System Physiology Plant MCQ Quiz - Objective Question with Answer for System Physiology Plant - Download Free PDF

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 A gene suppresses B, which promotes flowering transition

Explanation:

• Flowering in plants is regulated by genetic pathways that involve various genes interacting with each other to control the transition from vegetative growth to flowering.
• Key Observations:
  • Wild type plants flower in 30 days, with normal transcript levels of both genes A and B.
  • In the a mutant, flowering occurs early (15 days), with no transcript of gene A and increased transcript levels of gene B.
  • In the b mutant, flowering is delayed (60 days), with normal transcript levels of gene A but no transcript of gene B.
  • In the ab double mutant, flowering is also delayed (60 days), with no transcript of either gene A or gene B.
• The data suggests that gene A normally suppresses gene B. When gene A is absent (a mutant), gene B's transcript levels increase, promoting early flowering.
• Gene B appears to be critical for promoting flowering. In its absence (b mutant), flowering is delayed significantly, regardless of the presence of gene A.
• The ab double mutant confirms that gene A does not directly promote flowering. Instead, its absence leads to increased activity of gene B, which is responsible for flowering transition. Without gene B (even when gene A is absent), flowering is delayed.
• Thus, the genetic pathway can be summarized as: Gene A suppresses gene B, which promotes the flowering transition.

The correct answer is P-1-a; Q-3-b; R-3-c

Explanation:

• Plants utilize different photosynthetic pathways for carbon fixation based on their environmental conditions. The three main pathways are the C3 cycle, C4 cycle, and CAM (Crassulacean Acid Metabolism).
• C3 Cycle:
  • The C3 cycle, also known as the Calvin cycle, is the primary photosynthetic pathway in most plants.
  • The first stable product of the C3 cycle is 3-Phosphoglycerate, a three-carbon compound.
  • Wheat is a typical example of a C3 plant, adapted to moderate climates.
• C4 Cycle:
  • The C4 cycle is an adaptation to hot and dry environments, allowing efficient carbon fixation even in low CO₂ conditions.
  • The first stable product of the C4 cycle is Oxaloacetate, a four-carbon compound.
  • Sugarcane is a prominent example of a C4 plant, showcasing its adaptation to tropical climates.
• CAM Pathway:
  • The CAM pathway is an adaptation to arid conditions, allowing plants to fix CO₂ during the night to minimize water loss.
  • Like the C4 cycle, the CAM pathway also produces Oxaloacetate as its first stable product.
  • Pineapple is a well-known CAM plant, highlighting its adaptation to water-scarce environments.

The correct answer is The source of oxygen produced in photosynthesis in green plants is CO₂

Explanation:

• Photosynthesis is the process by which green plants, algae, and certain bacteria convert light energy into chemical energy stored in glucose molecules. This process involves the use of carbon dioxide (CO₂) and an electron donor.
• In green plants, water (H₂O) acts as the electron donor, and oxygen (O₂) is released as a by-product.
• For other photosynthetic organisms, like purple sulfur bacteria, hydrogen sulfide (H₂S) or other substances may act as the electron donor, resulting in different by-products (e.g., sulfur).
• Equation 3 generalizes photosynthesis by representing the electron donor as H₂A, which can vary depending on the organism performing the process.
• Equation 1 (CO₂+H₂O →(CH₂O)+O₂  shows that the oxygen produced during photosynthesis in green plants is derived from water (H₂O), not carbon dioxide (CO₂).
• Experimental evidence, such as isotopic labeling studies, has confirmed that oxygen released during photosynthesis originates from the splitting of water molecules during the light-dependent reactions.
• Thus, the statement that CO₂ is the source of oxygen is incorrect and disproven by the generalized equation for photosynthesis (Equation 3).

The correct answer is B, C and E.

Explanation:

A. The receptors for plant steroid hormones are found in the nucleus, similar to animal steroid hormones: This statement is incorrect. Unlike animal steroid hormone receptors that are often nuclear receptors, plant steroid hormone receptors, such as those for brassinosteroids, are usually found on the cell membrane. The well-known receptor for brassinosteroids in plants is BRI1, a membrane-bound receptor kinase.
B. There are multiple pathways for the plant steroid hormone biosynthesis involving cytochrome P450 class of enzymes: This is correct. The biosynthesis of brassinosteroids, a major class of plant steroid hormones, involves multiple pathways, and several cytochrome P450 enzymes play essential roles in these pathways.
C. The first plant steroid hormone was isolated from male gametophytes: This is correct. The first brassinosteroid, brassinolide, was identified from pollen (male gametophytes) of rapeseed (Brassica napus).
D. Plants deficient for the steroid hormone brassinosteroid show underproliferation of phloem and overproliferation of xylem cells: This is incorrect. Plants deficient in brassinosteroids exhibit abnormal vascular development, characterized by reduced phloem tissue and increased xylem tissue.
E. Castasterone is a plant steroid hormone abundant in the vegetative tissues of the plant: This is correct. Castasterone is one of the active brassinosteroids and is indeed abundant in the vegetative tissues of plants.

Conclusion: Based on the analysis, the correct statements about plant steroid hormones are: B, C, and E

Explanation:

Whenever a ray of light falls on a substance, then either it reflects the light or absorbs it.

The color which is reflected by the substance appears to be its color to the human eye. All other colors are absorbed by the substance and are not visible to the eye.

Hence, when a plant with green leaves is kept in a dark room with only green light on, then it will reflect all the green light and appears brighter than the surrounding.

∴ The plant will appear brighter than the surroundings.

 The correct answer is A, D, and E.

Explanation:

Crassulacean Acid Metabolism (CAM) is an adaptation in certain plants, allowing them to conserve water by opening their stomata at night to capture CO₂ and close them during the day. 

Statement A: "The HCO₃⁻ concentration is enriched in the cytosol during the night by the CO₂ coming from the external atmosphere through the open stomata and the mitochondrial respiration."

• This is correct. At night, CAM plants open their stomata to take in CO₂, which is converted to bicarbonate (HCO₃⁻) in the cytosol. CO₂ is also generated from mitochondrial respiration.

Statement B: "Oxaloacetate produced by the action of PEPCase is stored in the vacuole during dark."

• This is incorrect. Oxaloacetate is not stored directly in the vacuole. Instead, it is rapidly converted into malate, which is stored in the vacuole during the night.

Statement C: "During light, oxaloacetate produces malate that provides CO₂ for the Calvin Benson cycle in the chloroplast."

• This is incorrect. During the day, malate (stored during the night) is decarboxylated to release CO₂, which then enters the Calvin-Benson cycle in the chloroplast. Oxaloacetate itself is not directly involved in this process during the day.

Statement D: "During dark, phosphoenolpyruvate is produced by the breakdown of starch present in the chloroplast."

• This is correct. During the night, starch is broken down to produce phosphoenolpyruvate (PEP), which is used by PEP carboxylase (PEPCase) to fix CO₂ into oxaloacetate.

Statement E: "CAM is a mechanism of concentrating CO₂ around Rubisco by keeping stomata closed during the day."

• This is correct. CAM plants concentrate CO₂ around Rubisco during the day by decarboxylating malate when the stomata are closed, thus reducing water loss.

Key Points

• HCO₃⁻ is enriched in the cytosol at night when the stomata are open.
• Malate, not oxaloacetate, is stored in the vacuole during the night and provides CO₂ during the day for the Calvin-Benson cycle.
• Phosphoenolpyruvate (PEP) is produced at night by the breakdown of starch.
• CAM plants close their stomata during the day, concentrating CO₂ around Rubisco to reduce water loss.

Fig. CAM Plant

The correct answer is Reducing sugars.

Explanation:

1. Reducing Sugars: These sugars, such as glucose and fructose, have free aldehyde or ketone groups that can participate in oxidation-reduction reactions. While they can be transported in the phloem, they are less stable over long distances due to potential for oxidation and involvement in Maillard reactions. As a result, they are not the primary form of carbon transported in the phloem.

2. Mannitol: This is a sugar alcohol that can be transported in the phloem and is stable over long distances. It is used by some plants as an osmotic agent and can help with water retention, making it suitable for transport.

3. Galactosyl-sucrose Oligosaccharides: These are forms of non-reducing sugars and are commonly found in the phloem sap. They are stable and effective for long-distance transport of carbon because they do not have reactive groups that can lead to degradation.

4. Non-reducing Sugars: These sugars, like sucrose, are preferred for long-distance transport in phloem because they are stable and do not readily participate in reactions that can lead to loss of carbon or energy.

Conclusion:

While reducing sugars can be transported, they are not ideal for long-distance transport due to their instability. In contrast, non-reducing sugars and stable compounds like mannitol and oligosaccharides are more suited for this function.

Thus, the correct answer is Reducing sugars.

The correct answer is Root water potential falls below leaf water potential at night.

Concept:

• Water potential is a measure of the potential energy of water in a system and determines the direction of water movement. Water moves from areas of higher water potential (less negative) to areas of lower water potential (more negative).

• In a well-watered plant, water generally moves from the soil (higher water potential) through the roots (moderate water potential) to the leaves (lowest water potential) due to transpiration. During a drought (like when a plant is not watered for 7 days), water potential throughout the plant becomes more negative, but the relative gradient remains the same.

Explanation:

1. Pre-dawn leaf water potential declines over the 7 days:

   • As the plant experiences water stress, leaf water potential will become more negative over time because of reduced water availability, especially at pre-dawn when transpiration is minimal. This scenario is likely to happen.

2. Leaf water potential shows a diurnal cycle of highs and lows:

   • Diurnal changes in leaf water potential are typical, with lower water potential (more negative) during the day due to transpiration and higher (less negative) water potential at night when transpiration slows. This is a common observation, so this is also likely to happen.

3. Root water potential fluctuates between day and night:

   • Water potential in the roots can fluctuate between day and night because the plant experiences changes in water uptake and soil moisture availability throughout the day, especially under water stress. So, this is likely to happen

4. Root water potential falls below leaf water potential at night:

   • This is least likely to happen because water moves from roots to leaves due to the gradient created by transpiration. Even under drought stress, the root water potential typically remains higher (less negative) than leaf water potential to allow for water flow upward. At night, when transpiration decreases, the gradient between root and leaf water potential diminishes but does not reverse.

Thus, the least likely scenario is root water potential falling below leaf water potential at night.

The correct answer is Option 3 i.e.Inactivation of ABA involves its oxidation to phaseic acid

Concept:

• ABA is stress hormone, it was first identified and characterirised while studying absicssion of cotton fruits by Frederick T. Addicott and co-workers. 
• Originally it was called abscisin II, because it was know to play an major role in abscission of fruits, another group also called it dormin because it was known to play an important role in bud dormancy. 
• ABA is a single compound inconstrast to other phytohormones like auxins, gibberellins, and cytokinins. 
• It is a 15-C Sesquiterpene compounds and it is composed on three isoprene residues. 
• It contains a cyclohexane ring consisting of keto and one hydroxy. group and a side chain that have a terminal carboxylic group.
• The position of carboxylic group at carbon 2 of the ABA determine whether it is 'cis' or ' trans' isomers of the ABA. 
• In nature, nearly all ABA occurs in cis configuration and it is also biological active form of ABA; While trans ABA is biologically inactive form.
• ABA also resembles to that of terminal portions of carotenoids. 
• ABA is synthesised in all plants cells that have chloroplast or amyloplast. 

Explanation: 

Option 1: 

• Embryo that is deficient in ABA hormone experiences precocious germination and viviparacy.
• Hence, this is an incorrect option.

Option2 :

• "Cis' form of ABA is biologically active form of ABA while trans ABA is biological inactive form of ABA. 
• Hence, this is an incorrect option. 

Option 3: 

• Cytochrome P450 monooxygenases is an important enzyme that catalyses inactivation of ABA.
• It catalyses oxidation of ABA to 8'-hydroxy ABA.
• The 8'-hydroxy ABA undergoes spontaneously isomerization and get converted to phaseic acid (PA) and then to dihydrophaseic acid (DPA).
• Hence, this is the correct option.

Option 4: 

• only early biosynthesis reaction of the ABA occurs in plastids. The last two reactions in the synthesis of ABA occurs in cytoplasm. 
• Hence, this is an incorrect option. 

Hence, the correct answer is Option 3. 

The correct answer is Malate and Aspartate

Explanation:

In C4 photosynthesis, plants use a pathway that minimizes photorespiration by fixing CO₂ into a four-carbon compound before it enters the Calvin cycle. The four-carbon intermediates that play a significant role in this process include Malate and Aspartate.

Steps in C4 Photosynthesis:

• CO2 Capture in Mesophyll Cells: The initial step in C4 photosynthesis involves the capture of CO2 in the mesophyll cells, where it reacts with phosphoenolpyruvate (PEP) to form oxaloacetate (OAA) in a reaction catalyzed by the enzyme PEP carboxylase. This reaction is the primary carboxylation step in C4 photosynthesis and occurs in the mesophyll cells.
• Conversion of OAA: The OAA can then follow different pathways, depending on the type of C4 plant. In general, OAA is either converted into malate by the enzyme malate dehydrogenase or into aspartate. Malate and aspartate serve as transport molecules to carry the fixed CO2 to the bundle sheath cells.
• Decarboxylation in Bundle Sheath Cells: Once in the bundle sheath cells, malate or aspartate undergoes decarboxylation to release CO2. The released CO2 is then fixed again by the Calvin cycle, operating in the bundle sheath cells.

Fig: A simplified schematic representation of C4 photosynthetic metabolite flow highlighting interconnectivity between bundle sheath and mesophyll metabolism.

Other Options:

• Alanine is a three-carbon amino acid, not a four-carbon compound involved in C4 photosynthesis.
• Phosphoenolpyruvate (PEP) is a three-carbon molecule, not a four-carbon intermediate.
• Pyruvate is a three-carbon molecules, not four-carbon intermediates in C4 photosynthesis.

The correct answer is Conversion of PFR to PR

Explanation:

Phytochromes are light-sensitive proteins found in plants that regulate various physiological processes in response to light. Phytochromes exist in two interconvertible forms:

• P_R (Phytochrome Red): Absorbs red light (~660 nm) and is converted to the active form P_FR.
• P_FR (Phytochrome Far-Red): Absorbs far-red light (~730 nm) and can either revert back to P_R in far-red light or undergo dark reversion in the absence of light.

Dark Reversion:

• Dark Reversion refers to the spontaneous conversion of P_FR (the active form) back to P_R (the inactive form) in the absence of light. This process occurs in the dark and serves to reset the phytochrome system in plants.

Conversion of P_R to P_FR: This happens in response to red light, not in the dark.
Export of P_FR from cytosol to nucleus: P_FR can move to the nucleus for signaling, but this is not related to dark reversion.
Export of P_R from cytosol to nucleus: P_R does not play a role in nuclear signaling and this does not describe dark reversion.