

Fig:Mechanisms of sucrose and triose-phosphate export from the chloroplast to the cytosol 

• Sucrose in cytosol and starch in mitochondria: This option is incorrect because starch is not synthesized or stored in mitochondria. Mitochondria are primarily involved in cellular respiration and energy production.
• Sucrose in chloroplasts and starch in cytosol: This option is incorrect because sucrose is not synthesized in chloroplasts. Sucrose synthesis occurs in the cytosol, while starch synthesis and storage occur within the chloroplasts.
• Sucrose in mitochondria and starch in cytosol: This option is incorrect because neither sucrose nor starch are synthesized or stored in mitochondria. Mitochondria are involved in energy production, not in the synthesis or storage of these molecules.

The correct answer is Option 4 i.e. A and D.

Explanation-

Statement A is correct as Nitrogen is taken in the form of Nitric oxide and Nitrous oxide which is further reduced by the process of Nitogen metabolism & assimilation.According to this option 3 is incorrect. Nitrate reductase are molybdo-enzymes that reduce nitrate (NO₃⁻) to nitrite (NO₂⁻), it does not involve Mg rather includes FAD, Mo & Heme as co-factors.

Key PointsThe correct combination of statements regarding the capability of biological nitrogen reduction in the plant kingdom and many bacteria is:

A. Nitrogen is normally taken by the plant in their fully oxidized form but needs to be reduced before incorporation into organic molecules: This statement is correct. Plants typically take up nitrogen in the form of nitrate (NO3−) or ammonium (NH₄⁺), and these need to be reduced to form amino acids and other organic molecules.

B. Conversion of oxidized nitrogen into reduced nitrogen needs energy in the form of NAD(P)⁺:This statement is not accurate. While energy is required for the reduction of oxidized nitrogen, the specific cofactor involved is NAD(P)H (reduced form of nicotinamide adenine dinucleotide phosphate) rather than NAD(P)⁺. The process of reducing nitrate (NO3−) to ammonium (NH₄⁺) involves the transfer of electrons, and NAD(P)H is commonly used as a source of electrons for this reduction.

C.The metal associated with the enzyme nitrate reductase is Magnesium" is incorrect. Nitrate reductase, an enzyme involved in the reduction of nitrate (NO3−) to nitrite (NO₂^-) during nitrogen metabolism, typically contains molybdenum (Mo) as a cofactor, not magnesium (Mg).

D. Nitrate reduction takes place in the cytoplasm, whereas nitrite reduction takes place in chloroplast matrix: This statement is correct. Nitrate reduction (conversion of nitrate to nitrite) generally occurs in the cytoplasm, while nitrite reduction (further reduction to ammonium) can take place in various cellular compartments, including chloroplasts.

The correct answer is Option 2 and 3

Explanation:

• Phosphoenolpyruvate carboxylase (PEPC or PEPCase) is a vital enzyme in the process of CO₂ fixation in both C4 and crassulacean acid metabolism (CAM) plants.
• The regulation of this enzyme is crucial for the efficient functioning of their respective photosynthetic pathways, which differ significantly in how and when they fix CO₂.
• The activity of PEPCase is regulated by several mechanisms, including phosphorylation and dephosphorylation, which can activate or deactivate the enzyme, respectively.

A. PEPCase in C4 plants is inactivated by dephosphorylation during the day.

• Incorrect. In C4 plants, PEPCase is involved in CO₂ fixation during the day. The enzyme is typically activated in the light via phosphorylation to fix CO2 efficiently into oxaloacetate, which is then converted to malate and transported to bundle sheath cells for further processing. The statement contradicts the typical regulation of PEPCase in C4 photosynthesis.

B. PEPCase in CAM plants is inactivated by dephosphorylation during the day.

• Correct. CAM plants have a unique mechanism where they open their stomata and fix CO₂ during the night to minimize water loss.
• This CO₂ is fixed into organic acids (like malate) by PEPCase, which is active (often phosphorylated and thus activated) at night.
• During the day, when the CAM plants close their stomata to minimize water loss, the fixed carbon is released from the organic acids for photosynthesis, and PEPCase activity is reduced (often through dephosphorylation).

C. PEPCase in C4 plants is inactivated by dephosphorylation at night.

• Correct. PEPCase in C4 plants is primarily active during the day for CO₂ fixation. Therefore, it implies there is less need for its activity at night, suggesting it could be in a less active form (i.e., dephosphorylated).
• However, the exact regulation of PEPCase by dephosphorylation at night in C4 plants is not typically emphasized in literature as much as its activation during the day.

D. PEPCase in CAM plants is inactivated by dephosphorylation at night.

• Incorrect. In CAM plants, PEPCase is actually activated at night (often through phosphorylation) to fix CO₂ into organic acids. This statement contradicts the fundamental mechanism of CAM photosynthesis.

Conclusion:

Therefore, the correct statements are B and C

The correct answer is A,C and E

Explanation:

The biosynthesis of jasmonic acid in plants involves several steps, occurring in different cellular compartments, primarily the chloroplasts and peroxisomes.These steps include the action of various enzymes like lipoxygenase (LOX), allene oxide synthase (AOS), and allene oxide cyclase (AOC), as well as processes like β-oxidation. Based on the statements provided:

• A. 12-oxo-phytodienoic acid is produced in chloroplast and transported to peroxisome. - This statement is correct. The precursor to jasmonic acid, 12-oxo-phytodienoic acid (OPDA), is indeed produced in the chloroplast and then transported to the peroxisome for further processing.
• B. Action of lipoxygenase, allene oxide synthase and allene oxide cyclase takes place in peroxisome. - This statement is incorrect. The action of lipoxygenase (LOX) takes place in the chloroplasts, initiating the pathway. The action of allene oxide synthase (AOS) and allene oxide cyclase (AOC) also primarily takes place in the chloroplast, not the peroxisome.
• C. 12-oxo-phytodienoic acid is first reduced and then converted to jasmonic acid by β-oxidation. - This statement is correct. In the peroxisome, 12-oxo-phytodienoic acid (OPDA) undergoes reduction and is then subjected to β-oxidation to produce jasmonic acid.
• D. Final production of jasmonic acid takes place in chloroplast. - This statement is incorrect. The final production of jasmonic acid, after the β-oxidation steps, occurs in the peroxisome.
• E. Action of allene oxide synthase and allene oxide cyclase takes place in chloroplast. - This statement is correct. Both allene oxide synthase (AOS) and allene oxide cyclase (AOC), which are involved in the early steps of jasmonic acid synthesis, act in the chloroplast.

Key Points

• During photorespiration, the oxidation of glycolate to glyoxylate primarily takes place in the peroxisomes within plant cells. 

Glycolate Formation:

• Photorespiration begins when the enzyme RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the oxygenation of ribulose-1,5-bisphosphate instead of its carboxylation.
• This results in the formation of a two-carbon compound called glycolate.

Transport to Peroxisomes:

• Glycolate is then transported from the chloroplasts, where it is produced, to the peroxisomes, which are specialized organelles within plant cells.

Oxidation in Peroxisomes:

• In the peroxisomes, glycolate is subjected to a series of enzymatic reactions that lead to its oxidation to glyoxylate.
• Key enzymes involved in this process include glycolate oxidase and glyoxylate aminotransferase.

Glycolate Oxidase:

• This enzyme catalyzes the conversion of glycolate into glyoxylate, producing hydrogen peroxide (H₂O₂) as a byproduct.​

Glyoxylate Aminotransferase:

• Glyoxylate produced in the peroxisomes can then be converted into other compounds, such as glycine, through the action of glyoxylate aminotransferase.
• This is part of the glyoxylate detoxification pathway, which helps prevent the accumulation of toxic glyoxylate.

Transport of Metabolites:

• The resulting metabolites, including glycine, can be transported back to the chloroplasts, where they participate in the photorespiratory cycle.

Explanation:

• The peroxisomes play a crucial role in photorespiration by facilitating the initial oxidation of glycolate to glyoxylate.
• This process is essential for the plant to recover some of the carbon and energy lost during oxygenation by RuBisCO in the chloroplasts, ultimately contributing to the plant's survival in oxygen-rich environments.

Hence the correct answer is option 1.

Key Points

• The oxidative pentose phosphate pathway (also known as the pentose phosphate shunt or the phosphogluconate pathway) is a metabolic pathway that operates alongside glycolysis in the cytoplasm of cells.
• It is an alternative route for the metabolism of glucose-6-phosphate, distinct from glycolysis.
• The pathway serves two main purposes:
  • the production of NADPH (reducing equivalent) and
  • the generation of ribose-5-phosphate for nucleotide biosynthesis.
• The oxidative pentose phosphate pathway consists of two phases:
  • the oxidative phase and
  • the non-oxidative phase.
• Oxidative Phase:
  • The oxidative phase involves a series of reactions that generate NADPH and ribose-5-phosphate.
  • Glucose-6-phosphate is converted to ribulose-5-phosphate through a series of reactions catalyzed by glucose-6-phosphate dehydrogenase, 6-phosphogluconolactonase, and 6-phosphogluconate dehydrogenase.
  • NADP+ is reduced to NADPH in these reactions, providing the reducing equivalents required for anabolic processes.
• Non-oxidative Phase:
  • The non-oxidative phase involves interconversion reactions of several sugar phosphates.
  • Ribulose-5-phosphate can be converted to other sugars like ribose-5-phosphate, xylose-5-phosphate, or sedoheptulose-7-phosphate, which are important for nucleotide and coenzyme synthesis.

Important Points

• Regulation and Control:
•  The oxidative pentose phosphate pathway is regulated by the availability of NADP+ and NADPH.
  The rate-limiting enzyme of the pathway is glucose-6-phosphate dehydrogenase, which is allosterically activated by NADP+ and inhibited by NADPH.

• In the oxidative pentose phosphate pathway, the translocation of glutamate from the cytosol to the leucoplast is not directly associated with this pathway.
• The oxidative pentose phosphate pathway primarily involves the metabolism of glucose-6-phosphate to produce NADPH and ribose-5-phosphate, as mentioned earlier.

• Alpha-ketoglutarate is an intermediate metabolite in the tricarboxylic acid (TCA) cycle, also known as the citric acid cycle or Krebs cycle. It plays a central role in cellular metabolism by participating in the oxidation of carbohydrates, fats, and amino acids to produce energy in the form of ATP.
• In the oxidative pentose phosphate pathway, alpha-ketoglutarate is not directly involved, and there is no specific translocation of alpha-ketoglutarate from the cytosol to the leucoplast associated with this pathway.

• In certain plant cells, glucose-6-phosphate can indeed be translocated from leucoplasts to the cytosol to participate in the oxidative pentose phosphate pathway (OPPP).
• Leucoplasts are plastids found in plant cells that are involved in various metabolic processes, including the synthesis and storage of starch.
• During the OPPP, glucose-6-phosphate is converted to 6-phosphogluconolactone by the enzyme glucose-6-phosphate dehydrogenase (G6PDH).
• In some plants, G6PDH is found in the cytosol, while in others, it is localized in the leucoplasts.
• In plants where G6PDH is present in leucoplasts, glucose-6-phosphate must be translocated from the leucoplasts to the cytosol for the continuation of the pathway.
• After translocation to the cytosol, 6-phosphogluconolactone is further converted to ribulose-5-phosphate through a series of enzymatic reactions.
• This ribulose-5-phosphate can then enter various metabolic pathways, including the synthesis of nucleotides and other important cellular constituents.

Statement D: INCORRECT

• This statement is not true, consider explanation above

Concept:

• Nitrogen is an essential macronutrient for plant growth and development.
• It is a key component of amino acids, which are the building blocks of proteins, as well as nucleic acids, which are essential for genetic material.
• Nitrogen is also a component of chlorophyll, which is necessary for photosynthesis, the process by which plants convert sunlight into energy.
• Nitrogen availability can vary depending on a number of factors, including soil type, temperature, moisture, and the presence of microorganisms.
• Nitrogen can be present in the soil in various forms, including organic nitrogen and inorganic nitrogen.
• Organic nitrogen is present in the form of plant and animal residues, while inorganic nitrogen is present in the form of ammonium and nitrate ions.
• To increase the availability of nitrogen to plants, fertilizers can be applied to the soil.
• Common nitrogen-containing fertilizers include ammonium nitrate, urea, ammonium sulfate, and others.
• When these fertilizers are applied to the soil, they are broken down into ammonium or nitrate ions, which can be taken up by plant roots.

Explanation:

• Urea is a nitrogen-containing fertilizer that is commonly used in agriculture to supplement the nitrogen available to plants.
• When urea is applied to the soil, it is converted to ammonium ions through a process called hydrolysis.
• Ammonium ions can then be taken up by the plant roots and used for various metabolic processes.
• Urea is a highly concentrated nitrogen source, and its availability to plants depends on several factors such as soil type, temperature, moisture, and microbial activity.
• In some cases, the conversion of urea to ammonium ions can be slow, leading to reduced nitrogen availability in the short term.

Concept:

• In plants and all other oxygenic phototrophs, photorespiration is a multienzyme bypass to the CO2-fixation process of the Calvin-Benson cycle.
• The purpose of this bypass is to eliminate and recycle 2-phosphoglycolate, a toxic byproduct of photosynthesis that is created when O2 replaces CO2 in the CO2-fixation reaction.
• Formally, one molecule of 3-phosphoglycerate, which enters the Calvin-Benson cycle, and one molecule of CO2, which is refixed or lost to the environment, are created from two molecules of 2-phosphoglycolate.
• Photorespiration occurs in both peroxisomes and mitochondria.
• RuBP + O2 → 2-Phosphoglycolate (2PG) + 3-phosphoglycerate (3PG) + 2H+ (photorespiration equation)

Explanation:

Statement A: Photorespiration takes place in only C3 plants.

• C3 plants begin to photorespirate when the CO2 level falls to about 50 ppm. The primary enzyme responsible for fixing carbon is called rubisco, and at low levels of CO2 it starts to fix oxygen instead.
• When C3 plants are adequately watered in settings of moderate temperature, there is an abundant supply of carbon dioxide and photorespiration is not an issue.
• However, in hot and dry weather, the stomata shut to stop excessive water loss, and the Calvin cycle's ongoing fixation of carbon significantly lowers the relative content of CO2.
• Around 50 ppm is considered the threshold amount at which the rubisco stops fixing CO2 and starts fixing O2. Rubisco operates at just approximately 25% of its ideal rate due to the photorespiration process, despite the detoured process feeding some PGA back into the cycle.
• So , this statement is true.

Statement B: Photorespiration takes place in only C4 plants.

• By utilising an additional enzyme termed PEP carboxylase during the initial stage of carbon fixation, C4 plants, such as maize, sugarcane, and sorghum, avoid photorespiration.
• This process happens in the mesophyll cells, which are close to the stomata where oxygen and carbon dioxide enter the plant.
• PEP carboxylase is far less likely to react with oxygen molecules since it is more attracted to carbon dioxide molecules.
• Malate, a four-carbon chemical that PEP enzyme uses to fix carbon dioxide, is delivered to the deeper bundle sheath cells where Rubisco is found.
• Without having to deal with the oxygen molecules that are present in large quantities in the mesophyll cells, the malate is subsequently broken down into a compound that is recycled back into PEP and carbon dioxide that Rubisco binds into sugars.
• So, this statement is untrue.

Statement C: Photorespiration takes place in both C3 and C4 plants.

• both the plants do exhibit photorespiration however it is predominant in C3 plants and negligible in C4 plants hence this statement is untrue.

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Statement D: Glycolate is oxidized to glyoxylate in the peroxisome.

Steps in photorespiration:

1.  The 2PG formed in the chloroplast by the oxygenase activity of RuBisCO is first dephosphorylated to glycolate.
2.  Glycolate is then transported from the chloroplast to the peroxisome. It is then metabolized to glyoxylate by the enzyme glycolate oxidase
3.  This reaction consumes O2 and generates a toxic molecule, H2O2, later detoxified by the enzyme catalase, regenerating O2.

hence this statement is true.

Statement E: Glycolate is oxidized to glyoxylate in the mitochondira.

• since the above statement is true this statement in untrue.

​So, the correct combination is statement A and D so option 1 is correct.

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