Photosynthesis

Topic: Calvin Cycle and Carbon Fixation; Subtopic: Role of RuBisCO in Photosynthesis

Keyword Definitions:

• RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme that catalyzes the fixation of CO2 in the Calvin cycle.

• RuBP: Ribulose-1,5-bisphosphate, the five-carbon compound that reacts with CO2 during carbon fixation.

• Calvin cycle: The light-independent phase of photosynthesis that converts CO2 into glucose.

• Carboxylation: The addition of CO2 to an organic compound, catalyzed by enzymes such as RuBisCO.

Lead Question – 2025

Which of the following statement about RuBisCO is true?

(1) It is active only in the dark

(2) It has higher affinity for oxygen than carbon dioxide

(3) It is an enzyme involved in the photolysis of water

(4) It catalyzes the carboxylation of RuBP

Explanation: RuBisCO catalyzes the carboxylation of RuBP during the first step of the Calvin cycle. It fixes CO2 to form two molecules of 3-phosphoglyceric acid. Although it also shows oxygenase activity, its carboxylase function is primary in photosynthesis. Hence, option (4) is correct as it performs carboxylation, not photolysis or dark activity.

1. RuBisCO enzyme is found in which part of the chloroplast?

(1) Thylakoid membrane

(2) Inner membrane

(3) Stroma

(4) Intermembrane space

Explanation: RuBisCO is located in the stroma of the chloroplast, where the Calvin cycle reactions occur. The enzyme catalyzes the fixation of carbon dioxide into organic molecules. The stroma provides the necessary environment and substrates like RuBP for carbon fixation in the light-independent stage of photosynthesis.

2. The primary function of RuBisCO during photosynthesis is:

(1) Water splitting

(2) Carbon fixation

(3) ATP formation

(4) Oxygen production

Explanation: The main role of RuBisCO is carbon fixation in the Calvin cycle. It catalyzes the reaction between RuBP and CO2 to form 3-PGA. This reaction marks the first step of converting inorganic carbon into organic molecules essential for plant growth and carbohydrate synthesis.

3. RuBisCO can act as:

(1) Only carboxylase

(2) Only oxygenase

(3) Both carboxylase and oxygenase

(4) Neither carboxylase nor oxygenase

Explanation: RuBisCO exhibits dual activity—it acts as both a carboxylase and an oxygenase. In the presence of high CO2 concentration, it functions as a carboxylase, but when O2 concentration is higher, it acts as an oxygenase, leading to photorespiration, which reduces photosynthetic efficiency.

4. The enzyme RuBisCO becomes inefficient during photorespiration because:

(1) It is destroyed by light

(2) It binds to O2 instead of CO2

(3) It stops working in high CO2

(4) It produces more glucose than needed

Explanation: During photorespiration, RuBisCO binds with O2 instead of CO2 due to its oxygenase activity. This results in the production of phosphoglycolate, which must be recycled, consuming ATP and releasing CO2. Thus, the process decreases photosynthetic efficiency in plants.

5. In C3 plants, RuBisCO is located in:

(1) Mesophyll cells

(2) Bundle sheath cells

(3) Both A and B

(4) Guard cells only

Explanation: In C3 plants, RuBisCO is present in the chloroplasts of mesophyll cells, where the Calvin cycle operates. C4 plants, however, have RuBisCO localized in bundle sheath cells to minimize photorespiration, enhancing carbon fixation efficiency under high light and temperature conditions.

6. Which of the following reactions is catalyzed by RuBisCO?

(1) CO2 + RuBP → 2 × 3-PGA

(2) H2O → ½O2 + 2H+

(3) ADP + Pi → ATP

(4) NADP+ → NADPH

Explanation: RuBisCO catalyzes the fixation of CO2 to RuBP forming two molecules of 3-phosphoglyceric acid (3-PGA). This reaction is the entry point of CO2 into the Calvin cycle, marking the synthesis of organic compounds from inorganic carbon in the stroma of chloroplasts.

Assertion–Reason Type Question

7. Assertion (A): RuBisCO is the most abundant enzyme on Earth.

Reason (R): It is present in all photosynthetic organisms.

(1) Both A and R are true, and R is the correct explanation of A.

(2) Both A and R are true, but R is not the correct explanation of A.

(3) A is true, R is false.

(4) A is false, R is true.

Explanation: Both assertion and reason are true, and R correctly explains A. RuBisCO is the most abundant enzyme due to its presence in all photosynthetic organisms—plants, algae, and cyanobacteria. Its global abundance reflects its crucial role in carbon fixation and biomass production on Earth.

Matching Type Question

8. Match List-I with List-II:

A. RuBisCO  I. Carbon fixation

B. ATP synthase II. ATP production

C. NADP+ reductase III. NADPH formation

D. PEP carboxylase IV. C4 carbon fixation

(1) A-I, B-II, C-III, D-IV (2) A-II, B-I, C-IV, D-III (3) A-IV, B-I, C-II, D-III (4) A-III, B-IV, C-I, D-II

Explanation: The correct match is A-I, B-II, C-III, D-IV. RuBisCO fixes CO2 in the Calvin cycle, ATP synthase forms ATP during photophosphorylation, NADP+ reductase generates NADPH, and PEP carboxylase fixes CO2 in C4 plants. Each enzyme plays a key role in photosynthetic energy conversion.

Fill in the Blanks / Completion Type Question

9. RuBisCO catalyzes the conversion of RuBP and _______ into 3-PGA.

(1) O2

(2) CO2

(3) H2O

(4) NADPH

Explanation: RuBisCO catalyzes the reaction between CO2 and RuBP to form two molecules of 3-phosphoglyceric acid (3-PGA). This is the first stable product of the Calvin cycle, representing the fixation of inorganic carbon into an organic form used for glucose synthesis.

Choose the Correct Statements Type Question

10. Statement I: RuBisCO functions as both carboxylase and oxygenase.

Statement II: Its oxygenase activity increases photorespiration.

(1) Both statements are correct.

(2) Both statements are incorrect.

(3) Only Statement I is correct.

(4) Only Statement II is correct.

Explanation: Both statements are correct. RuBisCO acts as a carboxylase under high CO2 concentration and as an oxygenase under high O2 conditions. The oxygenase activity triggers photorespiration, leading to CO2 loss and reduced photosynthetic efficiency, particularly in C3 plants under high temperature and light.

Topic: Pigments Involved in Photosynthesis; Subtopic: Types of Chlorophylls and Accessory Pigments

Keyword Definitions:

• Chlorophyll: Green pigment in plants that captures light energy for photosynthesis.

• Xanthophyll: Yellow accessory pigment aiding in light absorption and photoprotection.

• Carotenoids: Pigments providing yellow to orange color, protecting chlorophyll from photo-damage.

• Accessory Pigments: Molecules that transfer absorbed light energy to chlorophyll for photosynthesis.

Lead Question – 2025

Match List - I with List - II
List - I            List - II
A. Chlorophyll a          I. Yellow - green
B. Chlorophyll b          II. Yellow
C. Xanthophylls          III. Blue - green
D. Carotenoids          IV. Yellow to Yellow - orange

Choose the option with all correct matches
(1) A-III, B-IV, C-II, D-I
(2) A-III, B-I, C-II, D-IV
(3) A-I, B-II, C-IV, D-III
(4) A-I, B-IV, C-III, D-II

Explanation: The correct answer is (2) A-III, B-I, C-II, D-IV. Chlorophyll a appears blue-green, the chief pigment for photosynthesis. Chlorophyll b is yellow-green and acts as an accessory pigment. Xanthophylls are yellow, while carotenoids range from yellow to orange. Together, they broaden the absorption spectrum and enhance light energy utilization efficiently in plants.

Guessed Questions:

1. Which pigment primarily absorbs red and blue wavelengths of light?
(1) Chlorophyll a (2) Chlorophyll b (3) Xanthophyll (4) Carotene
Explanation: Chlorophyll a absorbs mainly red and blue light and reflects green, giving plants their color. It is the chief pigment that initiates the photochemical reactions of photosynthesis by converting light energy into chemical energy, while accessory pigments broaden the absorption range of light.

2. Which pigment acts as a photoprotective pigment preventing photooxidative damage?
(1) Chlorophyll b (2) Xanthophyll (3) Pheophytin (4) Phycobilin
Explanation: Xanthophyll acts as a photoprotective pigment, dissipating excess absorbed light energy as heat. This prevents damage to chlorophyll and the photosynthetic machinery, especially under high light intensity. It belongs to the carotenoid family and contributes to the yellow coloration of leaves in some plants.

3. **Fill in the Blanks Type:** The photosynthetic pigment that appears blue-green is _________.
(1) Chlorophyll a (2) Chlorophyll b (3) Xanthophyll (4) Carotene
Explanation: The correct answer is Chlorophyll a. It gives the blue-green color to plant tissues and plays the primary role in photosynthesis. Chlorophyll a is found in all oxygenic photosynthetic organisms and directly participates in the conversion of light energy into chemical energy.

4. In higher plants, which pigment captures light and transfers energy to chlorophyll a?
(1) Xanthophyll (2) Chlorophyll b (3) Carotenoid (4) Both 2 and 3
Explanation: The correct answer is (4) Both 2 and 3. Chlorophyll b and carotenoids function as accessory pigments, capturing additional light wavelengths not absorbed by chlorophyll a. They efficiently transfer this energy to chlorophyll a to maximize photosynthetic light utilization and efficiency in plants.

5. Which of the following pigments is not a carotenoid?
(1) Lutein (2) Zeaxanthin (3) Chlorophyll a (4) β-carotene
Explanation: The correct answer is (3) Chlorophyll a. Carotenoids include pigments like β-carotene, lutein, and zeaxanthin, which absorb light in the blue and green regions. They protect chlorophyll from oxidative damage and assist in light absorption but are chemically distinct from chlorophyll pigments.

6. **Assertion-Reason Type:**
Assertion (A): Chlorophyll b broadens the absorption spectrum of photosynthesis.
Reason (R): Chlorophyll b absorbs mainly blue and red light.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true but R is false.
(4) Both A and R are false.
Explanation: The correct answer is (2). Chlorophyll b indeed broadens the spectrum of photosynthesis but mainly absorbs blue and orange light, not red. It transfers absorbed light energy to chlorophyll a, enhancing photosynthetic efficiency under different light conditions in plants.

7. **Matching Type:** Match the pigment with its characteristic absorption color.
A. Chlorophyll a – (i) Blue-green
B. Chlorophyll b – (ii) Yellow-green
C. Carotene – (iii) Orange
D. Xanthophyll – (iv) Yellow
(1) A-i, B-ii, C-iii, D-iv
(2) A-ii, B-i, C-iv, D-iii
(3) A-iii, B-ii, C-i, D-iv
(4) A-i, B-iii, C-ii, D-iv
Explanation: The correct answer is (1). Each pigment has distinct absorption properties — Chlorophyll a (blue-green), Chlorophyll b (yellow-green), Carotene (orange), and Xanthophyll (yellow). These diverse absorption peaks allow plants to efficiently utilize the solar spectrum for photosynthesis.

8. **Choose the Correct Statements Type:**
Statement I: Carotenoids protect chlorophyll from photooxidation.
Statement II: Chlorophyll a acts only as an accessory pigment.
(1) Both I and II correct
(2) I correct, II incorrect
(3) I incorrect, II correct
(4) Both incorrect
Explanation: The correct answer is (2). Carotenoids indeed protect chlorophyll from photooxidative stress, but Chlorophyll a is the primary pigment, not accessory. It forms the reaction center of photosystems and drives the photochemical steps of photosynthesis efficiently.

9. Which pigment gives the characteristic autumn yellow color in leaves?
(1) Chlorophyll a (2) Carotenoids (3) Anthocyanin (4) Chlorophyll b
Explanation: The correct answer is (2) Carotenoids. During autumn, chlorophyll degrades, and the yellow-orange carotenoids become visible. These pigments are stable and contribute to the bright fall foliage colors in deciduous plants, reflecting the hidden beauty of accessory pigments in nature.

10. Which of the following statements regarding chlorophyll is correct?
(1) Contains iron in its porphyrin ring
(2) Contains magnesium in its center
(3) Found only in cyanobacteria
(4) Absorbs green wavelength strongly
Explanation: The correct answer is (2). Chlorophyll molecules contain magnesium at the center of their porphyrin ring structure. This central metal ion is crucial for capturing light energy and initiating the process of photosynthesis, ensuring efficient energy conversion and electron transfer.

Topic: Calvin Cycle; Subtopic: ATP and NADPH Requirement in CO₂ Fixation

Keyword Definitions:

• Calvin Cycle: The series of light-independent reactions in photosynthesis that convert CO₂ into glucose using ATP and NADPH.

• ATP (Adenosine Triphosphate): The energy currency of cells, providing energy for biochemical reactions.

• NADPH: A reducing agent that donates high-energy electrons during CO₂ fixation in the Calvin cycle.

• CO₂ Fixation: The process by which carbon dioxide is converted into organic compounds like sugars in plants.

• RUBP (Ribulose-1,5-bisphosphate): A five-carbon compound that reacts with CO₂ to initiate the Calvin cycle.

Lead Question - 2024 (Jhajjhar)
How many molecules of ATP and NADPH are required respectively for fixation of every CO₂ molecule entering the Calvin cycle?
1. 2 and 4
2. 4 and 2
3. 3 and 2
4. 2 and 3

Explanation: The Calvin cycle requires 3 ATP and 2 NADPH molecules to fix one molecule of CO₂ into a carbohydrate. ATP provides the energy for phosphorylation reactions, while NADPH provides reducing power for converting 3-phosphoglycerate into glyceraldehyde-3-phosphate. This process occurs in the stroma of chloroplasts during the light-independent phase of photosynthesis.

1. Which enzyme catalyzes the first reaction of the Calvin cycle?
1. RUBISCO
2. PEP carboxylase
3. ATP synthase
4. Hexokinase

Explanation: The enzyme RUBISCO (Ribulose-1,5-bisphosphate carboxylase-oxygenase) catalyzes the first reaction of the Calvin cycle, combining CO₂ with ribulose-1,5-bisphosphate to form two molecules of 3-phosphoglycerate. RUBISCO is the most abundant enzyme on Earth and is crucial for photosynthetic carbon fixation in plants and algae.

2. In which part of the chloroplast does the Calvin cycle take place?
1. Thylakoid lumen
2. Stroma
3. Grana
4. Inner membrane space

Explanation: The Calvin cycle occurs in the stroma of chloroplasts, where enzymes necessary for carbon fixation and carbohydrate synthesis are located. The stroma is the fluid-filled space surrounding the thylakoids and serves as the site of light-independent reactions, utilizing ATP and NADPH produced during the light-dependent phase.

3. The product of the Calvin cycle which acts as a precursor for glucose formation is:
1. 3-Phosphoglycerate
2. Glyceraldehyde-3-phosphate (G3P)
3. Pyruvate
4. Fructose-6-phosphate

Explanation: The immediate product of the Calvin cycle is glyceraldehyde-3-phosphate (G3P), a three-carbon compound. Two molecules of G3P combine to form one glucose molecule. G3P acts as the central intermediate linking carbon fixation to carbohydrate biosynthesis, providing the carbon skeleton for sugars and other biomolecules.

4. Assertion-Reason Type Question:
Assertion (A): Calvin cycle is also known as the C₃ pathway.
Reason (R): The first stable product of CO₂ fixation is a 3-carbon compound, 3-phosphoglycerate.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Explanation: The correct answer is option 1. The Calvin cycle is called the C₃ pathway because the first stable product after CO₂ fixation is 3-phosphoglycerate (a 3-carbon compound). This pathway operates in C₃ plants such as wheat, rice, and barley and is responsible for the majority of global carbon fixation.

5. Match the following:
A. Fixation phase — (i) Formation of G3P
B. Reduction phase — (ii) CO₂ combines with RUBP
C. Regeneration phase — (iii) RUBP regenerated
1. A-(ii), B-(i), C-(iii)
2. A-(i), B-(iii), C-(ii)
3. A-(iii), B-(ii), C-(i)
4. A-(ii), B-(iii), C-(i)

Explanation: The correct match is option 1. In the fixation phase, CO₂ reacts with RUBP to form 3-PGA. The reduction phase involves ATP and NADPH reducing 3-PGA to G3P. Finally, in the regeneration phase, some G3P molecules regenerate RUBP, enabling the cycle to continue fixing new CO₂ molecules.

6. The Calvin cycle was discovered by:
1. Melvin Calvin
2. F.F. Blackman
3. C.B. van Niel
4. Jan Ingenhousz

Explanation: The Calvin cycle was discovered by Melvin Calvin and his colleagues in 1957 using radioactive carbon (¹⁴C). They traced the path of carbon dioxide in photosynthesis and elucidated the sequence of reactions converting CO₂ to sugars. Calvin received the Nobel Prize in Chemistry in 1961 for this discovery.

7. Fill in the Blank:
Each turn of the Calvin cycle fixes _______ molecule of CO₂.
1. One
2. Two
3. Three
4. Six

Explanation: Each turn of the Calvin cycle fixes one molecule of CO₂. To produce one molecule of glucose (C₆H₁₂O₆), the cycle must turn six times, consuming 18 ATP and 12 NADPH molecules. This ensures sufficient carbon assimilation to form a complete hexose sugar molecule during photosynthesis.

8. The main purpose of ATP and NADPH in the Calvin cycle is:
1. Energy and reducing power for CO₂ fixation
2. Synthesis of oxygen
3. Absorption of light
4. Breakdown of water

Explanation: ATP provides energy while NADPH supplies reducing power to convert 3-phosphoglycerate into glyceraldehyde-3-phosphate. These molecules are generated during the light-dependent reactions and utilized in the stroma. Without ATP and NADPH, carbon fixation cannot proceed, and carbohydrate synthesis would be impossible in plants.

9. Choose the Correct Statements (Statement I & Statement II):
Statement I: The Calvin cycle occurs only during the day.
Statement II: It depends on ATP and NADPH produced in light reactions.
1. Both statements are true.
2. Statement I true, II false.
3. Statement I false, II true.
4. Both statements false.

Explanation: The correct answer is option 1. Though the Calvin cycle reactions do not directly require light, they occur only during the day because they depend on ATP and NADPH generated in light reactions. Hence, both statements are true, and the Calvin cycle remains functionally light-dependent.

10. Which molecule is regenerated at the end of the Calvin cycle?
1. 3-Phosphoglycerate
2. Glyceraldehyde-3-phosphate
3. Ribulose-1,5-bisphosphate
4. Glucose

Explanation: The correct answer is Ribulose-1,5-bisphosphate (RUBP). After CO₂ fixation and reduction phases, part of the G3P produced is used to regenerate RUBP. This regeneration ensures the cycle continues by providing fresh RUBP molecules for new CO₂ fixation, maintaining the cyclic nature of photosynthetic carbon assimilation.

Topic: Photosynthetic Pathways; Subtopic: C3, C4, and CAM Cycles

Keyword Definitions:

• C4 Pathway: A photosynthetic process where the first stable compound is a four-carbon compound (oxaloacetate). It occurs in plants like maize and sugarcane.

• Calvin Cycle: The dark phase of photosynthesis responsible for carbon fixation using ATP and NADPH produced in the light reaction.

• Photorespiration: A process where RuBisCO fixes oxygen instead of CO2, leading to the formation of phosphoglycolate and loss of carbon and energy.

• Light Reaction: The photochemical phase where light energy is converted into chemical energy as ATP and NADPH, releasing O2.

• RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme responsible for CO2 fixation in the Calvin cycle and oxygenation in photorespiration.

Lead Question – 2024 (Jhajjar)
Match List-I with List-II
List-I | List-II
A. C4 Pathway — I.
B. Light reaction — II. Ribulose 1,5-bisphosphate
C. Photorespiration — III. Phosphoenol Pyruvate
D. Calvin cycle — IV. Phosphoglycolate

1. A-II, B-I, C-IV, D-III
2. A-IV, B-II, C-I, D-III
3. A-III, B-I, C-IV, D-II
4. A-III, B-IV, C-II, D-I

Explanation: The correct answer is A–III, B–I, C–IV, D–II. The C4 pathway begins with phosphoenol pyruvate (PEP) forming oxaloacetate. The light reaction involves photophosphorylation producing ATP and NADPH. Photorespiration produces phosphoglycolate as a by-product, while the Calvin cycle uses ribulose 1,5-bisphosphate (RuBP) for CO2 fixation. Each step links specific enzymes and substrates for efficient photosynthesis.

1. The primary CO2 acceptor in the C4 pathway is:
1. Ribulose 1,5-bisphosphate
2. 3-phosphoglycerate
3. Phosphoenol Pyruvate
4. Pyruvic acid

Explanation: The correct answer is Phosphoenol Pyruvate (PEP). In C4 plants like maize, CO2 is first fixed by PEP carboxylase in mesophyll cells forming oxaloacetate. This step increases efficiency under high light and low CO2 conditions by minimizing photorespiration and concentrating CO2 around RuBisCO in bundle sheath cells.

2. The enzyme responsible for carbon fixation in the Calvin cycle is:
1. PEP carboxylase
2. RuBisCO
3. NADP reductase
4. ATP synthase

Explanation: The correct answer is RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase). It catalyzes the first step of the Calvin cycle by combining CO2 with RuBP to form 3-phosphoglycerate. Despite being the most abundant enzyme, it also catalyzes oxygen fixation during photorespiration, reducing photosynthetic efficiency under high temperature and low CO2 levels.

3. The first stable product of the Calvin cycle is:
1. 3-phosphoglycerate
2. Oxaloacetate
3. Malate
4. Pyruvate

Explanation: The correct answer is 3-phosphoglycerate (3-PGA). It is formed when CO2 combines with RuBP, catalyzed by RuBisCO in the Calvin cycle. 3-PGA is subsequently reduced using ATP and NADPH to form triose phosphates, which contribute to carbohydrate synthesis. This pathway is typical in C3 plants like wheat and rice.

4. Which of the following occurs only during the light reaction of photosynthesis?
1. Carbon fixation
2. Oxygen evolution
3. Formation of phosphoglycolate
4. Synthesis of glucose

Explanation: The correct answer is Oxygen evolution. During the light reaction, photolysis of water occurs in the presence of light and chlorophyll within photosystem II. This releases O2, electrons, and protons, which are used to generate ATP and NADPH. These energy molecules are later utilized in the Calvin cycle for CO2 fixation.

5. Which of the following is formed during photorespiration?
1. 3-phosphoglycerate
2. Phosphoglycolate
3. Oxaloacetate
4. Ribulose monophosphate

Explanation: The correct answer is Phosphoglycolate. During photorespiration, RuBisCO fixes O2 instead of CO2, leading to the formation of phosphoglycolate and 3-phosphoglycerate. Phosphoglycolate is toxic and must be metabolized, causing loss of ATP and CO2. Hence, photorespiration reduces photosynthetic efficiency in C3 plants under stress conditions.

6. Which one is common to both light reaction and Calvin cycle?
1. Use of ATP
2. Formation of NADPH
3. Evolution of oxygen
4. Absorption of light energy

Explanation: The correct answer is Use of ATP. ATP is produced during the light reaction through photophosphorylation and utilized in the Calvin cycle for converting 3-phosphoglycerate to triose phosphate. This energy transfer connects both phases of photosynthesis, ensuring continuous carbohydrate synthesis from CO2 and water.

7. Assertion–Reason Type Question:
Assertion (A): C4 plants show higher photosynthetic efficiency than C3 plants.
Reason (R): C4 plants minimize photorespiration by concentrating CO2 around RuBisCO.
1. Both A and R are true, and R is the correct explanation of A.
2. Both A and R are true, but R is not the correct explanation of A.
3. A is true but R is false.
4. A is false but R is true.

Explanation: The correct answer is Both A and R are true, and R is the correct explanation of A. C4 plants like maize possess Kranz anatomy where CO2 is fixed in mesophyll cells and concentrated in bundle sheath cells, reducing RuBisCO oxygenase activity. This adaptation enhances efficiency and minimizes photorespiratory losses.

8. Matching Type Question:
Match the following enzymes with their functions:
A. RuBisCO — (i) Fixation of CO2 in Calvin cycle
B. PEP carboxylase — (ii) Fixation of CO2 in C4 pathway
C. ATP synthase — (iii) ATP formation
D. NADP reductase — (iv) Formation of NADPH

1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–ii, C–iv, D–i
4. A–iv, B–iii, C–ii, D–i

Explanation: The correct answer is A–i, B–ii, C–iii, D–iv. RuBisCO fixes CO2 in Calvin cycle, PEP carboxylase in the C4 pathway, ATP synthase produces ATP during photophosphorylation, and NADP reductase generates NADPH at the end of light reaction. These enzymes coordinate to sustain photosynthetic energy flow.

9. Fill in the Blank / Completion Type Question:
In C4 plants, CO2 fixation occurs in __________ cells.
1. Bundle sheath
2. Palisade
3. Mesophyll
4. Guard

Explanation: The correct answer is Mesophyll cells. In C4 plants, the initial CO2 fixation by PEP carboxylase occurs in mesophyll cells, forming oxaloacetate. This is later transported to bundle sheath cells, where CO2 is released for the Calvin cycle. This two-step process reduces photorespiration and enhances photosynthetic efficiency.

10. Choose the Correct Statements Type Question:
Statement I: Photorespiration occurs when RuBisCO binds O2 instead of CO2.
Statement II: It results in ATP and sugar production.
1. Both statements are correct.
2. Both statements are incorrect.
3. Only Statement I is correct.
4. Only Statement II is correct.

Explanation: The correct answer is Only Statement I is correct. During photorespiration, RuBisCO’s oxygenase activity forms phosphoglycolate and 3-PGA, leading to CO2 loss and ATP consumption rather than production. Therefore, photorespiration is a wasteful process that reduces photosynthetic efficiency in plants under hot and dry conditions.

Topic: Light Reaction (Photochemical Phase); Subtopic: Formation of ATP and NADPH during Light-Dependent Reaction

Keyword Definitions:
• Photochemical Phase: The light-dependent stage of photosynthesis where sunlight energy is converted into chemical energy as ATP and NADPH.
• Photolysis: Splitting of water using light energy, releasing O2, protons, and electrons.
• NADPH: An energy-rich molecule formed during light reactions, used in the dark phase for CO2 fixation.
• ATP: The primary energy currency of the cell, synthesized by photophosphorylation.
• Carboxylation: The fixation of CO2 into organic compounds during the dark reaction.

Lead Question – 2024 (Jhajjhar)
The photochemical phase of photosynthesis include:
A. Oxygen release
B. Formation of NADPH
C. Use of ATP
D. Water splitting
E. Carboxylation
1. C and E only
2. A, B and D only
3. B, C and E only
4. A, B, C and D only

Explanation: The correct answer is A, B and D only. The photochemical phase or light reaction of photosynthesis occurs in the thylakoid membranes. It involves photolysis of water releasing oxygen, formation of ATP and NADPH. The use of ATP and carboxylation occur in the dark reaction during CO2 fixation in the Calvin cycle.

1. The light-dependent reactions of photosynthesis occur in:
1. Stroma
2. Thylakoid membrane
3. Cytoplasm
4. Outer chloroplast membrane

Explanation: The correct answer is thylakoid membrane. The thylakoids of chloroplasts contain chlorophyll pigments that capture solar energy to drive photochemical reactions, leading to ATP synthesis and NADPH formation. These products are essential for the light-independent (dark) phase occurring in the stroma.

2. During photolysis of water, which of the following is released?
1. CO2
2. O2
3. Glucose
4. NADPH

Explanation: The correct answer is O2. In the light reaction, water molecules split under the influence of sunlight and photosystem II into protons, electrons, and molecular oxygen. This process replenishes the electrons lost by chlorophyll, and oxygen diffuses out as a by-product of photosynthesis.

3. The primary electron acceptor in Photosystem II is:
1. P700
2. Ferredoxin
3. Plastoquinone
4. NADP+

Explanation: The correct answer is Plastoquinone. After the excitation of chlorophyll molecule P680 in Photosystem II, the excited electrons are transferred to plastoquinone. It then transports electrons through the electron transport chain, leading to ATP formation via chemiosmosis.

4. Which process directly depends on light energy?
1. Photophosphorylation
2. Carbon fixation
3. Glycolysis
4. Krebs cycle

Explanation: The correct answer is photophosphorylation. This is the process of forming ATP from ADP and inorganic phosphate using light energy during photosynthesis. It occurs within the thylakoid membranes, driving both cyclic and non-cyclic pathways of electron transport.

5. The dark reaction of photosynthesis is also known as:
1. Light reaction
2. Calvin cycle
3. Hill reaction
4. Photorespiration

Explanation: The correct answer is Calvin cycle. The dark reaction or biosynthetic phase uses ATP and NADPH produced in the light phase to fix CO2 into carbohydrates. It occurs in the stroma of chloroplasts, independent of direct light energy.

6. The overall function of light reaction is to:
1. Produce ATP and NADPH
2. Produce CO2
3. Reduce glucose
4. Release energy as heat

Explanation: The correct answer is produce ATP and NADPH. The light reaction converts solar energy into chemical energy stored in ATP and NADPH molecules. These compounds provide the necessary energy and reducing power for carbon assimilation in the dark phase.

7. Assertion-Reason Question:
Assertion (A): Oxygen is evolved during the photochemical phase of photosynthesis.
Reason (R): Water is split by light energy into hydrogen and oxygen during photolysis.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true, but R is false
4. A is false, but R is true

Explanation: Both Assertion and Reason are true, and R correctly explains A. During photolysis of water in the light phase, solar energy splits water molecules to release O2. The oxygen diffuses out of the chloroplast, while the hydrogen and electrons are used in NADPH and ATP formation.

8. Matching Type Question:
Match the following components of photosynthesis with their respective functions:

A. Photosystem I — (i) Splitting of water
B. Photosystem II — (ii) Formation of NADPH
C. ATP synthase — (iii) ATP formation
D. NADP+ — (iv) Electron acceptor

1. A-(ii), B-(i), C-(iii), D-(iv)
2. A-(i), B-(iv), C-(ii), D-(iii)
3. A-(iii), B-(i), C-(iv), D-(ii)
4. A-(iv), B-(ii), C-(i), D-(iii)

Explanation: The correct match is A-(ii), B-(i), C-(iii), D-(iv). Photosystem II initiates photolysis of water, Photosystem I reduces NADP+ to NADPH, ATP synthase synthesizes ATP, and NADP+ acts as the final electron acceptor in the light reaction.

9. Fill in the Blank Question:
During the photochemical phase, ATP is formed by the process of __________.
1. Photolysis
2. Photophosphorylation
3. Glycolysis
4. Photorespiration

Explanation: The correct answer is photophosphorylation. This process involves the synthesis of ATP using light energy through electron transport across thylakoid membranes. It occurs in two forms: cyclic and non-cyclic, providing energy required for carbon fixation in the subsequent phase.

10. Choose the Correct Statements Question:
Statement I: Light reactions supply ATP and NADPH to the dark reactions.
Statement II: Carboxylation occurs during the photochemical phase.
1. Both statements are correct
2. Only Statement I is correct
3. Only Statement II is correct
4. Both are incorrect

Explanation: The correct answer is Only Statement I is correct. The light-dependent phase produces ATP and NADPH, which power the dark phase of photosynthesis. Carboxylation, however, occurs in the dark reaction where CO2 is fixed into organic molecules using these energy carriers.

Topic: Photorespiration and C4 Pathway; Subtopic: C3 and C4 Plants

Keyword Definitions:

• C3 Plants: Plants in which CO2 fixation occurs directly via the Calvin cycle in mesophyll cells, producing 3-carbon compounds.

• C4 Plants: Plants in which CO2 is first fixed into 4-carbon compounds in mesophyll cells and then transported to bundle sheath cells for the Calvin cycle.

• Photorespiration: Process in C3 plants where RuBisCO binds O2 instead of CO2, reducing carbon fixation efficiency.

• RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, the enzyme that catalyzes CO2 fixation in the Calvin cycle.

• Bundle Sheath Cells: Specialized cells in C4 plants where the Calvin cycle occurs with minimal photorespiration.

Lead Question – 2024

Given below are two statements:
Statement I: In C3 plants, some O2 binds to RuBisCO, hence CO2 fixation is decreased.
Statement II: In C4 plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration.
In the light of the above statements, choose the correct answer from the options given below:

(1) Both statement I and Statement II are false
(2) Statement I is true but Statement II is false
(3) Statement I is false but Statement II is true
(4) Both Statement I and Statement II are true

Explanation:

Statement I is correct because in C3 plants, RuBisCO can catalyze the reaction with O2 instead of CO2, leading to photorespiration and reduced CO2 fixation. Statement II is also correct as C4 plants have spatial separation of initial CO2 fixation in mesophyll cells and Calvin cycle in bundle sheath cells, resulting in minimal photorespiration. The CO2 concentrating mechanism in C4 plants ensures that bundle sheath cells operate efficiently without oxygen interference. Therefore, both statements are true, making option (4) Both Statement I and Statement II are true the correct choice.

1. Single Correct Answer

Which enzyme in C3 plants is responsible for photorespiration?

(1) ATP synthase
(2) RuBisCO
(3) PEP carboxylase
(4) NADP reductase

Explanation: RuBisCO catalyzes CO2 fixation in C3 plants but also binds O2, causing photorespiration. This reduces the net carbon gain. Option (2) RuBisCO is correct.

2. Single Correct Answer

In C4 plants, CO2 is first fixed in:

(1) Bundle sheath cells
(2) Chloroplast of mesophyll cells
(3) Cytoplasm of guard cells
(4) Stomatal cavity

Explanation: In C4 plants, CO2 is initially fixed by PEP carboxylase in the chloroplasts of mesophyll cells, forming 4-carbon compounds transported to bundle sheath cells for the Calvin cycle. Option (2) Chloroplast of mesophyll cells is correct.

3. Single Correct Answer

Photorespiration reduces efficiency of photosynthesis because:

(1) ATP is synthesized excessively
(2) Oxygen is converted to CO2
(3) CO2 fixation decreases and energy is wasted
(4) Chlorophyll is degraded

Explanation: Photorespiration occurs when RuBisCO fixes O2 instead of CO2, leading to release of CO2 and consumption of ATP without sugar production, lowering photosynthetic efficiency. Option (3) CO2 fixation decreases and energy is wasted is correct.

4. Single Correct Answer

Which cells of C4 plants are specialized for Calvin cycle?

(1) Mesophyll cells
(2) Bundle sheath cells
(3) Guard cells
(4) Epidermal cells

Explanation: Bundle sheath cells in C4 plants contain chloroplasts with high CO2 concentration due to transported 4-carbon compounds, allowing the Calvin cycle to proceed efficiently with minimal photorespiration. Option (2) Bundle sheath cells is correct.

5. Assertion–Reason Question

Assertion (A): C4 plants exhibit lower photorespiration than C3 plants.
Reason (R): CO2 is concentrated in bundle sheath cells by a biochemical pump.

Explanation: Both Assertion and Reason are true. The C4 pathway pumps CO2 from mesophyll to bundle sheath cells, increasing CO2:O2 ratio and suppressing RuBisCO oxygenase activity. Correct answer: Both A and R are true, R explains A.

6. Matching Type Question

Match the plant type with its characteristic:
A. C3 – I. High photorespiration
B. C4 – II. Low photorespiration
C. CAM – III. Temporal separation of CO2 fixation
D. Aquatic plant – IV. Minimal O2 interference

(1) A–I, B–II, C–III, D–IV
(2) A–II, B–I, C–IV, D–III
(3) A–III, B–IV, C–I, D–II
(4) A–IV, B–III, C–II, D–I

Explanation: C3 plants show high photorespiration, C4 plants suppress it via CO2 pump, CAM plants separate CO2 fixation temporally, and some aquatic plants have minimal O2 interference. Correct option: (1) A–I, B–II, C–III, D–IV.

7. Fill in the Blanks Question

In C4 plants, ______ cells perform initial CO2 fixation and ______ cells perform the Calvin cycle.

(1) Bundle sheath, mesophyll
(2) Mesophyll, bundle sheath
(3) Guard, mesophyll
(4) Epidermal, bundle sheath

Explanation: In C4 plants, mesophyll cells fix CO2 into 4-carbon compounds using PEP carboxylase, and bundle sheath cells perform the Calvin cycle. Correct option: (2) Mesophyll, bundle sheath.

8. Single Correct Answer

Which enzyme fixes CO2 in C4 mesophyll cells?

(1) RuBisCO
(2) PEP carboxylase
(3) NADP reductase
(4) ATP synthase

Explanation: PEP carboxylase in mesophyll cells of C4 plants initially fixes CO2 into oxaloacetate, a 4-carbon compound, preventing RuBisCO oxygenase activity. Correct option: (2) PEP carboxylase.

9. Single Correct Answer

Why do C4 plants have higher photosynthetic efficiency in hot climates?

(1) RuBisCO is absent
(2) CO2 concentration in bundle sheath cells reduces photorespiration
(3) They do not need sunlight
(4) Water absorption is higher

Explanation: In C4 plants, CO2 is concentrated in bundle sheath cells, reducing oxygenation by RuBisCO, lowering photorespiration, and increasing photosynthetic efficiency in hot climates. Correct option: (2) CO2 concentration in bundle sheath cells reduces photorespiration.

10. Choose the Correct Statements (Statement I & II)

Statement I: C3 plants are more affected by oxygen concentration than C4 plants.
Statement II: C4 plants utilize ATP to concentrate CO2 around RuBisCO.

(1) Both Statement I and II are false
(2) Statement I is true, Statement II is false
(3) Statement I is false, Statement II is true
(4) Both Statement I and II are true

Explanation: C3 plants are prone to photorespiration, affected by O2 concentration. C4 plants expend ATP to pump CO2 into bundle sheath cells, reducing oxygenase activity of RuBisCO. Both statements are correct. Correct option: (4) Both Statement I and II are true.

Subtopic: Calvin Cycle

Keyword Definitions:

• Calvin Cycle: A biochemical pathway in chloroplasts that fixes CO2 into carbohydrates using ATP and NADPH.

• ATP: Adenosine triphosphate, a molecule that stores and transfers energy within cells.

• NADPH: Nicotinamide adenine dinucleotide phosphate, an electron carrier providing reducing power for biosynthetic reactions.

• CO2 fixation: The incorporation of carbon dioxide into organic molecules during photosynthesis.

• Ribulose-1,5-bisphosphate (RuBP): The CO2 acceptor molecule in the Calvin cycle.

• Light Reaction: The photosynthetic process generating ATP and NADPH.

• Dark Reaction: The Calvin cycle reactions that do not directly require light but use ATP and NADPH.

Lead Question – 2024

How many molecules of ATP and NADPH are required for every molecule of CO2 fixed in the Calvin cycle?

(1) 2 molecules of ATP and 2 molecules of NADPH
(2) 3 molecules of ATP and 3 molecules of NADPH
(3) 3 molecules of ATP and 2 molecules of NADPH
(4) 2 molecules of ATP and 3 molecules of NADPH

Explanation: In the Calvin cycle, each CO2 fixed requires 3 molecules of ATP to provide energy for the regeneration of RuBP and the synthesis of 3-phosphoglycerate, and 2 molecules of NADPH to supply electrons for the reduction of 3-phosphoglycerate to glyceraldehyde-3-phosphate. These stoichiometric requirements are essential for understanding photosynthetic efficiency and the energy cost of carbon fixation. ATP serves as the energy source, while NADPH provides the reducing power, both generated in the light reactions. Accurate knowledge of these numbers is fundamental in plant biochemistry. (Answer: 3)

1. Single Correct Answer:
Which molecule acts as the primary CO2 acceptor in the Calvin cycle?
(1) ATP
(2) NADPH
(3) RuBP
(4) G3P

Explanation: Ribulose-1,5-bisphosphate (RuBP) is the primary CO2 acceptor in the Calvin cycle. It reacts with CO2 catalyzed by RuBisCO to form 3-phosphoglycerate. ATP provides energy and NADPH provides reducing power, but they are not CO2 acceptors. Understanding RuBP’s role is essential for studying carbon fixation. (Answer: 3)

2. Single Correct Answer:
Which molecule provides reducing power for converting 3-phosphoglycerate to glyceraldehyde-3-phosphate?
(1) ATP
(2) NADPH
(3) CO2
(4) RuBP

Explanation: NADPH provides the reducing equivalents for converting 3-phosphoglycerate to glyceraldehyde-3-phosphate in the Calvin cycle. ATP provides energy but not electrons. Correct identification of NADPH's role is critical for understanding the energy and electron requirements in carbon fixation. (Answer: 2)

3. Single Correct Answer:
The energy for the regeneration of RuBP in Calvin cycle comes from:
(1) NADPH
(2) CO2
(3) ATP
(4) G3P

Explanation: ATP provides energy for the regeneration of RuBP from glyceraldehyde-3-phosphate, ensuring the cycle continues. NADPH is used for reduction, while CO2 is the substrate. Understanding ATP's role clarifies energy allocation during carbon fixation. (Answer: 3)

4. Single Correct Answer:
Which reaction in the Calvin cycle is independent of light but requires ATP and NADPH?
(1) Light reaction
(2) Dark reaction
(3) Photorespiration
(4) Photolysis

Explanation: Dark reactions of the Calvin cycle do not require light directly but use ATP and NADPH from light reactions to fix CO2 and synthesize sugars. Light reactions generate ATP and NADPH. Understanding this separation is fundamental to plant physiology. (Answer: 2)

5. Single Correct Answer:
For synthesizing one molecule of G3P in Calvin cycle, how many molecules of CO2 are required?
(1) 1
(2) 2
(3) 3
(4) 6

Explanation: To produce one molecule of glyceraldehyde-3-phosphate (G3P), three molecules of CO2 are fixed in the Calvin cycle. This ensures sufficient carbon atoms for sugar synthesis. Each CO2 consumes 3 ATP and 2 NADPH. Correct stoichiometry is crucial for modeling photosynthetic output. (Answer: 3)

6. Assertion-Reason:
Assertion (A): Calvin cycle consumes ATP and NADPH for CO2 fixation.
Reason (R): ATP provides energy and NADPH provides electrons for reduction reactions.
(1) Both A and R are true, R explains A
(2) Both A and R are true, R does not explain A
(3) A true, R false
(4) A false, R true

Explanation: The Calvin cycle requires ATP for energy and NADPH for reducing power during CO2 fixation. Both the assertion and reason are true, and the reason correctly explains why the cycle consumes these molecules. Understanding this relationship is key in photosynthetic energy budgeting. (Answer: 1)

7. Matching Type:
Match List I (Molecule) with List II (Role in Calvin cycle):
A. ATP – (i) Reducing power
B. NADPH – (ii) Energy supply
C. CO2 – (iii) Carbon source
Options:
(1) A-ii, B-i, C-iii
(2) A-i, B-ii, C-iii
(3) A-iii, B-ii, C-i
(4) A-ii, B-iii, C-i

Explanation: ATP supplies energy, NADPH provides electrons for reduction, and CO2 serves as the carbon source. Correct matching is fundamental for understanding Calvin cycle energetics and carbon fixation. (Answer: 1)

8. Fill in the Blanks:
For every molecule of CO2 fixed in Calvin cycle, __________ molecules of ATP and __________ molecules of NADPH are required.
(1) 2, 2
(2) 3, 3
(3) 3, 2
(4) 2, 3

Explanation: Each CO2 fixed consumes 3 molecules of ATP for energy and 2 molecules of NADPH for reducing power. This stoichiometry is crucial for calculating the energy cost of carbon fixation in plants. (Answer: 3)

9. Single Correct Answer:
The primary site of Calvin cycle in plant cells is:
(1) Mitochondria
(2) Stroma of chloroplast
(3) Cytoplasm
(4) Thylakoid lumen

Explanation: The Calvin cycle occurs in the stroma of chloroplasts where enzymes, ATP, and NADPH are available for CO2 fixation. Light reactions occur in thylakoids, providing the energy and reducing equivalents needed. (Answer: 2)

10. Choose Correct Statements:
Statement I: NADPH is consumed in the Calvin cycle for reduction.
Statement II: ATP is used for phosphorylation reactions in the Calvin cycle.
Options:
(1) Both statements are true
(2) Statement I true, Statement II false
(3) Statement I false, Statement II true
(4) Both statements are false

Explanation: Both statements correctly describe the Calvin cycle. NADPH provides electrons for reduction of 3-phosphoglycerate, and ATP provides energy for phosphorylation steps and RuBP regeneration. Understanding these statements clarifies the energy and electron flow in photosynthesis. (Answer: 1)

Topic: Mechanism of Photosynthesis; Subtopic: Dark Reaction or Biosynthetic Phase

Keyword Definitions:

• Photosynthesis: The process by which green plants synthesize glucose using sunlight, CO2, and water.

• Dark Reaction: The light-independent phase of photosynthesis in which ATP and NADPH are used to fix CO2 into glucose.

• ATP (Adenosine Triphosphate): The energy currency molecule that powers biochemical reactions in cells.

• NADPH: A reducing agent that donates hydrogen for the synthesis of carbohydrates in the Calvin cycle.

• CO2 Fixation: The conversion of carbon dioxide into organic compounds during photosynthesis.

Lead Question - 2024
Which of the following are required for the dark reaction of photosynthesis?
A. Light
B. Chlorophyll
C. CO2
D. ATP
E. NADPH
Choose the correct answer from the options given below:
(1) B, C and D only
(2) C, D and E only
(3) D and E only
(4) A, B and C only

Explanation: The dark reaction, or Calvin cycle, does not directly require light or chlorophyll but uses ATP and NADPH produced during the light reaction to fix CO2 into glucose. It occurs in the stroma of chloroplasts through carboxylation, reduction, and regeneration phases. Thus, the correct answer is (2) C, D and E only.

Guessed Questions:

1. In which part of the chloroplast does the dark reaction occur?
(1) Grana
(2) Thylakoid membrane
(3) Stroma
(4) Intermembrane space

Explanation: The dark reaction of photosynthesis occurs in the stroma of chloroplasts, where enzymes required for the Calvin cycle are present. It involves ATP and NADPH utilization for CO2 fixation to form glucose. The stroma provides the ideal environment for enzymatic reactions. Answer: (3) Stroma.

2. Which compound is the primary acceptor of CO2 in the Calvin cycle?
(1) RuBP
(2) PGA
(3) PEP
(4) Glucose

Explanation: Ribulose-1,5-bisphosphate (RuBP) acts as the primary CO2 acceptor in the Calvin cycle. It combines with CO2 to form two molecules of 3-phosphoglyceric acid (PGA) in a reaction catalyzed by Rubisco enzyme. This step initiates the dark reaction. Answer: (1) RuBP.

3. The first stable product of the Calvin cycle is:
(1) Glucose
(2) PGA (3-Phosphoglyceric acid)
(3) RuBP
(4) G3P

Explanation: The first stable product of the Calvin cycle is 3-phosphoglyceric acid (PGA), a three-carbon compound formed when CO2 reacts with RuBP. PGA is later reduced to glyceraldehyde-3-phosphate using ATP and NADPH. Answer: (2) PGA.

4. Which enzyme catalyzes the first step of the Calvin cycle?
(1) Rubisco
(2) PEP carboxylase
(3) ATP synthase
(4) NADP reductase

Explanation: Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) catalyzes the carboxylation of RuBP with CO2 to form PGA. It is the most abundant enzyme in the world and plays a key role in carbon fixation during the Calvin cycle. Answer: (1) Rubisco.

5. Assertion-Reason Type Question
Assertion (A): The dark reaction can occur in light as well.
Reason (R): It depends on ATP and NADPH produced during the light reaction.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation: The dark reaction can occur in the presence of light as it requires ATP and NADPH generated by the light reaction. Although termed “dark,” it is light-independent, not light-avoiding. Answer: (1).

6. Which of the following is not required for the Calvin cycle?
(1) ATP
(2) NADPH
(3) Oxygen
(4) CO2

Explanation: Oxygen is not required for the Calvin cycle. This phase involves ATP and NADPH utilization to reduce CO2 and form glucose. Oxygen is produced during the light reaction, not used in the dark reaction. Answer: (3) Oxygen.

7. Matching Type Question
A. ATP → I. Provides energy
B. NADPH → II. Provides reducing power
C. Rubisco → III. Fixes CO2
D. Stroma → IV. Site of dark reaction
(1) A-I, B-II, C-III, D-IV
(2) A-II, B-I, C-III, D-IV
(3) A-I, B-III, C-II, D-IV
(4) A-III, B-II, C-I, D-IV

Explanation: In photosynthesis, ATP provides energy, NADPH supplies reducing power, Rubisco fixes CO2, and stroma is the site where dark reactions occur. These together convert CO2 into sugars. Answer: (1) A-I, B-II, C-III, D-IV.

8. Fill in the Blanks
The enzyme that catalyzes the fixation of CO2 in the Calvin cycle is ________.
(1) ATP synthase
(2) Rubisco
(3) NADP reductase
(4) PEP carboxylase

Explanation: Rubisco, the most abundant enzyme on Earth, catalyzes the fixation of carbon dioxide with RuBP in the first step of the Calvin cycle. It is essential for converting inorganic carbon into organic molecules. Answer: (2) Rubisco.

9. Choose the Correct Statements (Statement I & II)
Statement I: The dark reaction requires products of the light reaction.
Statement II: It occurs only during darkness.
(1) Both statements are true
(2) Statement I true, II false
(3) Statement I false, II true
(4) Both statements are false

Explanation: The dark reaction depends on ATP and NADPH generated during the light reaction but can proceed in light or darkness, as it does not directly need light. Therefore, Statement I is true, and II is false. Answer: (2) Statement I true, II false.

10. In which phase of the Calvin cycle is RuBP regenerated?
(1) Carboxylation
(2) Reduction
(3) Regeneration
(4) Glycolysis

Explanation: The regeneration phase of the Calvin cycle reforms RuBP from glyceraldehyde-3-phosphate using ATP, allowing the cycle to continue fixing CO2. It ensures the cyclic nature of photosynthetic carbon fixation. Answer: (3) Regeneration.

Topic: Light Reactions of Photosynthesis; Subtopic: Photophosphorylation and Photosystems

Keyword Definitions:

• Photosystem I (PS I): A pigment system absorbing light at 700 nm, responsible for NADPH formation.

• Photosystem II (PS II): A pigment system absorbing light at 680 nm, initiating photolysis of water.

• Grana Lamellae: Stacked thylakoid membranes in chloroplasts containing PS I and PS II.

• Stroma Lamellae: Unstacked thylakoid membranes connecting grana, containing only PS I.

• Photophosphorylation: ATP synthesis using light energy during photosynthesis.

• Cyclic Photophosphorylation: Process where only PS I is involved and no NADPH is produced.

• Non-Cyclic Photophosphorylation: Both PS I and PS II are involved, forming ATP and NADPH + H⁺.

Lead Question - 2023 (Manipur)

Which out of the following statements is incorrect?
1. Grana lamellae have both PS I and PS II
2. Cyclic photophosphorylation involved both PS I and PS II
3. Both ATP and NADPH + H⁺ are synthesised during non-cyclic photophosphorylation
4. Stroma lamellae lack PS II and NAP reductase

Explanation:
Cyclic photophosphorylation involves only PS I and not PS II. Therefore, statement 2 is incorrect. In non-cyclic photophosphorylation, both ATP and NADPH + H⁺ are formed using PS I and PS II. Grana lamellae possess both photosystems, while stroma lamellae have only PS I. Hence, the incorrect statement is option 2.

Guessed Questions:

1. Single Correct Answer Type:
Which photosystem is responsible for the photolysis of water?
1. PS I
2. PS II
3. Both PS I and PS II
4. None of these
Explanation:
PS II (P680) is responsible for the photolysis of water into oxygen, protons, and electrons. It absorbs light at 680 nm and releases electrons that travel through the electron transport chain to PS I. Hence, the correct answer is PS II.

2. Single Correct Answer Type:
Which component of the chloroplast connects the grana stacks?
1. Grana lamellae
2. Stroma lamellae
3. Matrix lamellae
4. Thylakoid lumen
Explanation:
Stroma lamellae act as bridges between grana stacks. They contain only PS I and facilitate cyclic photophosphorylation. These lamellae ensure continuous transfer of energy during light-dependent reactions. Thus, the correct answer is stroma lamellae.

3. Single Correct Answer Type:
During non-cyclic photophosphorylation, electrons are finally accepted by:
1. ATP
2. NADP⁺
3. Oxygen
4. Cytochrome complex
Explanation:
In non-cyclic photophosphorylation, electrons from PS I are transferred to NADP⁺, forming NADPH + H⁺. This process links light absorption to the reduction of NADP⁺. Therefore, the final electron acceptor is NADP⁺.

4. Single Correct Answer Type:
Which event does not occur during cyclic photophosphorylation?
1. Electron returns to PS I
2. NADPH formation
3. ATP synthesis
4. Light absorption by PS I
Explanation:
Cyclic photophosphorylation involves only PS I and results in ATP production. NADPH formation does not occur as electrons return to PS I after moving through the electron transport chain. Hence, NADPH formation is absent. Correct answer: option 2.

5. Single Correct Answer Type:
In which region of the chloroplast do light reactions occur?
1. Matrix
2. Stroma
3. Thylakoid membrane
4. Outer membrane
Explanation:
Light reactions of photosynthesis occur in the thylakoid membranes of chloroplasts, where photosystems, electron carriers, and ATP synthase are located. This is the site for ATP and NADPH formation. Thus, the correct answer is thylakoid membrane.

6. Single Correct Answer Type:
Which of the following statements is true about PS I and PS II?
1. PS I operates at 700 nm and PS II at 680 nm
2. PS I and PS II both operate at 700 nm
3. PS II operates at 700 nm
4. Both operate at 680 nm
Explanation:
PS I has a reaction center at P700 and absorbs light at 700 nm, while PS II has a reaction center at P680 absorbing at 680 nm. This difference allows sequential electron transfer between photosystems. Correct answer: option 1.

7. Assertion-Reason Type:
Assertion (A): Non-cyclic photophosphorylation involves both PS I and PS II.
Reason (R): It produces both ATP and NADPH + H⁺.
1. Both A and R are true and R is the correct explanation of A
2. Both A and R are true but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Explanation:
Both statements are true and R correctly explains A. In non-cyclic photophosphorylation, both photosystems work together to produce ATP and NADPH + H⁺ simultaneously. Thus, the correct answer is option 1.

8. Matching Type:
Match the following:
A. PS I — 1. P680
B. PS II — 2. P700
C. Photolysis site — 3. Thylakoid membrane
D. ATP formation — 4. ATP synthase complex

1. A-2, B-1, C-3, D-4
2. A-1, B-2, C-4, D-3
3. A-2, B-3, C-1, D-4
4. A-3, B-4, C-2, D-1
Explanation:
PS I corresponds to P700, PS II to P680, photolysis occurs in the thylakoid membrane, and ATP forms at the ATP synthase complex. Thus, the correct matching is A-2, B-1, C-3, D-4.

9. Fill in the Blanks:
In cyclic photophosphorylation, only ______ is involved.
1. PS I
2. PS II
3. Both PS I and PS II
4. None
Explanation:
Cyclic photophosphorylation involves only PS I. Electrons move in a cyclic path and return to PS I after energy transfer through electron carriers, generating ATP but no NADPH. Hence, the correct answer is PS I.

10. Choose the Correct Statements:
Statement I: PS II absorbs light at 700 nm.
Statement II: PS I absorbs light at 680 nm.
1. Both are true
2. Both are false
3. Statement I true, II false
4. Statement I false, II true
Explanation:
PS II absorbs light at 680 nm (P680), and PS I absorbs light at 700 nm (P700). Therefore, both statements are false. Correct answer: option 2.

Subtopic: Enzymes and C4 Photosynthesis

• RuBisCO: Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme involved in carbon fixation during photosynthesis.

• Photorespiration: A process in which RuBisCO oxygenates RuBP, leading to loss of fixed CO₂ in plants.

• C4 Plants: Plants that use the C4 pathway to efficiently fix CO₂ in mesophyll and bundle sheath cells.

• Enzyme: A protein that acts as a catalyst to accelerate biochemical reactions without being consumed.

• Carbon Fixation: The process of converting inorganic CO₂ into organic compounds during photosynthesis.

• Mesophyll Cells: Photosynthetic cells in leaves where CO₂ is initially fixed in C4 plants.

• Bundle Sheath Cells: Specialized cells surrounding leaf veins in C4 plants where Calvin cycle occurs.

• Calvin Cycle: The light-independent reactions of photosynthesis that convert CO₂ into glucose.

• Oxygenation: The reaction of RuBisCO with O₂ instead of CO₂, leading to photorespiration.

• Light Reaction: The initial stage of photosynthesis that converts light energy into chemical energy (ATP & NADPH).

• Carbon Dioxide (CO₂): A gas essential for photosynthesis, serving as the carbon source for carbohydrate formation.

Lead Question - 2023 (Manipur)

Given below are two statements :

Statement I: RuBisCO is the most abundant enzyme in the world.

Statement II: Photorespiration does not occur in C4 plants.

In the light of the above statements, choose the most appropriate answer from the options given below:

• 1. Statement I is correct but Statement II is incorrect

• 2. Statement I is incorrect but Statement II is correct

• 3. Both Statement I and Statement II are correct

• 4. Both Statement I and Statement II are incorrect

Explanation: RuBisCO is indeed the most abundant enzyme on Earth and catalyzes CO₂ fixation in the Calvin cycle. Photorespiration is largely minimized in C4 plants due to spatial separation of initial CO₂ fixation in mesophyll cells and the Calvin cycle in bundle sheath cells. Hence, both statements are correct. The correct answer is 3.

1. Which of the following is the primary CO₂-fixing enzyme in C3 plants?

• a) PEP carboxylase

• b) RuBisCO

• c) NADP reductase

• d) ATP synthase

Explanation: In C3 plants, RuBisCO catalyzes the fixation of CO₂ into 3-phosphoglycerate during the Calvin cycle. PEP carboxylase functions in C4 plants for initial CO₂ fixation. NADP reductase and ATP synthase are involved in light reactions, not carbon fixation. Correct answer: b.

2. Which cell type in C4 plants contains the Calvin cycle enzymes?

• a) Mesophyll cells

• b) Bundle sheath cells

• c) Guard cells

• d) Epidermal cells

Explanation: In C4 plants, the Calvin cycle occurs in bundle sheath cells, while initial CO₂ fixation occurs in mesophyll cells. Guard cells and epidermal cells are not involved in the Calvin cycle. This spatial separation reduces photorespiration. Correct answer: b.

3. PEP carboxylase in C4 plants functions primarily to:

• a) Fix oxygen

• b) Fix CO₂ into oxaloacetate

• c) Produce ATP

• d) Release CO₂

Explanation: PEP carboxylase catalyzes the fixation of CO₂ into oxaloacetate in mesophyll cells of C4 plants, which is then transported to bundle sheath cells for the Calvin cycle. It does not fix oxygen or produce ATP. Correct answer: b.

4. Which of the following increases in C4 plants compared to C3 plants?

• a) Photorespiration rate

• b) CO₂ concentration in bundle sheath cells

• c) Oxygenation of RuBP

• d) Water loss per CO₂ fixed

Explanation: C4 plants concentrate CO₂ in bundle sheath cells, which suppresses photorespiration and reduces oxygenation of RuBP. Water use efficiency is higher. Photorespiration is lower, not higher. Correct answer: b.

5. The first stable product of C3 photosynthesis is:

• a) 3-Phosphoglycerate

• b) Oxaloacetate

• c) Malate

• d) Glucose

Explanation: In C3 plants, CO₂ fixation by RuBisCO produces 3-phosphoglycerate (3-PGA) as the first stable product. Oxaloacetate and malate are products in C4 metabolism, while glucose is formed later in the Calvin cycle. Correct answer: a.

6. Which of the following reduces photorespiration?

• a) High O₂ concentration

• b) C4 pathway

• c) Low CO₂ concentration

• d) High temperature alone

Explanation: The C4 pathway spatially separates CO₂ fixation and the Calvin cycle, increasing CO₂ concentration near RuBisCO, thereby reducing photorespiration. High O₂, low CO₂, and high temperature alone increase photorespiration. Correct answer: b.

7. Assertion (A): C4 plants have Kranz anatomy.
Reason (R): Bundle sheath cells are surrounded by mesophyll cells in a wreath-like arrangement.

• a) Both A and R are true, and R is the correct explanation of A

• b) Both A and R are true, but R is not the correct explanation of A

• c) A is true, R is false

• d) A is false, R is true

Explanation: C4 plants exhibit Kranz anatomy, where bundle sheath cells are surrounded by mesophyll cells in a wreath-like pattern. This arrangement facilitates efficient CO₂ transfer to bundle sheath cells, reducing photorespiration. Both assertion and reason are true, and the reason correctly explains the assertion. Correct answer: a.

8. Match the following:

• Column I: 1. C3 plant 2. C4 plant 3. CAM plant

• Column II: a. Malate accumulation at night b. First stable product is 3-PGA c. CO₂ fixed as oxaloacetate in mesophyll

Choices:
a) 1-b, 2-c, 3-a
b) 1-c, 2-b, 3-a
c) 1-a, 2-b, 3-c
d) 1-b, 2-a, 3-c

Explanation: In C3 plants, the first stable product is 3-PGA. In C4 plants, CO₂ is initially fixed as oxaloacetate. CAM plants accumulate malate at night to fix CO₂ temporally. Matching yields: 1-b, 2-c, 3-a. Correct answer: a.

9. Fill in the blank: In C4 plants, CO₂ is first fixed by ________ in mesophyll cells.

• a) RuBisCO

• b) PEP carboxylase

• c) NADP reductase

• d) ATP synthase

Explanation: In C4 plants, CO₂ is initially fixed in mesophyll cells by PEP carboxylase to form oxaloacetate, which is later converted into malate or aspartate. This mechanism ensures high CO₂ concentration near RuBisCO in bundle sheath cells, reducing photorespiration. Correct answer: b.

10. Choose the correct statements:

Statement I: C4 plants are more efficient than C3 plants under high temperature and light.
Statement II: CAM plants open stomata at night to conserve water.

• a) Both Statement I and Statement II are correct

• b) Statement I is correct, Statement II is incorrect

• c) Statement I is incorrect, Statement II is correct

• d) Both Statement I and Statement II are incorrect

Explanation: C4 plants minimize photorespiration and are more efficient than C3 plants under high temperature and light. CAM plants open stomata at night to fix CO₂, conserving water in arid conditions. Both statements are correct. Correct answer: a.

Topic: Plant Pigments; Subtopic: Types and Functions of Pigments

Keyword Definitions:
• Chlorophyll a: Primary photosynthetic pigment, absorbs blue-violet and red light, reflects blue-green color.
• Chlorophyll b: Accessory pigment, absorbs light of wavelengths not absorbed by chlorophyll a, appears yellow-green.
• Xanthophyll: Yellow pigments in plants, a type of carotenoid, protects against photooxidative damage.
• Carotenoids: Orange to yellow pigments, include carotenes and xanthophylls, assist in light capture and photoprotection.
• Photosynthesis: Process of converting light energy to chemical energy in plants.
• Accessory pigments: Pigments that assist chlorophyll in capturing light energy.
• Blue-green color: Typical of chlorophyll a due to its absorption spectrum.
• Yellow-green color: Characteristic of chlorophyll b reflecting specific light wavelengths.

Lead Question - 2023 (Manipur)
Match List-I with List-II
List-I List-II
(A) Chlorophyll a (I) Yellow to yellow orange
(B) Chlorophyll b (II) Yellow green
(C) Xanthophyll (III) Blue green
(D) Carotenoids (IV) Yellow
Choose the correct answer from the options given below:
Options: (A) (B) (C) (D)
1. III II IV I
2. III I IV II
3. II III I IV
4. IV III II I
Answer & Explanation: Option 1. Chlorophyll a appears blue-green (III), chlorophyll b is yellow-green (II), xanthophyll is yellow (IV), and carotenoids appear yellow to yellow-orange (I). These pigments absorb specific wavelengths to drive photosynthesis and protect chlorophyll from photooxidation. Understanding pigment colors and functions is essential for studying light absorption, energy transfer, and plant physiology. Chlorophylls are primary pigments, while xanthophylls and carotenes are accessory pigments assisting in photoprotection. Knowledge of pigment types aids in botanical identification, research in plant biochemistry, and practical applications like optimizing crop growth under various light conditions.

1. Single Correct Answer MCQ
Which pigment primarily absorbs light for photosynthesis?
Options:
A. Xanthophyll
B. Carotenoids
C. Chlorophyll a
D. Anthocyanins
Answer & Explanation: Option C. Chlorophyll a is the main photosynthetic pigment that absorbs light energy, mainly blue-violet and red wavelengths, driving the light reactions. Accessory pigments like chlorophyll b and carotenoids extend light absorption range. Understanding chlorophyll a is critical in plant physiology, photosynthesis studies, and agricultural applications. Its presence and efficiency determine the rate of energy capture, production of ATP and NADPH, and overall plant productivity. Knowledge of primary and accessory pigments helps explain plant coloration, energy transfer, and adaptation to different light environments.

2. Single Correct Answer MCQ
Xanthophyll pigments primarily appear:
Options:
A. Blue-green
B. Yellow
C. Red
D. Purple
Answer & Explanation: Option B. Xanthophylls are yellow pigments belonging to carotenoids. They protect chlorophyll from photooxidation and assist in light absorption. Their yellow coloration is visible in leaves and other plant parts. Xanthophylls play a role in non-photochemical quenching, dissipating excess light energy safely. Knowledge of xanthophylls is important for understanding plant photoprotection, seasonal leaf color changes, and adaptation to high-light environments. These pigments help maintain photosynthetic efficiency, prevent oxidative damage, and ensure plant survival under varying light intensities.

3. Single Correct Answer MCQ
Carotenoids include:
Options:
A. Chlorophyll a
B. Xanthophylls and carotenes
C. Chlorophyll b
D. Anthocyanins
Answer & Explanation: Option B. Carotenoids comprise xanthophylls and carotenes, appearing yellow, orange, or red. They assist chlorophyll in light absorption, protect from photodamage, and contribute to leaf and fruit coloration. Recognizing carotenoids helps in plant physiology, understanding light harvesting, and photoprotection mechanisms. Carotenoids’ structural properties allow energy transfer to chlorophyll a and protection against reactive oxygen species. Studying these pigments aids in understanding photosynthesis efficiency, seasonal leaf color changes, and breeding crops with optimized pigment composition for improved photosynthetic performance and stress tolerance.

4. Single Correct Answer MCQ
Which pigment reflects yellow-green light?
Options:
A. Chlorophyll a
B. Chlorophyll b
C. Carotenoids
D. Anthocyanins
Answer & Explanation: Option B. Chlorophyll b reflects yellow-green light, complementing chlorophyll a by absorbing light wavelengths not captured by it. It broadens the spectrum of absorbed light, increasing photosynthetic efficiency. Chlorophyll b acts as an accessory pigment, transferring energy to chlorophyll a. Understanding chlorophyll b is important in studying photosynthetic adaptation, leaf coloration, and plant growth under different light conditions. Its absorption characteristics help optimize energy capture, ensure effective photochemistry, and influence seasonal leaf color variations.

5. Single Correct Answer MCQ
Chlorophyll a appears in which color?
Options:
A. Yellow
B. Yellow-green
C. Blue-green
D. Red
Answer & Explanation: Option C. Chlorophyll a reflects blue-green color due to its absorption spectrum. It is the primary pigment driving photosynthesis by converting light energy into chemical energy. Blue-green coloration distinguishes chlorophyll a from chlorophyll b and accessory pigments. Understanding its color and absorption is essential for studying light harvesting, energy transfer, and plant physiology. Chlorophyll a concentration affects photosynthetic rate, biomass production, and crop productivity. This knowledge is critical in plant science, agriculture, and understanding adaptations to diverse light environments.

6. Single Correct Answer MCQ
Which pigment helps in photoprotection?
Options:
A. Chlorophyll a
B. Chlorophyll b
C. Carotenoids
D. None
Answer & Explanation: Option C. Carotenoids, including xanthophylls, protect chlorophyll from photooxidative damage by dissipating excess light energy safely. They absorb blue and green light, stabilize the photosynthetic apparatus, and prevent reactive oxygen species formation. Photoprotection ensures photosynthetic efficiency and plant survival under high-light stress. Recognizing carotenoids’ role is crucial for studying plant physiology, breeding stress-tolerant crops, and understanding adaptations in different light conditions. They complement chlorophylls in energy capture while safeguarding the photosynthetic machinery, highlighting the functional diversity of plant pigments.

7. Assertion-Reason MCQ
Assertion (A): Chlorophyll b acts as an accessory pigment.
Reason (R): Chlorophyll b absorbs light wavelengths not absorbed by chlorophyll a.
Options:
A. Both A and R are true, R is the correct explanation of A
B. Both A and R are true, R is not the correct explanation of A
C. A is true, R is false
D. A is false, R is true
Answer & Explanation: Option A. Chlorophyll b functions as an accessory pigment, capturing light wavelengths that chlorophyll a cannot, transferring this energy efficiently to chlorophyll a. This extends the range of absorbed light, enhancing photosynthetic efficiency. Understanding accessory pigments like chlorophyll b helps in studying light capture, energy transfer, and adaptation to low-light environments. Knowledge of pigment interactions is important for plant physiology, photosynthesis optimization, and crop productivity enhancement. Accessory pigments also play a role in seasonal leaf coloration and stress response mechanisms in plants.

8. Matching Type MCQ
Match pigments with their reflected colors:
List-I List-II
(A) Chlorophyll a (I) Yellow
(B) Chlorophyll b (II) Yellow-green
(C) Xanthophyll (III) Blue-green
(D) Carotenoids (IV) Yellow to yellow-orange
Options:
1. A-III, B-II, C-I, D-IV
2. A-II, B-III, C-IV, D-I
3. A-IV, B-I, C-II, D-III
4. A-I, B-IV, C-III, D-II
Answer & Explanation: Option 1. Chlorophyll a reflects blue-green (III), chlorophyll b yellow-green (II), xanthophyll yellow (I), and carotenoids yellow to yellow-orange (IV). Matching pigments to their colors is fundamental in plant physiology and photosynthesis studies. It helps in identifying pigments, understanding light absorption, energy transfer, and photoprotection mechanisms. Knowledge of pigment colors assists in studying seasonal leaf color changes, plant adaptations to light environments, and optimizing crop growth. Pigment identification is also essential in botany, ecology, and agricultural research.

9. Fill in the Blanks / Completion MCQ
The pigment responsible for yellow to yellow-orange coloration is _______.
Options:
A. Chlorophyll a
B. Chlorophyll b
C. Carotenoids
D. Anthocyanins
Answer & Explanation: Option C. Carotenoids, including carotenes and xanthophylls, provide yellow to yellow-orange coloration. They assist in light harvesting, energy transfer, and photoprotection. Recognizing carotenoids is important in plant physiology, photosynthesis research, and understanding plant adaptations. They complement chlorophylls by capturing additional light wavelengths and protecting photosynthetic machinery. Carotenoids’ coloration also contributes to seasonal leaf color changes, flower and fruit pigmentation, and ecological interactions such as attracting pollinators. Knowledge of pigment functions supports botany, horticulture, and crop improvement studies.

10. Choose the Correct Statements MCQ
Statement I: Chlorophyll a reflects blue-green color.
Statement II: Xanthophylls are yellow pigments that protect chlorophyll from photooxidation.
Options:
A. Both I and II are correct
B. Only I is correct
C. Only II is correct
D. Both I and II are incorrect
Answer & Explanation: Option A. Chlorophyll a reflects blue-green and drives photosynthesis, while xanthophylls are yellow pigments providing photoprotection. Both play crucial roles in light absorption, energy transfer, and protection against oxidative stress. Understanding pigment properties aids in plant physiology, ecology, and crop optimization. Their interplay ensures efficient photosynthesis, adaptation to light conditions, and survival under stress. Recognizing these pigment functions is fundamental for studying plant biochemistry, ecological interactions, and agricultural productivity, highlighting the importance of primary and accessory pigments in photosynthetic organisms.

Topic: Photosynthesis; Subtopic: Chemiosmosis and ATP Synthesis

Keyword Definitions:

• Chemiosmosis: Movement of protons across a membrane down their electrochemical gradient to generate ATP.

• Proton pump: Membrane protein complex that actively transports protons to create a proton gradient.

• ATP synthase: Enzyme complex that synthesizes ATP using the energy from proton flow.

• Proton gradient: Difference in proton concentration across a membrane, driving ATP formation.

• Electron transport chain: Series of protein complexes transferring electrons and pumping protons to create a gradient.

• Thylakoid membrane: Membrane system in chloroplast where chemiosmosis occurs during photosynthesis.

• Light reactions: Phase of photosynthesis producing ATP and NADPH using light energy.

• NADP+ Electron carrier reduced to NADPH during light reactions.

• Photophosphorylation: Process of ATP synthesis linked with light-driven electron transport.

• Electrochemical potential: Energy stored in proton gradient used by ATP synthase.

• Membrane: Biological barrier where chemiosmosis occurs, maintaining proton gradient.

Lead Question - 2023:

Which of the following combination is required for chemiosmosis?
(1) Proton pump, electron gradient, ATP synthase
(2) Proton pump, electron gradient, NADP synthase
(3) Membrane, proton pump, proton gradient, ATP synthase
(4) Membrane, proton pump, proton gradient, NADP synthase

Answer & Explanation: (3) Membrane, proton pump, proton gradient, ATP synthase. Chemiosmosis involves the movement of protons across a membrane (thylakoid) through ATP synthase. Proton pumps create a proton gradient via electron transport, and ATP synthase utilizes this gradient to synthesize ATP. NADP synthase is not involved. This process links light-driven electron transport to ATP formation. The membrane maintains the gradient, enabling energy conversion. Photophosphorylation occurs in chloroplasts during light reactions. Proper function of chemiosmosis requires all four components working together to generate ATP efficiently.

1. Which component directly synthesizes ATP in chemiosmosis?
(1) Proton pump
(2) ATP synthase
(3) Electron transport chain
(4) NADP reductase
Explanation: ATP synthase catalyzes the formation of ATP using the proton gradient generated by proton pumps. Correct answer is (2).

2. Proton gradient in chloroplasts is generated by:
(1) ATP synthase
(2) Electron transport chain and proton pump
(3) NADP+ reduction
(4) Calvin cycle
Explanation: Electron transport chain transfers electrons, while proton pumps move protons into the thylakoid lumen, establishing a proton gradient. Correct answer is (2).

3. Chemiosmosis occurs across which membrane?
(1) Plasma membrane
(2) Thylakoid membrane
(3) Mitochondrial matrix
(4) Outer chloroplast membrane
Explanation: In chloroplasts, chemiosmosis occurs across the thylakoid membrane where proton gradients drive ATP synthesis. Correct answer is (2).

4. Light-driven ATP synthesis is called:
(1) Substrate-level phosphorylation
(2) Oxidative phosphorylation
(3) Photophosphorylation
(4) Glycolysis
Explanation: ATP formation using light energy and proton gradients in chloroplasts is photophosphorylation. Correct answer is (3).

5. Which molecule is reduced in light reactions alongside chemiosmosis?
(1) NADP+
(2) ATP
(3) ADP
(4) CO2
Explanation: NADP+ accepts electrons and is reduced to NADPH during light reactions, working alongside ATP formation via chemiosmosis. Correct answer is (1).

6. The energy driving proton movement comes from:
(1) ATP hydrolysis
(2) Electron transport
(3) Calvin cycle
(4) Carbon fixation
Explanation: Electron transport through photosystems releases energy that drives proton pumping, creating a gradient for ATP synthesis. Correct answer is (2).

Assertion-Reason Type Question
7. Assertion (A): Chemiosmosis requires a membrane-bound proton gradient.
Reason (R): Proton movement through ATP synthase generates ATP from ADP and Pi.
(1) Both A and R true, R explains A
(2) Both A and R true, R does not explain A
(3) A true, R false
(4) A false, R true
Explanation: The proton gradient across the thylakoid membrane is essential. Protons flow through ATP synthase to produce ATP. Both A and R are correct, and R explains A. Correct answer is (1).

Matching Type Question
8. Match component with its function:
A. Proton pump – i. Synthesizes ATP
B. ATP synthase – ii. Creates proton gradient
C. Electron transport – iii. Transfers electrons
D. Proton gradient – iv. Drives ATP formation
(1) A-ii, B-i, C-iii, D-iv
(2) A-iii, B-ii, C-i, D-iv
(3) A-i, B-iv, C-ii, D-iii
(4) A-iv, B-iii, C-ii, D-i
Explanation: Proton pump creates gradient (A-ii), ATP synthase makes ATP (B-i), electron transport moves electrons (C-iii), gradient drives ATP formation (D-iv). Correct answer is (1).

Fill in the Blanks Question
9. The enzyme that uses the proton gradient to produce ATP is _______.
(1) NADP reductase
(2) ATP synthase
(3) Rubisco
(4) Phosphofructokinase
Explanation: ATP synthase catalyzes the phosphorylation of ADP using energy from proton flow. Correct answer is (2).

Choose the Correct Statements Question
10. Statement I: Chemiosmosis requires a membrane and a proton gradient.
Statement II: NADP+ acts as the direct proton acceptor in chemiosmosis.
(1) Both I and II correct
(2) Only I correct
(3) Only II correct
(4) Neither I nor II correct
Explanation: Membrane and proton gradient are essential for chemiosmosis (I correct). NADP+ accepts electrons, not protons, so II is incorrect. Correct answer is (2).

Chapter: Photosynthesis; Topic: Light Reactions; Subtopic: Photosystem II

Keyword Definitions:

• Photosystem II (PS II): A protein-pigment complex in the thylakoid membrane that absorbs light and initiates electron transport.

• Reaction Centre: The core of a photosystem containing chlorophyll molecules where primary photochemistry occurs.

• Absorption Maxima: Wavelength at which a pigment absorbs light most efficiently.

• Chlorophyll a: Primary pigment in photosystems responsible for light absorption.

• Thylakoid Membrane: Membrane system within chloroplasts where light reactions occur.

• Electron Transport Chain: Series of protein complexes transferring electrons to produce ATP and NADPH.

• Photolysis: Splitting of water molecules by light energy to release oxygen.

• ATP Synthesis: Production of ATP by chemiosmosis using a proton gradient in chloroplasts.

• NADPH Formation: Reduction of NADP⁺ to NADPH during light reactions.

• Photosystem I (PS I): Another photosystem with a reaction centre absorbing at a different wavelength (700 nm).

• Light Reactions: Stage of photosynthesis capturing light energy to form ATP and NADPH.

Lead Question - 2023:

The reaction centre in PS II has an absorption maxima at:
(1) 660 nm
(2) 780 nm
(3) 680 nm
(4) 700 nm

Answer & Explanation: (3) 680 nm. Photosystem II reaction centre, also called P680, has its absorption peak at 680 nm in the red region of the light spectrum. It plays a key role in initiating electron transport by exciting electrons using absorbed light energy. This energy drives photolysis of water and oxygen evolution, and contributes to the formation of ATP and NADPH. Correct identification of P680 is essential to understand energy capture in photosynthesis. Other options correspond to chlorophyll peaks in different contexts, such as P700 for PS I or accessory pigments. P680 is specific to PS II.

1. Primary pigment in PS II is:
(1) Chlorophyll a
(2) Chlorophyll b
(3) Carotenoids
(4) Xanthophylls
Explanation: Chlorophyll a is the main pigment in PS II, absorbing light primarily at 680 nm and initiating photochemical reactions. Correct answer is (1).

2. Oxygen is released during PS II due to:
(1) NADPH formation
(2) ATP synthesis
(3) Photolysis of water
(4) Electron transport in PS I
Explanation: PS II splits water molecules via photolysis to release oxygen, electrons, and protons. Correct answer is (3).

3. P680 refers to:
(1) Wavelength of PS I reaction centre
(2) Wavelength of PS II reaction centre
(3) Peak of chlorophyll b
(4) Carotenoid absorption peak
Explanation: P680 denotes PS II reaction centre chlorophyll a with absorption maxima at 680 nm. Correct answer is (2).

4. Location of PS II:
(1) Stroma
(2) Thylakoid membrane
(3) Cytoplasm
(4) Inner mitochondrial membrane
Explanation: PS II is embedded in the thylakoid membrane, facilitating light capture and electron transport. Correct answer is (2).

5. Electron acceptor in PS II is:
(1) NADP⁺
(2) Plastoquinone
(3) Oxygen
(4) Cytochrome b6f
Explanation: Plastoquinone receives electrons from excited P680 in PS II, transferring them along the electron transport chain. Correct answer is (2).

6. Accessory pigments in PS II include:
(1) Carotenoids and chlorophyll b
(2) NADP⁺ and FAD
(3) ATP and ADP
(4) P700 only
Explanation: Carotenoids and chlorophyll b complement P680 by absorbing additional wavelengths and transferring energy. Correct answer is (1).

Assertion-Reason Type Question
7. Assertion (A): PS II initiates photolysis of water.
Reason (R): P680 absorbs light at 680 nm and excites electrons.
(1) Both A and R are true and R explains A
(2) Both A and R are true but R does not explain A
(3) A is true, R is false
(4) A is false, R is true
Explanation: PS II uses energy absorbed by P680 at 680 nm to excite electrons, which triggers water splitting. Both statements are correct, and R explains A. Correct answer is (1).

Matching Type Question
8. Match Photosystem with reaction centre:
A. PS II – (i) P700
B. PS I – (ii) P680
(1) A-(ii), B-(i)
(2) A-(i), B-(ii)
(3) Both A and B-(i)
(4) Both A and B-(ii)
Explanation: PS II has P680, and PS I has P700 as reaction centres. Correct answer is (1).

Fill in the Blanks Question
9. The reaction centre of PS II is called _______ because it absorbs light maximally at 680 nm.
(1) P700
(2) P680
(3) Chlorophyll b
(4) Carotenoid
Explanation: PS II reaction centre chlorophyll a is called P680 for its absorption maxima at 680 nm. Correct answer is (2).

Choose the Correct Statements Question
10. Statement I: P680 absorbs light in the red region.
Statement II: PS II generates ATP and oxygen.
(1) Both statements are true
(2) Statement I true, Statement II false
(3) Statement I false, Statement II true
(4) Both statements are false
Explanation: P680 absorbs red light at 680 nm, and PS II initiates photolysis of water and electron transport leading to ATP production. Both statements are correct. Correct answer is (1).

Chapter: Photosynthesis; Topic: Light Reactions; Subtopic: Role of Micronutrients

Keyword Definitions:

• Photosynthesis: Process by which green plants convert light energy into chemical energy, producing glucose and oxygen.

• Light Reactions: Phase of photosynthesis occurring in thylakoid membranes where light energy splits water and generates ATP & NADPH.

• Water Splitting: Photolysis of water in photosystem II, producing electrons, protons, and oxygen.

• Micronutrient: Essential elements required in small amounts for enzymatic functions and metabolic processes in plants.

• Magnesium: Central atom in chlorophyll molecule, essential for light absorption.

• Copper: Trace element required in electron transport components.

• Manganese: Micronutrient involved in water-splitting in photosystem II.

• Molybdenum: Required for nitrate reduction in plants.

• Thylakoid membrane: Membrane within chloroplasts where light-dependent reactions occur.

• ATP: Adenosine triphosphate, energy currency of cells.

• NADPH: Reduced nicotinamide adenine dinucleotide phosphate, electron carrier in photosynthesis.

Lead Question - 2023:

Which micronutrient is required for splitting of water molecule during photosynthesis?
(1) Magnesium
(2) Copper
(3) Manganese
(4) Molybdenum

Answer & Explanation: (3) Manganese. Manganese is a crucial component of the oxygen-evolving complex (OEC) in photosystem II. It catalyzes the splitting of water molecules into electrons, protons, and molecular oxygen during the light-dependent reactions. Magnesium, although central in chlorophyll, does not participate directly in water-splitting. Copper functions in plastocyanin and electron transport, while molybdenum is important for nitrate reduction. Without manganese, the photolysis of water cannot occur efficiently, leading to failure in electron supply for photosynthesis. This highlights its indispensable role in energy capture and oxygen evolution in plants.

1. Which micronutrient forms the central atom of chlorophyll?
(1) Magnesium
(2) Manganese
(3) Copper
(4) Iron
Explanation: Magnesium forms the central atom of the chlorophyll molecule and is essential for light absorption during photosynthesis. It does not split water; that role belongs to manganese. Correct answer is (1).

2. Copper in photosynthesis is required for:
(1) Water splitting
(2) Plastocyanin electron transport
(3) NADPH formation
(4) Oxygen evolution
Explanation: Copper is a component of plastocyanin, a protein in the electron transport chain, transferring electrons from photosystem II to photosystem I. It does not participate in water splitting. Correct answer is (2).

3. Molybdenum is essential for plants mainly in:
(1) Water splitting
(2) Nitrate reduction
(3) ATP synthesis
(4) Electron transport
Explanation: Molybdenum acts as a cofactor for nitrate reductase enzyme, facilitating nitrate reduction into ammonium. It does not participate in splitting water or light reactions. Correct answer is (2).

4. The oxygen-evolving complex in photosystem II contains:
(1) Magnesium
(2) Manganese
(3) Copper
(4) Zinc
Explanation: The oxygen-evolving complex (OEC) in photosystem II contains manganese ions that catalyze water photolysis into electrons, protons, and oxygen. Magnesium is part of chlorophyll but not OEC. Correct answer is (2).

5. Light-dependent reactions occur in:
(1) Cytoplasm
(2) Thylakoid membrane
(3) Mitochondria
(4) Nucleus
Explanation: Light-dependent reactions of photosynthesis occur in the thylakoid membrane of chloroplasts where water is split, ATP is generated, and NADPH is produced. Correct answer is (2).

6. Electrons for photosystem II are obtained from:
(1) NADPH
(2) Water molecules
(3) Carbon dioxide
(4) Oxygen
Explanation: Electrons for photosystem II are obtained from water molecules, which are split by the oxygen-evolving complex containing manganese. This provides electrons for the electron transport chain. Correct answer is (2).

Assertion-Reason Type Question
7. Assertion (A): Manganese is essential for photolysis of water.
Reason (R): Manganese acts as a cofactor in the oxygen-evolving complex of photosystem II.
(1) Both A and R are true, and R is correct explanation of A
(2) Both A and R are true, but R is not correct explanation of A
(3) A is true but R is false
(4) A is false but R is true
Explanation: Manganese is a key component of the oxygen-evolving complex in photosystem II, directly catalyzing water splitting. Both the assertion and reason are true, and R correctly explains A. Correct answer is (1).

Matching Type Question
8. Match the micronutrient with its primary function:
A. Magnesium – (i) Water splitting
B. Manganese – (ii) Chlorophyll center
C. Copper – (iii) Electron transport
D. Molybdenum – (iv) Nitrate reduction
(1) A-(ii), B-(i), C-(iii), D-(iv)
(2) A-(i), B-(ii), C-(iv), D-(iii)
(3) A-(iii), B-(iv), C-(ii), D-(i)
(4) A-(iv), B-(iii), C-(i), D-(ii)
Explanation: Magnesium is central in chlorophyll, manganese catalyzes water splitting, copper participates in electron transport via plastocyanin, and molybdenum is required for nitrate reduction. Correct answer is (1).

Fill in the Blanks Question
9. The micronutrient essential for splitting water in photosystem II is ______.
(1) Magnesium
(2) Copper
(3) Manganese
(4) Iron
Explanation: Manganese is essential in the oxygen-evolving complex to catalyze water photolysis in photosystem II. Correct answer is (3).

Choose the Correct Statements Question
10. Statement I: Manganese is required for splitting water in light reactions.
Statement II: Magnesium is part of chlorophyll but not directly involved in water splitting.
(1) Both statements are true
(2) Statement I is true, Statement II is false
(3) Statement I is false, Statement II is true
(4) Both statements are false
Explanation: Manganese catalyzes water photolysis in photosystem II, while magnesium forms the central atom of chlorophyll, aiding light absorption but not water splitting. Both statements are true. Correct answer is (1).

Chapter: Photosynthesis in Higher Plants; Topic: Calvin Cycle; Subtopic: Energy Requirement for Glucose Synthesis

Keyword Definitions:

• Calvin Cycle: The dark reaction of photosynthesis that occurs in the stroma of chloroplasts to form glucose.

• ATP (Adenosine Triphosphate): The main energy currency of cells used to drive biosynthetic reactions.

• NADPH2: The reduced form of NADP+ that provides hydrogen and electrons during carbon fixation.

• Glucose Synthesis: The final product of photosynthesis formed through multiple enzymatic reactions involving CO2 fixation.

Lead Question - 2023:

How many ATP and NADPH2 are required for the synthesis of one molecule of glucose during the Calvin cycle?
(1) 12 ATP and 16 NADPH2
(2) 18 ATP and 16 NADPH2
(3) 12 ATP and 12 NADPH2
(4) 18 ATP and 12 NADPH2

Explanation: The Calvin cycle fixes six molecules of CO2 to form one glucose molecule. Each CO2 requires 3 ATP and 2 NADPH2. Thus, 6 CO2 require 18 ATP and 12 NADPH2. ATP provides energy for carbon fixation and sugar formation, while NADPH2 donates reducing power for biosynthesis. Hence, the correct answer is (4) 18 ATP and 12 NADPH2.

1. Which of the following is the site of the Calvin cycle?
(1) Thylakoid membrane
(2) Stroma of chloroplast
(3) Cytoplasm
(4) Mitochondria
Explanation: The Calvin cycle takes place in the stroma of the chloroplast, where enzymes like RuBisCO catalyze carbon fixation using ATP and NADPH from light reactions. The stroma provides necessary substrates and conditions for glucose synthesis. Hence, the correct answer is (2) Stroma of chloroplast.

2. Which enzyme catalyzes the first step of the Calvin cycle?
(1) PEP carboxylase
(2) RuBisCO
(3) ATP synthase
(4) Hexokinase
Explanation: RuBisCO (Ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyzes the first step of the Calvin cycle by combining CO2 with RuBP to form 3-phosphoglycerate. It is the most abundant enzyme on Earth and plays a key role in carbon fixation. Hence, the correct answer is (2) RuBisCO.

3. In the Calvin cycle, CO2 is fixed to form which compound initially?
(1) 3-Phosphoglycerate
(2) Glucose
(3) Fructose
(4) Ribulose bisphosphate
Explanation: The enzyme RuBisCO fixes CO2 to ribulose-1,5-bisphosphate (RuBP), forming an unstable six-carbon compound that immediately splits into two molecules of 3-phosphoglycerate (3-PGA). Thus, the first stable compound formed is 3-phosphoglycerate. Hence, the correct answer is (1) 3-Phosphoglycerate.

4. How many turns of the Calvin cycle are required to produce one glucose molecule?
(1) 3 turns
(2) 6 turns
(3) 9 turns
(4) 12 turns
Explanation: Each turn of the Calvin cycle fixes one molecule of CO2. Since one glucose molecule contains six carbon atoms, six CO2 molecules must be fixed, requiring six complete turns of the cycle. Hence, the correct answer is (2) 6 turns.

5. Which phase of the Calvin cycle involves the regeneration of RuBP?
(1) Carboxylation
(2) Reduction
(3) Regeneration
(4) Oxidation
Explanation: The regeneration phase of the Calvin cycle restores RuBP, the acceptor molecule of CO2, enabling continuous carbon fixation. ATP is used to rearrange carbon skeletons to form RuBP from G3P. Hence, the correct answer is (3) Regeneration.

6. Which compound is directly used to synthesize glucose in the Calvin cycle?
(1) 3-PGA
(2) G3P (Glyceraldehyde-3-phosphate)
(3) RuBP
(4) Pyruvate
Explanation: G3P (Glyceraldehyde-3-phosphate) is the direct product of the Calvin cycle. Two molecules of G3P combine to form one glucose molecule. It serves as a precursor for several carbohydrates and biomolecules. Hence, the correct answer is (2) G3P.

Assertion-Reason Type Question
7. Assertion (A): ATP and NADPH are produced in the light reaction.
Reason (R): Both ATP and NADPH are used in dark reactions for carbon fixation.
(1) Both A and R are true, and R is the correct explanation of A.
(2) Both A and R are true, but R is not the correct explanation of A.
(3) A is true but R is false.
(4) A is false but R is true.
Explanation: ATP and NADPH are generated during the light-dependent reactions of photosynthesis and utilized in the Calvin cycle to convert CO2 into glucose. Thus, both statements are true, and the reason correctly explains the assertion. Hence, the correct answer is (1).

Matching Type Question
8. Match the following:
A. Carboxylation – (i) Formation of RuBP
B. Reduction – (ii) Formation of G3P
C. Regeneration – (iii) CO2 fixation
(1) A-(iii), B-(ii), C-(i)
(2) A-(ii), B-(i), C-(iii)
(3) A-(i), B-(iii), C-(ii)
(4) A-(iii), B-(i), C-(ii)
Explanation: Carboxylation involves CO2 fixation forming 3-PGA, reduction forms G3P using ATP and NADPH, and regeneration reforms RuBP for continuity. Hence, A-(iii), B-(ii), C-(i) is correct. Thus, the correct answer is (1).

Fill in the Blanks Question
9. In the Calvin cycle, the enzyme ______ catalyzes the fixation of CO2.
(1) Hexokinase
(2) RuBisCO
(3) PEP carboxylase
(4) ATPase
Explanation: The enzyme RuBisCO catalyzes the fixation of CO2 with RuBP to form 3-PGA, the first stable product in the Calvin cycle. It is crucial for photosynthetic carbon assimilation. Hence, the correct answer is (2) RuBisCO.

Choose the Correct Statements Question
10. Statement I: The Calvin cycle occurs in the chloroplast stroma.
Statement II: ATP and NADPH are used in the regeneration of RuBP.
(1) Both statements are true.
(2) Statement I is true, Statement II is false.
(3) Statement I is false, Statement II is true.
(4) Both statements are false.
Explanation: The Calvin cycle occurs in the chloroplast stroma where ATP and NADPH are consumed in reduction and regeneration steps. Both statements correctly describe the process. Hence, the correct answer is (1) Both statements are true.

Chapter: Photosynthesis – Light Reactions; Topic: Chemiosmotic Hypothesis and Photophosphorylation; Subtopic: Proton Gradient and ATP Synthesis

Keyword Definitions:

• Chemiosmotic hypothesis: Theory explaining ATP synthesis using proton gradient across membranes.

• Thylakoid membrane: Membrane inside chloroplast where light reactions occur.

• Lumen: Interior space of thylakoids where protons accumulate.

• Stroma: Fluid-filled region of chloroplast outside thylakoids.

• Photophosphorylation: ATP production using light energy.

• Primary electron acceptor: Molecule in photosystem that receives electrons from excited chlorophyll.

• NADP reductase: Enzyme reducing NADP⁺ to NADPH.

• Proton gradient: Difference in proton concentration across membrane creating potential energy.

• ATP synthase: Enzyme that synthesizes ATP using proton motive force.

• Water splitting: Photolysis generating electrons, protons, and O₂.

• Electron transport chain: Series of molecules transferring electrons, pumping protons.

Lead Question - 2022 (Ganganagar)

Identify the correct statements regarding chemiosmotic hypothesis:

(a) Splitting of the water molecule takes place on the inner side of the membrane.

(b) Protons accumulate within the lumen of the thylakoids.

(c) Primary acceptor of electron transfers the electrons to an electron carrier.

(d) NADP reductase enzyme is located on the stroma side of the membrane.

(e) Protons increase in number in stroma.

1. (a), (b) and (e)

2. (a), (b) and (d)

3. (b), (c) and (d)

4. (b), (c) and (e)

Explanation: During light reactions, water is split by photolysis on the lumen side of thylakoids, releasing protons into the lumen, electrons to photosystem II, and oxygen. The primary electron acceptor passes electrons through the transport chain. NADP reductase on the stroma side reduces NADP⁺ to NADPH. Proton accumulation occurs in the lumen, not stroma, creating a gradient used by ATP synthase. Thus, correct statements are (b), (c), and (d), forming the basis of the chemiosmotic hypothesis explaining how light energy drives ATP synthesis via proton motive force. Correct answer is 3.

1. Single Correct Answer MCQ:

Where do protons accumulate during light reactions?

a) Stroma

b) Lumen of thylakoids

c) Cytoplasm

d) Outer chloroplast membrane

Explanation: Protons accumulate inside thylakoid lumen creating a gradient for ATP synthesis. Correct answer is b) Lumen of thylakoids.

2. Single Correct Answer MCQ:

The enzyme NADP reductase is located:

a) On lumen side

b) On stroma side

c) Embedded within thylakoid membrane

d) In cytoplasm

Explanation: NADP reductase reduces NADP⁺ to NADPH on the stroma side of the membrane. Correct answer is b) On stroma side.

3. Single Correct Answer MCQ:

The primary electron acceptor transfers electrons to:

a) NADP⁺

b) Electron transport chain

c) Water

d) Oxygen

Explanation: The primary acceptor transfers electrons to the electron transport chain, initiating the photophosphorylation process. Correct answer is b) Electron transport chain.

4. Single Correct Answer MCQ:

Which process generates the proton gradient in thylakoids?

a) Calvin cycle

b) Photolysis of water

c) CO₂ fixation

d) Photorespiration

Explanation: Photolysis of water releases protons into the lumen, creating the gradient used for ATP synthesis. Correct answer is b) Photolysis of water.

5. Single Correct Answer MCQ:

Which statement is false regarding chemiosmosis?

a) Protons move from lumen to stroma through ATP synthase

b) Proton gradient drives ATP synthesis

c) Protons accumulate in stroma

d) Light energy drives electron transport

Explanation: Protons accumulate in the lumen, not stroma. The gradient drives ATP synthase activity. Correct answer is c) Protons accumulate in stroma.

6. Single Correct Answer MCQ:

ATP synthase uses proton gradient to:

a) Reduce NADP⁺

b) Synthesize ATP

c) Split water

d) Excite chlorophyll

Explanation: ATP synthase harnesses proton motive force to generate ATP. Correct answer is b) Synthesize ATP.

7. Assertion-Reason MCQ:

Assertion (A): Protons accumulate in thylakoid lumen during light reactions.

Reason (R): Water photolysis releases protons into the lumen.

a) Both A and R true, R explains A

b) Both A and R true, R does not explain A

c) A true, R false

d) A false, R true

Explanation: Protons are released from water photolysis into lumen, creating the gradient for ATP synthesis. Correct answer is a) Both A and R true, R explains A.

8. Matching Type MCQ:

Match the molecule with its location:

Column I | Column II

A) NADP reductase | 1) Lumen side

B) ATP synthase | 2) Spanning membrane

C) Protons (H⁺) | 3) Lumen

Choices: A-__ B-__ C-__

Explanation: NADP reductase is on stroma side, ATP synthase spans membrane, protons accumulate in lumen. Correct matching: A-None of given (stroma side), B-2, C-3.

9. Fill in the Blanks / Completion MCQ:

ATP is synthesized as protons move from ______ to ______ through ATP synthase.

a) Stroma → lumen

b) Lumen → stroma

c) Cytoplasm → lumen

d) Lumen → cytoplasm

Explanation: Protons flow from lumen to stroma via ATP synthase, driving ATP production. Correct answer is b) Lumen → stroma.

10. Choose the correct statements MCQ (Statement I & II):

Statement I: Photolysis of water occurs on lumen side.

Statement II: Protons accumulate in stroma during chemiosmosis.

a) Both correct

b) Only I correct

c) Only II correct

d) Both incorrect

Explanation: Photolysis releases protons into lumen, not stroma. Only Statement I is correct. Correct answer is b) Only I correct. 

Topic: Photosynthesis; Subtopic: Calvin Cycle – Reduction Phase

Keyword Definitions:

• CO₂ fixation: Incorporation of carbon dioxide into organic molecules during photosynthesis.

• Triose phosphate: A three-carbon sugar (glyceraldehyde-3-phosphate, G3P) produced in the Calvin cycle.

• Reduction phase: Phase in the Calvin cycle where 3-phosphoglycerate is reduced to glyceraldehyde-3-phosphate using ATP and NADPH.

• ATP: Adenosine triphosphate, a high-energy molecule providing energy for biochemical reactions.

• NADPH: Nicotinamide adenine dinucleotide phosphate, an electron donor providing reducing power for biosynthetic reactions.

• Photochemically made intermediates: Molecules produced in light reactions of photosynthesis that supply energy and electrons for carbon fixation.

• Calvin cycle: Light-independent reactions of photosynthesis in chloroplast stroma that convert CO₂ into sugars.

Lead Question – 2022 (Ganganagar)
When one CO₂ molecule is fixed as one molecule of triose phosphate, which of the following photochemically made, high energy chemical intermediates are used in the reduction phase?
1. 1 ATP + 1 NADPH
2. 1 ATP + 2 NADPH
3. 2 ATP + 1 NADPH
4. 2 ATP + 2 NADPH

Explanation:
Correct answer is option 4. In the Calvin cycle, fixation of one CO₂ molecule requires conversion of 3-phosphoglycerate (3-PGA) to glyceraldehyde-3-phosphate (G3P) during the reduction phase. This process consumes 2 molecules of ATP to phosphorylate 3-PGA and 2 molecules of NADPH to reduce 1,3-bisphosphoglycerate into G3P. ATP provides the energy, while NADPH donates high-energy electrons. These photochemically produced intermediates are essential for the light-independent reactions, linking the energy captured during photosynthesis to carbohydrate formation. This stoichiometry is crucial for calculating carbon fixation efficiency and understanding the biochemical energetics of photosynthesis.

1. Single Correct Answer MCQ:
Which molecule is the immediate product of CO₂ fixation in the Calvin cycle?
1. Ribulose-1,5-bisphosphate
2. 3-Phosphoglycerate
3. Glyceraldehyde-3-phosphate
4. Fructose-1,6-bisphosphate
Explanation: Correct answer is 3-Phosphoglycerate (3-PGA). CO₂ is fixed by rubisco, combining with ribulose-1,5-bisphosphate to form an unstable 6-carbon intermediate, which immediately splits into two molecules of 3-PGA. These molecules are then used in the reduction phase to generate triose phosphate.

2. Single Correct Answer MCQ:
How many ATP molecules are consumed per CO₂ molecule during the reduction phase?
1. 1
2. 2
3. 3
4. 4
Explanation: Correct answer is 2 ATP. Each molecule of 3-PGA formed from CO₂ is phosphorylated by one ATP to produce 1,3-bisphosphoglycerate. Since one CO₂ produces two 3-PGA molecules, a total of 2 ATP molecules are consumed in the reduction phase for each CO₂ fixed.

3. Single Correct Answer MCQ:
How many NADPH molecules are required to reduce 3-PGA to triose phosphate per CO₂ molecule?
1. 1
2. 2
3. 3
4. 4
Explanation: Correct answer is 2 NADPH. Each 3-PGA molecule is reduced to G3P using one NADPH. Since one CO₂ produces two 3-PGA molecules, two NADPH molecules are needed for the reduction step, transferring high-energy electrons to form carbohydrate intermediates.

4. Single Correct Answer MCQ:
Which enzyme catalyzes the initial CO₂ fixation in the Calvin cycle?
1. Phosphoglycerate kinase
2. Rubisco
3. Glyceraldehyde-3-phosphate dehydrogenase
4. Aldolase
Explanation: Correct answer is Rubisco. Ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco) catalyzes the carboxylation of RuBP, forming two molecules of 3-PGA. Rubisco is the key enzyme linking the light-independent reactions to CO₂ assimilation.

5. Single Correct Answer MCQ:
The reduction of 3-PGA to G3P is driven by:
1. ATP only
2. NADPH only
3. Both ATP and NADPH
4. Light energy directly
Explanation: Correct answer is both ATP and NADPH. ATP phosphorylates 3-PGA to 1,3-bisphosphoglycerate, while NADPH provides electrons to reduce it to glyceraldehyde-3-phosphate. These photochemically generated intermediates are essential for the biosynthetic conversion of CO₂ into carbohydrates.

6. Single Correct Answer MCQ:
Which phase of the Calvin cycle follows the reduction phase?
1. Carboxylation
2. Regeneration of RuBP
3. Light-dependent reactions
4. Glycolysis
Explanation: Correct answer is regeneration of RuBP. After reduction of 3-PGA to G3P, a portion of G3P molecules is used to regenerate ribulose-1,5-bisphosphate (RuBP), ensuring continuation of the cycle. This phase consumes additional ATP but no NADPH.

7. Assertion-Reason MCQ:
Assertion (A): Two ATP and two NADPH are used to fix one CO₂ molecule into triose phosphate.
Reason (R): Each 3-PGA molecule formed consumes one ATP and one NADPH during reduction.
1. Both A and R are true and R explains A
2. Both A and R are true but R does not explain A
3. A is true, R is false
4. A is false, R is true
Explanation: Correct answer is option 1. Each CO₂ produces two 3-PGA molecules, each reduced using 1 ATP and 1 NADPH. Therefore, fixing one CO₂ requires 2 ATP and 2 NADPH. The reason accurately explains the stoichiometry of the reduction phase.

8. Matching Type MCQ:
Match molecule with function in reduction phase:
A. ATP – (i) Provides energy for phosphorylation
B. NADPH – (ii) Donates electrons
C. 3-PGA – (iii) Substrate for reduction
D. G3P – (iv) Product of reduction
1. A–i, B–ii, C–iii, D–iv
2. A–ii, B–i, C–iv, D–iii
3. A–iii, B–iv, C–ii, D–i
4. A–iv, B–iii, C–i, D–ii
Explanation: Correct answer is option 1. ATP provides phosphorylation energy, NADPH donates electrons, 3-PGA is reduced, and G3P is the product formed in the reduction phase of the Calvin cycle.

9. Fill in the Blanks MCQ:
The reduction of 3-PGA to G3P consumes ______ ATP and ______ NADPH per CO₂ molecule.
1. 1, 1
2. 2, 2
3. 2, 1
4. 1, 2
Explanation: Correct answer is 2 ATP and 2 NADPH. Each CO₂ produces two 3-PGA molecules. Phosphorylation of each 3-PGA uses 1 ATP and reduction uses 1 NADPH. Therefore, 2 ATP and 2 NADPH are consumed to produce one G3P molecule from one CO₂.

10. Choose the Correct Statements MCQ:
Statement I: Fixing one CO₂ into G3P requires 2 ATP.
Statement II: Fixing one CO₂ into G3P requires 2 NADPH.
1. Both Statement I and II are correct
2. Statement I is correct, II is incorrect
3. Statement I is incorrect, II is correct
4. Both Statement I and II are incorrect
Explanation: Correct answer is option 1. For each CO₂ fixed, two molecules of 3-PGA are produced. Each 3-PGA uses 1 ATP for phosphorylation and 1 NADPH for reduction. Therefore, 2 ATP and 2 NADPH are consumed, validating both statements as correct.

Topic: Essential Elements; Subtopic: Micronutrients in Photosynthesis

Keyword Definitions:

• Micronutrients: Essential elements required by plants in very small quantities for normal growth and metabolism.

• Photosynthesis: The process by which green plants use sunlight to synthesize food from carbon dioxide and water.

• Light Reaction: The phase of photosynthesis occurring in thylakoid membranes where light energy is converted into chemical energy (ATP and NADPH).

• Oxygen Evolution: The release of oxygen during the photolysis of water in photosystem II.

• Manganese and Chlorine: Essential micronutrients involved in the splitting of water molecules during photosynthesis.

Lead Question - 2022 (Abroad)
Which of the following pair of micronutrients would help in the light phase of photosynthesis to help in the reaction leading to oxygen evolution?
1. Zinc and Chlorine
2. Manganese and Molybdenum
3. Molybdenum and Iron
4. Manganese and Chlorine
Explanation: The light phase of photosynthesis involves the photolysis of water, which leads to oxygen evolution. The oxygen-evolving complex (OEC) of photosystem II requires manganese (Mn) and chlorine (Cl) ions as cofactors for splitting water molecules into protons, electrons, and oxygen. Hence, the correct answer is option 4 — Manganese and Chlorine.

1. Manganese plays an important role in:
1. Activation of nitrogenase enzyme
2. Splitting of water to release oxygen
3. Formation of chlorophyll pigment
4. Reduction of nitrates to ammonia
Explanation: Manganese (Mn) acts as a cofactor in the oxygen-evolving complex (OEC) of photosystem II. It facilitates the splitting of water molecules into protons, electrons, and oxygen during the light reaction of photosynthesis. Hence, the correct answer is option 2 — Splitting of water to release oxygen.

2. Chlorine deficiency in plants results in:
1. Reduced oxygen evolution and leaf wilting
2. Increased nitrate accumulation
3. Enhanced chlorophyll synthesis
4. Excessive transpiration
Explanation: Chlorine (Cl⁻) helps in maintaining osmotic balance and acts as an essential ion in the oxygen-evolving complex of photosystem II. Its deficiency reduces oxygen evolution, leading to wilting and chlorosis. Therefore, the correct answer is option 1 — Reduced oxygen evolution and leaf wilting.

3. The oxygen-evolving complex (OEC) is associated with:
1. Photosystem I
2. Photosystem II
3. Calvin cycle
4. Glycolysis
Explanation: The oxygen-evolving complex (OEC) or water-splitting complex is part of photosystem II, located on the inner surface of the thylakoid membrane. It catalyzes the photolysis of water to release oxygen, protons, and electrons. Hence, the correct answer is option 2 — Photosystem II.

4. Which of the following micronutrients is involved in nitrogen metabolism rather than oxygen evolution?
1. Manganese
2. Molybdenum
3. Chlorine
4. Iron
Explanation: Molybdenum (Mo) acts as a cofactor for nitrate reductase and nitrogenase enzymes, helping in nitrogen reduction and fixation. It is not directly involved in the oxygen-evolving complex of photosynthesis. Hence, the correct answer is option 2 — Molybdenum.

5. The splitting of water molecules during photosynthesis provides:
1. ATP
2. NADPH
3. Protons, electrons, and oxygen
4. Glucose and CO₂
Explanation: During the light reaction of photosynthesis, water is split by the oxygen-evolving complex in photosystem II into protons (H⁺), electrons (e⁻), and oxygen (O₂). This process provides electrons for photosynthetic electron transport and contributes to proton gradient formation. Hence, the correct answer is option 3.

6. Which pair of elements are directly required for photolysis of water in chloroplasts?
1. Mn and Cl
2. Fe and Mo
3. Zn and Cu
4. Mg and K
Explanation: The photolysis of water requires manganese (Mn) and chloride (Cl) ions as essential cofactors in the oxygen-evolving complex (OEC) of photosystem II. These elements help in the oxidation of water molecules, leading to oxygen evolution. Hence, the correct answer is option 1 — Mn and Cl.

7. Assertion (A): Manganese and Chlorine are required for oxygen evolution in plants.
Reason (R): They form part of the oxygen-evolving complex in photosystem II.
1. Both A and R are true, and R is the correct explanation of A
2. Both A and R are true, but R is not the correct explanation of A
3. A is true but R is false
4. A is false but R is true
Explanation: Manganese and Chlorine ions are essential for the oxygen-evolving complex (OEC) of photosystem II, which catalyzes the photolysis of water, releasing oxygen. Both statements are true, and the reason correctly explains the assertion. Hence, the correct answer is option 1.

8. Match the following:
A. Manganese — (i) Oxygen-evolving complex
B. Molybdenum — (ii) Nitrate reductase
C. Iron — (iii) Electron transport chain
1. A-(i), B-(ii), C-(iii)
2. A-(ii), B-(i), C-(iii)
3. A-(iii), B-(ii), C-(i)
4. A-(i), B-(iii), C-(ii)
Explanation: Manganese participates in oxygen evolution in PS II, Molybdenum in nitrate reduction, and Iron in electron transport during photosynthesis. Hence, the correct matching is A-(i), B-(ii), C-(iii), corresponding to option 1.

9. Fill in the blank:
The oxygen-evolving complex of photosystem II contains __________ ions essential for splitting of water.
1. Iron
2. Molybdenum
3. Manganese and Chlorine
4. Zinc and Copper
Explanation: The oxygen-evolving complex (OEC) consists of manganese and chloride ions that are critical for the photolysis of water molecules in photosystem II. These ions help stabilize the complex and enable the release of oxygen. Hence, the correct answer is option 3.

10. Choose the correct statements:
1. Manganese and Chlorine are involved in water splitting.
2. Iron is part of chlorophyll structure.
3. Molybdenum helps in nitrogen fixation.
4. Zinc acts as a cofactor for carbonic anhydrase.
Explanation: All four statements are scientifically correct. Manganese and Chlorine assist in oxygen evolution, Iron aids in electron transport, Molybdenum assists in nitrogen metabolism, and Zinc activates carbonic anhydrase for CO₂ fixation. Therefore, the correct answer is option 1, 2, 3, and 4 — all are correct.

Subtopic: CO2 Enrichment in Agriculture

• CO2 Enrichment: Increasing carbon dioxide concentration in the atmosphere to enhance photosynthesis and crop yield.

• Sugar Beet: A root crop rich in sucrose, cultivated for sugar production.

• Cabbage: Leafy vegetable belonging to Brassicaceae family, responds well to CO2 enrichment.

• Photosynthesis: Process by which plants convert CO2 and water into glucose and oxygen using sunlight.

• Crop Yield: Quantity of crop harvested per unit area.

• Tomatoes: Fruiting vegetable crop sensitive to CO2 enrichment for improved growth and yield.

• Wheat: Cereal crop; growth can be enhanced under higher CO2 conditions.

• Bell Pepper: Fruiting vegetable crop; yield responds to CO2-enriched environment.

• CO2 Fertigation: Technique of supplying CO2 to greenhouse crops for enhanced photosynthesis.

• Brassica Crops: Plants of mustard family, includes cabbage, respond to CO2 enrichment.

• Controlled Environment Agriculture: Using greenhouses or growth chambers to manipulate CO2, temperature, and light for crop productivity.

Lead Question - 2022 (Abroad)

Following crops have been extensively cultivated in CO2 rich atmosphere for higher yield:

1. Sugar beet and Cabbage

2. Carrots and Tomatoes

3. Wheat and Sugar beet

4. Tomatoes and Bell pepper

Explanation: Sugar beet and cabbage are among the crops that show significant increase in growth and yield under CO2-enriched atmospheres due to enhanced photosynthetic rates. These crops are commonly cultivated in controlled environment agriculture or greenhouses to utilize CO2 enrichment. Answer: Sugar beet and Cabbage. Answer: 1

Q1: Which photosynthetic pathway is more responsive to CO2 enrichment for increased yield?

1. C3 pathway

2. C4 pathway

3. CAM pathway

4. Both C4 and CAM

Explanation: C3 plants like sugar beet and cabbage show a higher increase in photosynthesis and yield under elevated CO2 conditions. C4 and CAM plants have mechanisms that already concentrate CO2, making them less responsive. Answer: C3 pathway. Answer: 1

Q2: Which greenhouse technique enhances crop yield using higher CO2?

1. Hydroponics

2. CO2 Fertigation

3. Mulching

4. Intercropping

Explanation: CO2 fertigation supplies additional carbon dioxide to greenhouse crops, boosting photosynthesis and yield. Hydroponics relates to soil-less cultivation, mulching reduces evaporation, and intercropping involves planting multiple crops together. Answer: CO2 Fertigation. Answer: 2

Q3: Which leafy vegetable responds well to CO2 enrichment?

1. Spinach

2. Cabbage

3. Lettuce

4. Beetroot

Explanation: Cabbage, a Brassica crop, shows enhanced growth and biomass accumulation under CO2-enriched conditions due to higher photosynthesis rates. Spinach and lettuce respond moderately, while beetroot is a root crop. Answer: Cabbage. Answer: 2

Q4: Elevated CO2 mainly enhances which process in plants?

1. Respiration

2. Transpiration

3. Photosynthesis

4. Germination

Explanation: Elevated CO2 increases the rate of photosynthesis in C3 plants by providing more substrate for carbon fixation, leading to higher biomass and yield. Respiration and transpiration are indirectly affected, while germination is not directly influenced. Answer: Photosynthesis. Answer: 3

Q5: Which crop is both a C3 plant and highly responsive to CO2 enrichment?

1. Maize

2. Sugar beet

3. Sorghum

4. Millet

Explanation: Sugar beet is a C3 plant that exhibits increased growth and yield under elevated CO2 due to enhanced photosynthetic efficiency. Maize, sorghum, and millet are C4 crops and show less response. Answer: Sugar beet. Answer: 2

Q6: CO2 enrichment is most commonly applied in which environment?

1. Open fields

2. Greenhouses

3. Hydroponics

4. Polyculture systems

Explanation: CO2 enrichment is typically applied in greenhouses where CO2 concentration can be controlled to boost photosynthesis and yield. Open fields cannot maintain elevated CO2 levels consistently. Hydroponics and polyculture are cultivation methods but not specifically CO2 enrichment environments. Answer: Greenhouses. Answer: 2

Q7: Assertion (A): CO2 enrichment increases yield of C3 crops.
Reason (R): Higher CO2 improves water use efficiency and photosynthetic rate in C3 plants.

1. A is correct but R is not correct

2. A is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: Elevated CO2 increases photosynthesis in C3 crops, improving biomass accumulation and yield. It also reduces stomatal opening, enhancing water use efficiency. Therefore, the reason explains the assertion correctly. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the crop with response to CO2 enrichment:

1. Sugar beet    A. High response
2. Wheat    B. Moderate response
3. Maize    C. Low response

1. 1-A, 2-B, 3-C

2. 1-B, 2-A, 3-C

3. 1-A, 2-C, 3-B

4. 1-C, 2-B, 3-A

Explanation: Sugar beet, a C3 crop, responds highly to CO2 enrichment. Wheat shows moderate increase, while maize, a C4 plant, responds minimally because its carbon concentrating mechanism reduces CO2 limitation. Correct match is 1-A, 2-B, 3-C. Answer: 1

Q9: Elevated CO2 reduces stomatal opening, thereby improving ______ in plants.

1. Photosynthetic rate

2. Water use efficiency

3. Respiration rate

4. Seed germination

Explanation: Elevated CO2 causes partial stomatal closure, reducing water loss and improving water use efficiency while simultaneously enhancing photosynthesis in C3 crops. Respiration and germination are not significantly affected. Answer: Water use efficiency. Answer: 2

Q10: Select the correct statements regarding CO2 enrichment:

1. Enhances photosynthesis in C3 plants

2. Improves water use efficiency

3. Used in greenhouses for higher yield

4. C4 plants show minimal response

Explanation: CO2 enrichment enhances photosynthesis and biomass accumulation in C3 crops, improves water use efficiency, and is applied in greenhouses for higher yield. C4 crops are less responsive due to their carbon-concentrating mechanism. All statements correctly describe CO2 enrichment effects. Answer: 1,2,3,4

Subtopic: Carbon Fixation in C3 and C4 Plants

• C3 Plants: Plants that fix CO2 through the Calvin cycle forming a 3-carbon compound (3-phosphoglycerate).

• C4 Plants: Plants that fix CO2 into a 4-carbon compound (oxaloacetate) before entering Calvin cycle, reducing photorespiration.

• Carbon Fixation: Conversion of inorganic CO2 into organic compounds during photosynthesis.

• Calvin Cycle: Light-independent reactions in chloroplasts that synthesize sugars using CO2.

• Photorespiration: Process where oxygen is consumed and CO2 released, reducing photosynthetic efficiency.

• Mesophyll Cells: Cells in leaves where initial CO2 fixation occurs in C4 plants.

• Bundle Sheath Cells: Specialized cells in C4 plants where Calvin cycle occurs.

• Efficiency: Rate of CO2 fixation per unit time under same conditions.

• PEP Carboxylase: Enzyme in C4 plants that fixes CO2 into oxaloacetate.

• Rubisco: Enzyme in Calvin cycle that fixes CO2 in both C3 and C4 plants.

• Photosynthetic Pathway: Biochemical steps by which plants convert CO2 into organic compounds.

Lead Question - 2022 (Abroad)

The ratio of carbon dioxide fixation between C4 plants and C3 plants is:

1. 2:1

2. 2:3

3. 1:1

4. 1:2

Explanation: C4 plants fix CO2 more efficiently than C3 plants due to their specialized mechanism that minimizes photorespiration. Under similar light and CO2 conditions, the rate of CO2 fixation in C4 plants is roughly twice that of C3 plants. Hence, the ratio of carbon dioxide fixation between C4 and C3 plants is 2:1. Answer: 1

Q1: Which enzyme initially fixes CO2 in C4 plants?

1. Rubisco

2. PEP Carboxylase

3. ATP Synthase

4. Hexokinase

Explanation: In C4 plants, CO2 is first fixed into oxaloacetate by PEP carboxylase in mesophyll cells, which reduces photorespiration. Rubisco later fixes CO2 in bundle sheath cells. ATP synthase and hexokinase are unrelated to initial CO2 fixation. Answer: PEP Carboxylase. Answer: 2

Q2: Where does the Calvin cycle occur in C4 plants?

1. Mesophyll cells

2. Bundle sheath cells

3. Stomata

4. Root hairs

Explanation: In C4 plants, CO2 is transported from mesophyll cells to bundle sheath cells where Rubisco fixes CO2 in the Calvin cycle. Mesophyll cells handle initial fixation, stomata are openings for gas exchange, and root hairs absorb water and minerals. Answer: Bundle sheath cells. Answer: 2

Q3: Main advantage of C4 pathway over C3 pathway is:

1. Higher water use efficiency

2. Reduced photorespiration

3. Better CO2 fixation under high temperature

4. All of the above

Explanation: C4 pathway reduces photorespiration, enhances water use efficiency, and allows better CO2 fixation under high temperature. These combined advantages make C4 plants more productive in tropical and subtropical climates. Answer: All of the above. Answer: 4

Q4: C3 plants predominantly use which photosynthetic pathway?

1. Hatch-Slack pathway

2. Calvin cycle

3. Cyclic photophosphorylation

4. Photorespiration pathway

Explanation: C3 plants fix CO2 directly through the Calvin cycle forming 3-phosphoglycerate. Hatch-Slack is specific to C4 plants, cyclic photophosphorylation generates ATP, and photorespiration is a wasteful process. Hence, Calvin cycle is the primary pathway. Answer: Calvin cycle. Answer: 2

Q5: In which cell type of C4 plants does PEP carboxylase operate?

1. Bundle sheath cells

2. Mesophyll cells

3. Guard cells

4. Parenchyma cells

Explanation: PEP carboxylase fixes CO2 into oxaloacetate in mesophyll cells of C4 plants, before transferring to bundle sheath cells for the Calvin cycle. Guard cells regulate stomata, and parenchyma cells have general metabolic roles. Answer: Mesophyll cells. Answer: 2

Q6: Which condition favors C4 photosynthesis over C3?

1. Low light intensity

2. High CO2 concentration

3. High temperature and drought

4. Low temperature

Explanation: C4 plants are more efficient than C3 under high temperature and drought because their mechanism minimizes photorespiration. Low light or low temperature favors C3 efficiency, and high CO2 reduces photorespiration in C3 plants. Answer: High temperature and drought. Answer: 3

Q7: Assertion (A): C4 plants have higher photosynthetic efficiency than C3 plants.
Reason (R): C4 plants concentrate CO2 around Rubisco, reducing photorespiration.

1. A is correct but R is not correct

2. A is not correct but R is correct

3. Both A and R are correct and R explains A

4. Both A and R are correct but R does not explain A

Explanation: C4 plants concentrate CO2 in bundle sheath cells around Rubisco, minimizing photorespiration and enhancing photosynthetic efficiency. Both assertion and reason are true, and the reason correctly explains the assertion. Answer: Both A and R are correct and R explains A. Answer: 3

Q8: Match the plant type with characteristic:

1. C3 Plant    A. Calvin cycle only
2. C4 Plant    B. CO2 first fixed into oxaloacetate
3. CAM Plant    C. Fixes CO2 at night, stores as malate

1. 1-A, 2-B, 3-C

2. 1-B, 2-A, 3-C

3. 1-C, 2-A, 3-B

4. 1-A, 2-C, 3-B

Explanation: C3 plants use Calvin cycle directly. C4 plants first fix CO2 into oxaloacetate via PEP carboxylase. CAM plants fix CO2 at night storing it as malate to minimize water loss. Correct matching is 1-A, 2-B, 3-C. Answer: 1

Q9: The enzyme responsible for fixing CO2 in Calvin cycle is ______.

1. PEP Carboxylase

2. Rubisco

3. ATP Synthase

4. NADP Reductase

Explanation: Rubisco catalyzes the fixation of CO2 into 3-phosphoglycerate during the Calvin cycle in both C3 and C4 plants. PEP carboxylase operates in C4 initial fixation, ATP synthase generates ATP, and NADP reductase participates in electron transport. Answer: Rubisco. Answer: 2

Q10: Select correct statements regarding C4 photosynthesis:

1. C4 plants reduce photorespiration

2. C4 plants have higher CO2 fixation under high temperature

3. PEP carboxylase fixes CO2 initially

4. CO2 is concentrated in bundle sheath cells for Calvin cycle

Explanation: C4 plants utilize PEP carboxylase for initial CO2 fixation, concentrate CO2 in bundle sheath cells, reduce photorespiration, and maintain high fixation rates under high temperature. All four statements accurately describe C4 photosynthesis. Answer: All of the above. Answer: 1,2,3,4

Topic: Light Reaction of Photosynthesis
Subtopic: Products of Light Reaction

Keyword Definitions:
- Light Reaction: The photochemical phase of photosynthesis where light energy is converted into chemical energy.
- ATP: Adenosine Triphosphate, an energy currency molecule formed during photophosphorylation.
- NADPH: Nicotinamide Adenine Dinucleotide Phosphate (reduced form), a reducing agent used in the Calvin cycle.
- Photolysis: The splitting of water by light energy, releasing O2, electrons, and protons.
- Photosystems: Complexes of pigments (PS I and PS II) that absorb light energy in chloroplasts.
- Electron Transport Chain: A series of carriers transferring electrons, producing ATP and NADPH.
- Photophosphorylation: Formation of ATP from ADP and inorganic phosphate using light energy.
- Oxygen Evolution: The release of O2 as a by-product of water splitting in photosynthesis.
- Chloroplast: Organelle where photosynthesis occurs in plant cells.
- Calvin Cycle: The dark phase using ATP and NADPH to fix CO2 into carbohydrates.

Lead Question - 2022 (Abroad):
The products of light reaction in photosynthesis are:
(1) ATP, NADPH and O2
(2) ATP, NADPH and O2 + H2O
(3) ATP, NADPH and H2O
(4) ATP, NADPH and CO2
Explanation: The correct answer is (1). The light reaction forms ATP and NADPH as energy molecules and releases O2 through photolysis of water. These products fuel the Calvin cycle to synthesize glucose during the dark reaction phase of photosynthesis.

1. Which pigment directly participates in the light reaction?
(a) Chlorophyll a
(b) Chlorophyll b
(c) Carotenoids
(d) Xanthophyll
Explanation: The correct answer is (a). Chlorophyll a acts as the primary pigment capturing light energy in the reaction center. It converts absorbed light energy into chemical energy that drives photochemical reactions in photosystems I and II.

2. The splitting of water molecule during light reaction releases:
(a) Hydrogen and Oxygen only
(b) Electrons, protons, and oxygen
(c) ATP and NADPH
(d) Glucose and oxygen
Explanation: The correct answer is (b). Water photolysis in photosystem II yields electrons, protons, and oxygen. Electrons replace those lost by chlorophyll, protons aid ATP synthesis, and oxygen is released as a by-product into the atmosphere.

3. Which photosystem is responsible for oxygen evolution?
(a) Photosystem I
(b) Photosystem II
(c) Both PSI and PSII
(d) Cytochrome complex
Explanation: The correct answer is (b). Photosystem II splits water molecules in the thylakoid lumen, releasing oxygen, protons, and electrons. This process is known as photolysis and is unique to PSII during the light-dependent reactions.

4. In non-cyclic photophosphorylation, electrons lost by PSII ultimately reduce:
(a) NADP+
(b) ATP
(c) O2
(d) H2O
Explanation: The correct answer is (a). In non-cyclic photophosphorylation, electrons from PSII are transferred to NADP+ via the electron transport chain, forming NADPH. This reducing power, along with ATP, supports CO2 fixation in the Calvin cycle.

5. Which of the following occurs in the stroma of chloroplast?
(a) Photolysis of water
(b) Photophosphorylation
(c) Calvin cycle
(d) Light absorption
Explanation: The correct answer is (c). The Calvin cycle, also called the dark reaction, takes place in the chloroplast stroma. It utilizes ATP and NADPH from the light reaction to convert carbon dioxide into glucose.

6. The oxygen released during photosynthesis comes from:
(a) CO2
(b) H2O
(c) Glucose
(d) NADPH
Explanation: The correct answer is (b). Oxygen released during photosynthesis originates from the photolysis of water molecules in Photosystem II. This process splits H2O into electrons, protons, and molecular oxygen, which diffuses out of the chloroplast.

7. Assertion-Reason:
Assertion (A): ATP and NADPH are produced during the light reaction.
Reason (R): These molecules are required in the Calvin cycle for carbon fixation.
(a) Both A and R are true, and R explains A
(b) Both A and R are true, but R does not explain A
(c) A is true, but R is false
(d) A is false, but R is true
Explanation: Option (a) is correct. ATP and NADPH generated in the light reaction provide energy and reducing power for carbon fixation in the Calvin cycle, linking both phases of photosynthesis efficiently.

8. Matching Type:
Match the following:
(a) Photosystem I (i) O2 evolution
(b) Photosystem II (ii) NADPH formation
(c) Photolysis (iii) Water splitting
(d) ATP synthase (iv) ATP formation
Options:
(1) a-ii, b-i, c-iii, d-iv
(2) a-iv, b-ii, c-i, d-iii
(3) a-i, b-iii, c-ii, d-iv
(4) a-ii, b-iv, c-i, d-iii
Explanation: The correct option is (1). Photosystem I forms NADPH, Photosystem II initiates O2 evolution, photolysis splits water, and ATP synthase produces ATP. These coordinated reactions sustain photosynthetic efficiency.

9. Fill in the Blank:
During photolysis, ______ is released as a by-product.
(a) Carbon dioxide
(b) Glucose
(c) Oxygen
(d) NADPH
Explanation: The correct answer is (c). Oxygen is released during photolysis in Photosystem II as water splits under light energy, providing electrons and protons for photosynthetic reactions.

10. Choose the Correct Statements:
1. Light reaction occurs in thylakoids.
2. O2 is released from photolysis of water.
3. ATP is produced in stroma.
4. NADPH is formed in Photosystem II.
(a) 1 and 2
(b) 1, 2, and 3
(c) 2, 3, and 4
(d) 1, 3, and 4
Explanation: Option (a) is correct. The light reaction occurs in thylakoids, releasing O2 from photolysis. ATP forms via ATP synthase, while NADPH forms in Photosystem I, not II.

Topic: C4 Pathway (Hatch and Slack Pathway)
Subtopic: Role of Bundle Sheath Cells and Kranz Anatomy

Keyword Definitions:

• Bundle Sheath Cells: Large cells surrounding vascular bundles in C4 plants, containing numerous chloroplasts for the Calvin cycle.

• Kranz Anatomy: Leaf anatomy in C4 plants with concentric arrangement of mesophyll and bundle sheath cells.

• Photorespiration: Wasteful process where oxygen is used instead of carbon dioxide, reducing photosynthetic efficiency.

• C4 Pathway: A photosynthetic adaptation minimizing photorespiration and increasing efficiency in high light and temperature.

• Calvin Cycle: The light-independent phase of photosynthesis occurring in the stroma or bundle sheath chloroplasts.

Lead Question (2022):
What is the role of large bundle sheath cells found around the vascular bundles in C4 plants:
(1) To increase the number of chloroplast for the operation of Calvin cycle
(2) To enable the plant to tolerate high temperature
(3) To protect the vascular tissue from high light intensity
(4) To provide the site for photorespiratory pathway

Explanation: In C4 plants, bundle sheath cells contain numerous chloroplasts that perform the Calvin cycle isolated from oxygen, reducing photorespiration. These cells concentrate CO₂ via the malate transport from mesophyll cells, enhancing photosynthetic efficiency. Hence, the correct answer is (1) To increase the number of chloroplast for the operation of Calvin cycle.

1. Guessed Question:
Which of the following is a characteristic feature of C4 plants?
(1) Presence of Kranz anatomy
(2) Absence of bundle sheath cells
(3) High rate of photorespiration
(4) Lack of PEP carboxylase enzyme

Explanation: C4 plants exhibit Kranz anatomy with mesophyll and bundle sheath cells functioning in coordination to reduce photorespiration. PEP carboxylase fixes CO₂ efficiently in mesophyll cells. Hence, the correct answer is (1) Presence of Kranz anatomy.

2. Guessed Question:
In C4 plants, the first stable compound formed during CO₂ fixation is:
(1) 3-phosphoglyceric acid
(2) Oxaloacetic acid
(3) Malic acid
(4) Pyruvic acid

Explanation: C4 plants initially fix CO₂ in mesophyll cells through PEP carboxylase forming oxaloacetic acid (OAA), a four-carbon compound. This compound is then reduced to malate or aspartate before entering bundle sheath cells. Hence, the correct answer is (2) Oxaloacetic acid.

3. Guessed Question:
PEP carboxylase is active in which part of C4 plant leaf?
(1) Bundle sheath cells
(2) Mesophyll cells
(3) Epidermal cells
(4) Guard cells

Explanation: PEP carboxylase is an enzyme located in mesophyll cells of C4 plants. It fixes atmospheric CO₂ into oxaloacetic acid before transport to bundle sheath cells, where the Calvin cycle occurs. Hence, the correct answer is (2) Mesophyll cells.

4. Guessed Question:
Which enzyme is responsible for the fixation of CO₂ in bundle sheath cells of C4 plants?
(1) RuBisCO
(2) PEP carboxylase
(3) Malate dehydrogenase
(4) Pyruvate kinase

Explanation: RuBisCO enzyme present in the chloroplasts of bundle sheath cells catalyzes CO₂ fixation during the Calvin cycle. This compartmentalization helps prevent photorespiration and enhances photosynthetic efficiency. Hence, the correct answer is (1) RuBisCO.

5. Guessed Question:
Which one of the following statements about C4 plants is correct?
(1) They show high photorespiration
(2) They perform Calvin cycle only in mesophyll cells
(3) They possess Kranz anatomy
(4) They grow best under low temperature and shade

Explanation: C4 plants possess Kranz anatomy that minimizes photorespiration and increases CO₂ fixation efficiency, especially under high temperature and light intensity. Hence, the correct answer is (3) They possess Kranz anatomy.

6. Guessed Question:
Which of the following pairs is correctly matched?
(1) PEP carboxylase – Bundle sheath cell
(2) RuBisCO – Mesophyll cell
(3) PEP carboxylase – Mesophyll cell
(4) RuBisCO – Epidermal cell

Explanation: In C4 plants, PEP carboxylase is located in mesophyll cells, and RuBisCO is found in bundle sheath cells. This separation of enzymes prevents photorespiration. Hence, the correct answer is (3) PEP carboxylase – Mesophyll cell.

7. Assertion-Reason Question:
Assertion (A): C4 plants have higher photosynthetic efficiency than C3 plants.
Reason (R): They lack photorespiration due to spatial separation of initial CO₂ fixation and Calvin cycle.
(1) Both A and R are true, and R explains A.
(2) Both A and R are true, but R does not explain A.
(3) A is true, R is false.
(4) A is false, R is true.

Explanation: C4 plants exhibit spatial separation between mesophyll and bundle sheath cells, reducing photorespiration and enhancing carbon fixation efficiency. Thus, both A and R are true, and R correctly explains A. Hence, the correct answer is (1).

8. Matching Type Question:
Match the following enzymes with their functions:
A. PEP carboxylase — (i) Fixes CO₂ in bundle sheath cells
B. RuBisCO — (ii) Fixes CO₂ in mesophyll cells
C. Malate dehydrogenase — (iii) Converts OAA to malate
Options:
(1) A–ii, B–i, C–iii
(2) A–iii, B–ii, C–i
(3) A–i, B–ii, C–iii
(4) A–ii, B–iii, C–i

Explanation: PEP carboxylase fixes CO₂ in mesophyll cells, RuBisCO fixes CO₂ in bundle sheath cells, and malate dehydrogenase converts oxaloacetate to malate. Hence, the correct answer is (1) A–ii, B–i, C–iii.

9. Fill in the Blanks:
In C4 plants, CO₂ is initially fixed into a ______ carbon compound called ______.
(1) Three, PGA
(2) Four, OAA
(3) Two, Acetate
(4) One, CO

Explanation: In C4 plants, CO₂ fixation in mesophyll cells produces a four-carbon compound called oxaloacetic acid (OAA), catalyzed by PEP carboxylase. Hence, the correct answer is (2) Four, OAA.

10. Choose the Correct Statements:
(a) C4 plants show Kranz anatomy.
(b) Photorespiration is negligible in C4 plants.
(c) PEP carboxylase is active in bundle sheath cells.
(d) Calvin cycle occurs in bundle sheath cells.
(1) (a), (b), and (d) only
(2) (a), (c), and (d) only
(3) (a) and (b) only
(4) (b), (c), and (d) only

Explanation: C4 plants exhibit Kranz anatomy, minimal photorespiration, and Calvin cycle activity in bundle sheath cells, while PEP carboxylase acts in mesophyll cells. Hence, the correct answer is (1) (a), (b), and (d) only.

Subtopic: Chemiosmosis and Energy Release

Keyword Definitions:

• ATP Synthesis: Formation of adenosine triphosphate from ADP and inorganic phosphate during cellular respiration or photosynthesis.

• Chemiosmosis: Movement of protons across a membrane, generating ATP through ATP synthase.

• Proton gradient: Difference in proton concentration across a membrane, driving ATP synthesis.

• NADP/NADPH: Nicotinamide adenine dinucleotide phosphate; NADP is reduced to NADPH during photosynthesis to carry electrons.

• Stroma: Fluid-filled space inside chloroplasts surrounding thylakoids.

• Electron gradient: Flow of electrons through an electron transport chain creating proton gradient.

• Membrane: Thylakoid membrane in chloroplasts where chemiosmosis occurs.

• Energy release: Conversion of chemical energy in proton gradients to ATP.

• Proton-motive force: Force generated by proton gradient that drives ATP synthase.

• ATP synthase: Enzyme that synthesizes ATP using energy from proton flow.

Lead Question (2022)
Which one of the following is not true regarding the release of energy during ATP synthesis through chemiosmosis ? It involves:
(1) Breakdown of electron gradient
(2) Movement of protons across the membrane to the stroma
(3) Reduction of NADP to NADPH2 on the stroma side of the membrane
(4) Breakdown of proton gradient

Explanation:
ATP synthesis via chemiosmosis depends on the proton gradient across the thylakoid membrane. Protons move to the stroma, releasing energy for ATP formation. Electron flow and proton gradient breakdown drive this process. Reduction of NADP to NADPH occurs separately in photosynthesis, not directly part of ATP energy release. Correct answer is (3).

1. Single Correct Answer MCQ:
Which membrane enzyme directly synthesizes ATP during chemiosmosis?
(1) NADP reductase
(2) ATP synthase
(3) Cytochrome b6f
(4) Rubisco

Explanation:
ATP synthase is the enzyme that produces ATP using energy from proton flow across the thylakoid membrane. NADP reductase reduces NADP to NADPH, cytochrome b6f transfers electrons, and Rubisco fixes CO2. Correct answer is (2).

2. Single Correct Answer MCQ:
The proton gradient for ATP synthesis is established by:
(1) Proton pumps in mitochondrial matrix
(2) Electron transport chain in thylakoid membrane
(3) Cytoplasmic diffusion
(4) Stroma enzymes

Explanation:
The electron transport chain in the thylakoid membrane pumps protons into the lumen, creating a gradient. This gradient drives ATP synthesis. Cytoplasmic diffusion or stroma enzymes do not establish the proton gradient. Correct answer is (2).

3. Single Correct Answer MCQ:
Energy for ATP synthesis is released by:
(1) Electron absorption
(2) Proton flow down gradient
(3) Water splitting
(4) CO2 fixation

Explanation:
Protons flow down their gradient through ATP synthase, releasing energy used to synthesize ATP. Electron absorption initiates proton pumping, water splitting provides electrons, and CO2 fixation is part of Calvin cycle, not ATP energy release. Correct answer is (2).

4. Single Correct Answer MCQ:
The side of the membrane where protons accumulate is:
(1) Stroma
(2) Thylakoid lumen
(3) Cytoplasm
(4) Mitochondrial matrix

Explanation:
Protons accumulate inside the thylakoid lumen, creating a high concentration. ATP synthase allows them to move to the stroma. Cytoplasm and mitochondrial matrix are not relevant to chloroplast chemiosmosis. Correct answer is (2).

5. Single Correct Answer MCQ:
Which molecule carries electrons in the light reactions?
(1) NADPH
(2) NADP+
(3) FAD
(4) Cytochrome b6f

Explanation:
NADP+ accepts electrons and is reduced to NADPH in light reactions. Cytochrome b6f transfers electrons but does not carry them long-term. FAD is involved in respiration, not photosynthesis. Correct answer is (2).

6. Single Correct Answer MCQ:
Chemiosmosis in chloroplasts primarily occurs in:
(1) Outer membrane
(2) Thylakoid membrane
(3) Stroma
(4) Cytoplasm

Explanation:
Chemiosmosis occurs across the thylakoid membrane where protons flow from lumen to stroma through ATP synthase, releasing energy. Outer membrane, stroma, or cytoplasm are not sites of chemiosmotic ATP synthesis. Correct answer is (2).

7. Assertion-Reason MCQ:
Assertion (A): ATP synthesis requires proton movement.
Reason (R): Electron transport generates proton gradient across thylakoid membrane.
Options:
(1) Both A and R correct, R explains A
(2) A correct, R incorrect
(3) A incorrect, R correct
(4) Both A and R incorrect

Explanation:
ATP synthesis depends on protons moving through ATP synthase, which is driven by the gradient created by electron transport. Both statements are correct and R explains A. Correct answer is (1).

8. Matching Type MCQ:
Match molecule with its role:
A. NADP+ — 1. Electron carrier
B. ATP synthase — 2. ATP production
C. Proton gradient — 3. Energy source
D. Water — 4. Electron donor
Options:
(1) A–1, B–2, C–3, D–4
(2) A–2, B–1, C–4, D–3
(3) A–1, B–3, C–2, D–4
(4) A–3, B–2, C–1, D–4

Explanation:
NADP+ is an electron carrier (1), ATP synthase produces ATP (2), proton gradient provides energy (3), and water donates electrons in photolysis (4). Correct answer is (1).

9. Fill in the Blanks MCQ:
Protons move from thylakoid lumen to ________ during ATP synthesis.
(1) Cytoplasm
(2) Stroma
(3) Matrix
(4) Outer membrane

Explanation:
Protons flow from the thylakoid lumen to the stroma through ATP synthase, releasing energy to produce ATP. Cytoplasm, matrix, or outer membrane are incorrect. Correct answer is (2).

10. Choose the correct statements MCQ:
(a) ATP is synthesized using proton-motive force
(b) NADPH production is part of ATP chemiosmosis
(c) Electron transport generates proton gradient
(d) Protons move from lumen to stroma through ATP synthase
Options:
(1) a,

Topic: C4 Pathway

Subtopic: Carbon Dioxide Fixation and Enzymatic Distribution

Keyword Definitions:

• Phosphoenolpyruvate (PEP): A 3-carbon compound that acts as the primary CO₂ acceptor in C4 plants.

• RuBisCo: Ribulose-1,5-bisphosphate carboxylase/oxygenase, an enzyme responsible for CO₂ fixation in the Calvin cycle.

• Mesophyll Cells: Photosynthetic cells present in C4 plants where the initial fixation of CO₂ occurs.

• Bundle Sheath Cells: Cells surrounding vascular bundles, where the Calvin cycle operates in C4 plants.

Lead Question (2022):

Given below are two statements:

Statement I: The primary CO₂ acceptor in C4 plants is phosphoenolpyruvate and is found in the mesophyll cells.
Statement II: Mesophyll cells of C4 plants lack RuBisCo enzyme.
In the light of the above statements, choose the correct answer from the options given below:

(1) Both Statement I and Statement II are incorrect
(2) Statement I is correct but Statement II is incorrect
(3) Statement I is incorrect but Statement II is correct
(4) Both, Statement I and Statement II are correct

Explanation (Answer: 4)
In C4 plants, phosphoenolpyruvate (PEP) acts as the first CO₂ acceptor within mesophyll cells, forming oxaloacetate. RuBisCo enzyme is restricted to bundle sheath cells and absent in mesophyll cells, reducing photorespiration. Hence, both statements are correct, describing spatial separation of CO₂ fixation and the Calvin cycle.

1. Which enzyme fixes CO₂ in C4 plants?

(1) RuBisCo
(2) PEP carboxylase
(3) Hexokinase
(4) Pyruvate kinase

Explanation (Answer: 2)
PEP carboxylase catalyzes the first CO₂ fixation step in C4 plants, converting phosphoenolpyruvate into oxaloacetate in mesophyll cells. This spatial separation reduces photorespiration, making photosynthesis more efficient under high temperature and light conditions.

2. In which part of C4 plants does the Calvin cycle occur?

(1) Mesophyll cells
(2) Epidermal cells
(3) Bundle sheath cells
(4) Guard cells

Explanation (Answer: 3)
The Calvin cycle occurs exclusively in the bundle sheath cells of C4 plants. These cells contain RuBisCo enzyme, which fixes CO₂ released from malate. This compartmentalization minimizes photorespiration and enhances photosynthetic efficiency.

3. The first stable product of C4 cycle is:

(1) Malate
(2) Oxaloacetate
(3) Pyruvate
(4) PGA

Explanation (Answer: 2)
The first stable product of the C4 pathway is oxaloacetate, a four-carbon compound formed by carboxylation of phosphoenolpyruvate (PEP) by PEP carboxylase in mesophyll cells. It is later converted to malate or aspartate for CO₂ transfer to bundle sheath cells.

4. C4 plants are more efficient because:

(1) They require less ATP
(2) They minimize photorespiration
(3) They fix CO₂ directly with RuBisCo
(4) They lack bundle sheath cells

Explanation (Answer: 2)
C4 plants minimize photorespiration through spatial separation of initial CO₂ fixation and the Calvin cycle. CO₂ is first fixed by PEP carboxylase in mesophyll cells, then concentrated in bundle sheath cells where RuBisCo operates efficiently.

5. Which of the following is a C4 plant?

(1) Wheat
(2) Rice
(3) Maize
(4) Potato

Explanation (Answer: 3)
Maize (corn) is a C4 plant exhibiting Kranz anatomy. Its mesophyll and bundle sheath cells coordinate CO₂ fixation through PEP carboxylase and RuBisCo, respectively, reducing photorespiration and improving photosynthetic efficiency in tropical climates.

6. What is Kranz anatomy?

(1) Arrangement of guard cells
(2) Specialized leaf anatomy in C4 plants
(3) Root modification
(4) Chloroplast distribution in epidermis

Explanation (Answer: 2)
Kranz anatomy refers to the specialized leaf anatomy in C4 plants where mesophyll cells surround bundle sheath cells. This structure facilitates efficient carbon fixation and minimizes photorespiration by spatial separation of PEP carboxylase and RuBisCo enzymes.

7. Assertion-Reason Type:

Assertion (A): C4 plants are more efficient in hot climates.
Reason (R): They possess a mechanism to concentrate CO₂ around RuBisCo.
(1) Both A and R are true, and R is the correct explanation of A
(2) Both A and R are true, but R is not the correct explanation of A
(3) A is true, R is false
(4) A is false, R is true

Explanation (Answer: 1)
C4 plants concentrate CO₂ around RuBisCo, preventing oxygenase activity and reducing photorespiration. This adaptation makes them highly efficient in hot, dry climates with high light intensity.

8. Matching Type:

Match the following:
A. PEP carboxylase — (i) Bundle sheath cell
B. RuBisCo — (ii) Mesophyll cell
C. Calvin cycle — (iii) C4 plants
(1) A–ii, B–i, C–iii
(2) A–i, B–ii, C–iii
(3) A–iii, B–i, C–ii
(4) A–ii, B–iii, C–i

Explanation (Answer: 1)
PEP carboxylase acts in mesophyll cells; RuBisCo functions in bundle sheath cells where the Calvin cycle occurs. This coordination defines the spatial organization in C4 plants.

9. Fill in the Blanks:

In C4 photosynthesis, the Calvin cycle occurs in ________ cells.

(1) Mesophyll
(2) Bundle sheath
(3) Epidermal
(4) Guard

Explanation (Answer: 2)
The Calvin cycle in C4 plants occurs in bundle sheath cells containing RuBisCo, ensuring efficient CO₂ fixation and low photorespiration rates.

10. Choose the Correct Statements:

(1) RuBisCo is present in both mesophyll and bundle sheath cells of C4 plants.
(2) PEP carboxylase acts only in mesophyll cells.
(3) C4 plants perform photorespiration at high rates.
(4) Calvin cycle occurs in mesophyll cells of C4 plants.

Explanation (Answer: 2)
PEP carboxylase acts only in mesophyll cells for initial CO₂ fixation in C4 plants. RuBisCo operates in bundle sheath cells, leading to reduced photorespiration and improved photosynthetic efficiency.

Topic: Electron Transport Chain

Subtopic: Oxidative Phosphorylation

• Electron Transport Chain (ETC): Series of protein complexes transferring electrons to produce ATP.

• NADH: Nicotinamide adenine dinucleotide, electron donor in respiration.

• FADH2: Flavin adenine dinucleotide, electron carrier in ETC.

• ATP Synthase (Complex V): Enzyme synthesizing ATP using proton gradient.

• Proton Gradient: Difference in proton concentration across inner mitochondrial membrane.

• Oxidation-Reduction Reactions: Reactions transferring electrons, generating energy.

• Aerobic Respiration: Energy-producing process using oxygen as terminal electron acceptor.

• Terminal Stage: Final step in ETC where oxygen accepts electrons forming water.

• Oxidative Phosphorylation: ATP formation coupled to electron transfer through ETC.

• ATP Yield: Number of ATP molecules generated per NADH or FADH2.

• Mitochondrial Inner Membrane: Location of ETC and ATP synthase.

Lead Question - 2021

Which of the following statements is incorrect?

1. In ETC, one molecule of NADH + H+ gives rise to 2 ATP molecules, and one FADH2 gives rise to 3 ATP molecules.
Options:
A. Correct statement
B. Incorrect statement
C. Partially correct
D. Cannot be determined

Explanation: This statement is incorrect because in oxidative phosphorylation, one molecule of NADH produces approximately 3 ATP molecules, while FADH2 yields about 2 ATP molecules. The reverse given in the statement is a common misconception. Answer: Incorrect statement.

2. ATP is synthesized through complex V.
Options:
A. True
B. False
C. Partially true
D. Cannot say

Explanation: ATP synthesis occurs through ATP synthase (complex V) in the inner mitochondrial membrane, utilizing the proton gradient generated by ETC. It couples proton flow with phosphorylation of ADP to ATP, forming the primary energy currency for cellular processes. Answer: True.

3. Oxidation-reduction reactions produce proton gradient in respiration.
Options:
A. True
B. False
C. Only in anaerobic respiration
D. Only in cytoplasm

Explanation: During respiration, oxidation-reduction reactions in ETC transfer electrons, pumping protons across the inner mitochondrial membrane, generating a proton gradient. This gradient is essential for ATP synthesis via chemiosmosis. Answer: True.

4. During aerobic respiration, role of oxygen is limited to the terminal stage.
Options:
A. True
B. False
C. Oxygen acts throughout
D. Only in glycolysis

Explanation: Oxygen acts as the terminal electron acceptor at the end of the ETC, forming water. Its role is crucial only in this terminal stage of aerobic respiration, enabling continued electron flow and maintenance of the proton gradient for ATP synthesis. Answer: True.

5. The main site of ETC and oxidative phosphorylation is:
Options:
A. Cytoplasm
B. Mitochondrial inner membrane
C. Nucleus
D. Lysosome