Photosynthesis: Light and Dark Reactions focuses on the two main stages of photosynthesis that convert light energy into chemical energy in plants. This category explains the mechanism, sequence of reactions, and energy transformations involved, making it suitable for school students (Classes 11–12) , NEET aspirants , and undergraduate learners .
In this section, you will study:
Light reaction and its site in the thylakoid membrane
Role of photosystems I and II
Photolysis of water and oxygen evolution
Electron transport chain and photophosphorylation
Dark reaction and the Calvin cycle
Role of ATP and NADPH in carbon fixation
Regulation and efficiency of photosynthetic reactions
NCERT-based explanations, diagrams, flowcharts, MCQs, and exam-oriented questions
The content is structured to build step-by-step conceptual clarity , strengthen process-based understanding , and help students perform confidently in school examinations, NEET, and undergraduate assessments .
Develop a strong understanding of how light energy is captured and converted into organic molecules through coordinated light and dark reactions.
Q. During which phase of photosynthesis is carbon dioxide incorporated into organic molecules?
A.
Light reactions
B.
Calvin cycle
C.
Photorespiration
D.
Electron transport chain
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Solution
Carbon dioxide is incorporated into organic molecules during the Calvin cycle.
Correct Answer:
B
— Calvin cycle
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Q. In which part of the chloroplast do the light reactions of photosynthesis occur?
A.
Stroma
B.
Thylakoid membranes
C.
Cytoplasm
D.
Outer membrane
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Solution
The light reactions occur in the thylakoid membranes of the chloroplast.
Correct Answer:
B
— Thylakoid membranes
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Q. In which phase of photosynthesis is carbon dioxide utilized?
A.
Light reactions
B.
Calvin cycle
C.
Photorespiration
D.
Electron transport chain
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Solution
Carbon dioxide is utilized in the Calvin cycle during photosynthesis.
Correct Answer:
B
— Calvin cycle
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Q. What is produced during the light reactions of photosynthesis?
A.
Glucose
B.
Oxygen
C.
NADPH
D.
Both Oxygen and NADPH
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Solution
Both oxygen and NADPH are produced during the light reactions.
Correct Answer:
D
— Both Oxygen and NADPH
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Q. What is the main energy currency produced during the light reactions?
A.
NADPH
B.
FADH2
C.
ATP
D.
Glucose
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Solution
ATP is the main energy currency produced during the light reactions of photosynthesis.
Correct Answer:
C
— ATP
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Q. What is the main function of the light reactions in photosynthesis?
A.
To produce glucose
B.
To convert light energy into chemical energy
C.
To release carbon dioxide
D.
To absorb water
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Solution
The main function of the light reactions is to convert light energy into chemical energy in the form of ATP and NADPH.
Correct Answer:
B
— To convert light energy into chemical energy
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Q. What is the main function of the light reactions?
A.
To produce glucose
B.
To convert solar energy to chemical energy
C.
To release carbon dioxide
D.
To synthesize proteins
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Solution
The main function of the light reactions is to convert solar energy into chemical energy in the form of ATP and NADPH.
Correct Answer:
B
— To convert solar energy to chemical energy
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Q. What is the main function of the thylakoid membrane?
A.
Storage of glucose
B.
Light absorption
C.
Carbon fixation
D.
Water splitting
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Solution
The thylakoid membrane's main function is to absorb light energy for photosynthesis.
Correct Answer:
B
— Light absorption
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Q. What is the primary pigment involved in photosynthesis?
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 role does water play in the light reactions of photosynthesis?
A.
Source of carbon
B.
Source of electrons
C.
Source of ATP
D.
Source of glucose
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Solution
Water acts as a source of electrons in the light reactions, which are used to replace those lost by chlorophyll.
Correct Answer:
B
— Source of electrons
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Q. Which enzyme is responsible for carbon fixation in the Calvin cycle?
A.
Rubisco
B.
ATP synthase
C.
NADP+ reductase
D.
Phosphofructokinase
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Solution
Rubisco is the enzyme that catalyzes the fixation of carbon dioxide in the Calvin cycle.
Correct Answer:
A
— Rubisco
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Q. Which enzyme is responsible for fixing carbon dioxide in the Calvin cycle?
A.
Rubisco
B.
ATP synthase
C.
NADP+ reductase
D.
Phosphofructokinase
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Solution
Rubisco is the enzyme that catalyzes the fixation of carbon dioxide in the Calvin cycle.
Correct Answer:
A
— Rubisco
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Q. Which gas is a byproduct of the light reactions?
A.
Carbon dioxide
B.
Nitrogen
C.
Oxygen
D.
Methane
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Solution
Oxygen is released as a byproduct of the light reactions of photosynthesis.
Correct Answer:
C
— Oxygen
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Q. Which molecule acts as an electron carrier in the light reactions?
A.
ATP
B.
NADPH
C.
FADH2
D.
RuBP
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Solution
NADPH acts as an electron carrier in the light reactions.
Correct Answer:
B
— NADPH
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Q. Which molecule acts as the primary energy carrier in the dark reactions?
A.
ATP
B.
NADPH
C.
Glucose
D.
RuBP
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Solution
ATP is the primary energy carrier used in the dark reactions (Calvin cycle).
Correct Answer:
A
— ATP
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Q. Which molecule acts as the primary energy carrier in the light reactions?
A.
ATP
B.
NADPH
C.
Glucose
D.
RuBP
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Solution
ATP is the primary energy carrier produced during the light reactions.
Correct Answer:
A
— ATP
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Q. Which of the following is NOT a product of the light-dependent reactions?
A.
ATP
B.
NADPH
C.
Oxygen
D.
Glucose
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Solution
Glucose is not produced in the light-dependent reactions; it is produced in the Calvin cycle.
Correct Answer:
D
— Glucose
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