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12th Biology MCQ PDF - NCERT Based
NCERT Based MCQ with Explanation:
1. Which molecule is the primary electron donor in the light reactions of photosynthesis?
A) Water
B) NADPH
C) Glucose
D) Carbon dioxide
Explanation: In the light-dependent reactions of photosynthesis, water acts as the primary electron donor. When water molecules are split by an enzyme in Photosystem II, they release electrons, hydrogen ions (protons), and oxygen. These electrons are then used in the electron transport chain to generate energy-rich molecules like ATP and NADPH.
2. Which process produces oxygen as a byproduct during photosynthesis?
A) Calvin cycle
B) Glycolysis
C) Light-dependent reactions
D) Krebs cycle
Explanation: Oxygen is released as a byproduct during the light-dependent reactions when water molecules are split in Photosystem II. This process, known as photolysis, separates water into oxygen, protons, and electrons. The oxygen is then released into the atmosphere, which is essential for aerobic organisms.
3. In which part of the chloroplast does the Calvin cycle occur?
A) Thylakoid membrane
B) Grana
C) Stroma
D) Outer membrane
Explanation: The Calvin cycle, also known as the light-independent reactions, takes place in the stroma of the chloroplast. Here, carbon dioxide is fixed and converted into glucose using ATP and NADPH produced during the light-dependent reactions.
4. Which scientist discovered that oxygen is released by plants during photosynthesis?
A) Melvin Calvin
B) Joseph Priestley
C) Julius von Sachs
D) Jan Ingenhousz
Explanation: Joseph Priestley conducted experiments that demonstrated that plants could restore "damaged" air, allowing a candle to burn longer in a closed container. He discovered oxygen in 1774, recognizing its importance in plant processes.
5. Which pigment is directly responsible for converting light energy into chemical energy?
A) Chlorophyll a
B) Chlorophyll b
C) Xanthophyll
D) Carotenoids
Explanation: Chlorophyll a is the primary pigment that directly captures light energy and converts it into chemical energy in photosynthesis. Other pigments, such as chlorophyll b and carotenoids, act as accessory pigments that transfer the absorbed energy to chlorophyll a.
6. What is the primary function of accessory pigments in photosynthesis?
A) Absorb CO₂
B) Absorb additional wavelengths of light
C) Produce oxygen
D) Convert ATP to ADP
Explanation: Accessory pigments like chlorophyll b, carotenoids, and xanthophylls absorb light at different wavelengths than chlorophyll a, which broadens the spectrum of light a plant can use. They transfer this energy to chlorophyll a, helping optimize photosynthesis.
7. What is the main product of the Calvin cycle?
A) Oxygen
B) ATP
C) Glucose
D) NADPH
Explanation: The Calvin cycle fixes carbon dioxide and produces glucose as the primary product. The cycle uses ATP and NADPH from the light-dependent reactions to form this carbohydrate, which provides energy for plant growth.
8. Which molecule is regenerated in the Calvin cycle, allowing it to continue?
A) NADPH
B) RuBP
C) Glucose
D) ATP
Explanation: Ribulose-1,5-bisphosphate (RuBP) is regenerated at the end of the Calvin cycle, allowing the cycle to continue with additional rounds of carbon fixation. RuBP is the molecule to which CO₂ is initially fixed by the enzyme RuBisCO.
9. In the Z-scheme, electrons are passed from Photosystem II to Photosystem I through a series of proteins. What is this process called?
A) Cyclic photophosphorylation
B) Non-cyclic photophosphorylation
C) Chemiosmosis
D) Calvin cycle
Explanation: In non-cyclic photophosphorylation, electrons move from water through Photosystem II and Photosystem I to eventually reduce NADP+ to NADPH. This electron flow creates an energy gradient used to synthesize ATP and does not return the electrons to the original donor.
10. Which enzyme is responsible for producing ATP in the light-dependent reactions?
A) RuBisCO
B) ATP synthase
C) PEP carboxylase
D) NADP reductase
Explanation: ATP synthase, located in the thylakoid membrane, synthesizes ATP using the proton gradient established across the membrane during the light-dependent reactions. The flow of protons through ATP synthase provides the energy required to convert ADP to ATP.
Science MCQ, Class 10th, Chapter-11, Electricity11. What is the first stable compound formed in the Calvin cycle when CO₂ is fixed?
A) Oxaloacetic acid
B) 3-phosphoglycerate (3-PGA)
C) Malate
D) Pyruvate
Explanation: The enzyme RuBisCO fixes CO₂ by attaching it to RuBP, resulting in an unstable 6-carbon compound that quickly splits into two molecules of 3-phosphoglycerate (3-PGA), a stable 3-carbon compound.
12. In C4 plants, what is the first stable compound formed in carbon fixation?
A) Oxaloacetic acid (OAA)
B) 3-phosphoglycerate (3-PGA)
C) Malic acid
D) Pyruvate
Explanation: In C4 plants, the enzyme PEP carboxylase fixes CO₂ into a 4-carbon compound, oxaloacetic acid (OAA), in the mesophyll cells. This compound is then transported to bundle sheath cells, where CO₂ is released for fixation by the Calvin cycle.
13. What is the main advantage of the C4 pathway in plants?
A) Reduced oxygen production
B) Increased rate of water absorption
C) Reduced photorespiration
D) Increased ATP production
Explanation: The C4 pathway concentrates CO₂ in bundle sheath cells, where RuBisCO can more efficiently fix carbon without being affected by oxygen. This adaptation minimizes photorespiration, which wastes energy and reduces carbon fixation efficiency.
14. Which molecule acts as the final electron acceptor in the light-dependent reactions of photosynthesis?
A) Oxygen
B) Carbon dioxide
C) NADP+
D) ATP
Explanation: In the light-dependent reactions, NADP+ accepts electrons from the electron transport chain in Photosystem I, forming NADPH. This molecule is then used in the Calvin cycle to help convert carbon dioxide into glucose.
15. What is the term for ATP synthesis linked to the electron transport chain in the thylakoid membrane?
A) Oxidative phosphorylation
B) Photophosphorylation
C) Substrate-level phosphorylation
D) Cyclic phosphorylation
Explanation: Photophosphorylation is the synthesis of ATP in the chloroplasts during the light-dependent reactions. This process uses light energy to drive electrons through the electron transport chain, creating a proton gradient that powers ATP synthase.
16. In which specific structure within the chloroplast do light-dependent reactions occur?
A) Stroma
B) Grana
C) Thylakoid membrane
D) Outer membrane
Explanation: Light-dependent reactions take place in the thylakoid membrane, where chlorophyll and other pigments capture light energy, generating ATP and NADPH.
17. The splitting of water in photosynthesis releases which of the following products?
A) Glucose and NADPH
B) Oxygen, protons, and electrons
C) Carbon dioxide and water
D) ATP and glucose
Explanation: Water molecules are split in Photosystem II, releasing oxygen (O₂) as a byproduct, along with protons and electrons that participate in the electron transport chain.
18. Which of the following wavelengths of light is least effective for photosynthesis?
A) Blue
B) Green
C) Red
D) Violet
Explanation: Green light is least effective for photosynthesis because chlorophyll reflects green light rather than absorbing it, which is why plants appear green.
19. Who is credited with mapping the complete pathway of carbon assimilation in photosynthesis?
A) Melvin Calvin
B) Joseph Priestley
C) Jan Ingenhousz
D) Julius von Sachs
Explanation: Melvin Calvin, through his experiments with radioactive carbon-14, elucidated the Calvin cycle, the pathway of carbon fixation in photosynthesis.
20. What is the primary purpose of accessory pigments like carotenoids in photosynthesis?
A) Generate ATP
B) Capture a broader spectrum of light
C) Convert glucose to starch
D) Release oxygen
Explanation: Accessory pigments like carotenoids absorb additional wavelengths of light and transfer this energy to chlorophyll a, increasing the efficiency of photosynthesis.
21. The first stable product of carbon fixation in the C3 pathway is...
A) 3-phosphoglycerate
B) Oxaloacetate
C) Malate
D) Pyruvate
22. Which molecule acts as the primary acceptor of carbon dioxide in C4 plants?
A) RuBP
B) PEP
C) PGA
D) NADPH
23. What adaptation helps C4 plants reduce photorespiration?
A) More chlorophyll
B) Bundle sheath cells with higher CO₂ concentration
C) Higher production of ATP
D) Increased oxygen absorption
24. In which cells does the Calvin cycle occur in C4 plants?
A) Mesophyll cells
B) Stomatal cells
C) Bundle sheath cells
D) Epidermal cells
25. Which molecule is regenerated during the Calvin cycle, allowing it to continue?
A) Glucose
B) RuBP
C) ATP
D) NADPH
26. During the Calvin cycle, carbon dioxide is fixed into which molecule?
A) ATP
B) NADPH
C) Ribulose-1,5-bisphosphate
D) Glucose
27. The Z-scheme of photosynthesis refers to...
A) The Calvin cycle
B) Cyclic photophosphorylation
C) Non-cyclic electron transport
D) Glycolysis
28. In the light-dependent reactions, ATP is synthesized by the movement of protons through...
A) NADP reductase
B) Cytochrome complex
C) ATP synthase
D) RuBisCO
29. The main function of NADPH in the Calvin cycle is to...
A) Fix carbon dioxide
B) Provide electrons for reducing carbon compounds
C) Produce ATP
D) Release oxygen
30. Which enzyme is responsible for fixing carbon dioxide in C4 plants?
A) RuBisCO
B) PEP carboxylase
C) ATP synthase
D) NADP reductase