This section explores the advanced molecular and biochemical aspects of the light and dark reactions of photosynthesis. It focuses on energy conversion, electron transport regulation, and efficiency of carbon fixation , making it suitable for advanced Class 12 students, NEET aspirants aiming for high scores, and undergraduate learners .
In this section, you will study:
Detailed organization of photosystems and light-harvesting complexes
Mechanism of non-cyclic and cyclic photophosphorylation
Chemiosmotic hypothesis and ATP synthesis
Regulation of electron transport and photoprotection mechanisms
Detailed enzymatic steps of the Calvin cycle
Regulation of RuBisCO activity and photorespiration
Interaction between light and dark reactions
Experimental evidences and advanced NCERT-based interpretations
The content is designed to strengthen conceptual depth , improve reasoning-based and assertion–reason questions , and help students confidently handle high-difficulty NEET and undergraduate-level questions .
Develop a deeper understanding of photosynthesis by linking molecular mechanisms with energy efficiency and plant productivity.
Q. How does the concentration of carbon dioxide affect the rate of photosynthesis?
A.
Increases rate
B.
Decreases rate
C.
No effect
D.
Only affects light reactions
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Solution
Increasing the concentration of carbon dioxide generally increases the rate of photosynthesis up to a certain point.
Correct Answer:
A
— Increases rate
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Q. In which part of the chloroplast do the light reactions occur?
A.
Stroma
B.
Thylakoid membranes
C.
Outer membrane
D.
Inner membrane
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Solution
The light reactions of photosynthesis occur in the thylakoid membranes of the chloroplast.
Correct Answer:
B
— Thylakoid membranes
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Q. In which part of the chloroplast do the light-dependent reactions occur?
A.
Stroma
B.
Thylakoid membranes
C.
Outer membrane
D.
Inner membrane
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Solution
The light-dependent reactions occur in the thylakoid membranes of the chloroplast.
Correct Answer:
B
— Thylakoid membranes
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Q. What is photolysis in the context of photosynthesis?
A.
Splitting of water molecules
B.
Formation of glucose
C.
Absorption of light
D.
Release of oxygen
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Solution
Photolysis refers to the splitting of water molecules during the light-dependent reactions.
Correct Answer:
A
— Splitting of water molecules
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Q. What is produced as a byproduct of the light-dependent reactions of photosynthesis?
A.
Glucose
B.
Oxygen
C.
NADPH
D.
ATP
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Solution
Oxygen is produced as a byproduct of the light-dependent reactions.
Correct Answer:
B
— Oxygen
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Q. What is produced during the light-dependent reactions of photosynthesis?
A.
Glucose
B.
Oxygen
C.
NADPH
D.
Both B and C
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Solution
Oxygen and NADPH are produced during the light-dependent reactions.
Correct Answer:
D
— Both B and C
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Q. What is the main purpose of the Calvin cycle in photosynthesis?
A.
To produce ATP
B.
To fix carbon dioxide
C.
To generate oxygen
D.
To absorb light energy
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Solution
The main purpose of the Calvin cycle is to fix carbon dioxide into organic molecules.
Correct Answer:
B
— To fix carbon dioxide
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Q. What is the primary pigment involved in photosynthesis that absorbs light energy?
A.
Chlorophyll a
B.
Carotenoids
C.
Xanthophylls
D.
Chlorophyll b
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Solution
Chlorophyll a is the main pigment that absorbs light energy for photosynthesis.
Correct Answer:
A
— Chlorophyll a
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Q. What is the role of ATP and NADPH in the Calvin cycle?
A.
Energy and reducing power
B.
Oxygen production
C.
Carbon fixation
D.
Light absorption
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Solution
ATP provides energy and NADPH provides reducing power for the Calvin cycle.
Correct Answer:
A
— Energy and reducing power
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Q. What is the role of ATP in the light-independent reactions?
A.
Energy source
B.
Electron carrier
C.
Carbon source
D.
None of the above
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Solution
ATP serves as the energy source for the light-independent reactions (Calvin cycle).
Correct Answer:
A
— Energy source
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Q. What is the role of NADPH in photosynthesis?
A.
Energy storage
B.
Electron transport
C.
Carbon fixation
D.
Light absorption
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Solution
NADPH serves as an electron carrier in the light-independent reactions of photosynthesis.
Correct Answer:
B
— Electron transport
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Q. What is the significance of the Z-scheme in photosynthesis?
A.
It describes the Calvin cycle
B.
It illustrates electron transport
C.
It shows light absorption
D.
It explains water splitting
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Solution
The Z-scheme illustrates the flow of electrons through the photosystems during light reactions.
Correct Answer:
B
— It illustrates electron transport
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Q. Which enzyme catalyzes the first step of the Calvin cycle?
A.
Rubisco
B.
ATP synthase
C.
NADP+ reductase
D.
Phosphofructokinase
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Solution
Rubisco catalyzes the first step of the Calvin cycle by fixing carbon dioxide.
Correct Answer:
A
— Rubisco
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Q. Which factor does NOT affect the rate of photosynthesis?
A.
Light intensity
B.
Carbon dioxide concentration
C.
Soil pH
D.
Temperature
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Solution
Soil pH does not directly affect the rate of photosynthesis.
Correct Answer:
C
— Soil pH
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Q. Which factor does NOT directly affect the rate of photosynthesis?
A.
Light intensity
B.
Temperature
C.
Soil pH
D.
Carbon dioxide concentration
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Solution
Soil pH does not directly affect the rate of photosynthesis; it affects plant health indirectly.
Correct Answer:
C
— Soil pH
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Q. Which molecule acts as the primary electron donor in the light reactions?
A.
Water
B.
NADP+
C.
Glucose
D.
RuBP
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Solution
Water acts as the primary electron donor in the light reactions, providing electrons.
Correct Answer:
A
— Water
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Q. Which of the following factors can limit the rate of photosynthesis?
A.
Light intensity
B.
Carbon dioxide concentration
C.
Temperature
D.
All of the above
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Solution
All of the above factors can limit the rate of photosynthesis.
Correct Answer:
D
— All of the above
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Q. Which of the following is a product of the light reactions that is used in the Calvin cycle?
A.
Oxygen
B.
Glucose
C.
NADPH
D.
Carbon dioxide
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Solution
NADPH is a product of the light reactions that is used in the Calvin cycle.
Correct Answer:
C
— NADPH
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Q. Which of the following is a product of the light-dependent reactions that is used in the Calvin cycle?
A.
Oxygen
B.
NADPH
C.
Glucose
D.
RuBP
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Solution
NADPH is a product of the light-dependent reactions that is used in the Calvin cycle.
Correct Answer:
B
— NADPH
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Q. Which of the following is NOT a product of the light reactions?
A.
ATP
B.
NADPH
C.
Glucose
D.
Oxygen
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Solution
Glucose is not produced during the light reactions; it is synthesized in the Calvin cycle.
Correct Answer:
C
— Glucose
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