Photosynthesis

Photosynthesis – 50 MCQs with Explanations (BPSC Prelims)

PYQs (Q1–10)

1. The gas released during photosynthesis is:
   a) Carbon dioxide
   b) Oxygen
   c) Nitrogen
   d) Hydrogen
   Answer: b
   Explanation: Oxygen is released as a by-product during photolysis of water. (BPSC 64th)

2. The green pigment responsible for photosynthesis is:
   a) Haemoglobin
   b) Chlorophyll
   c) Melanin
   d) Anthocyanin
   Answer: b
   Explanation: Chlorophyll absorbs sunlight for the light reaction. (BPSC 65th)

3. Photosynthesis mainly occurs in which plant part?
   a) Root
   b) Leaf
   c) Stem
   d) Flower
   Answer: b
   Explanation: Leaves contain chloroplasts that carry out photosynthesis. (BPSC Teacher 2023)

4. Which is the first stable product of photosynthesis in C3 plants?
   a) Pyruvic acid
   b) Phosphoglyceric acid (PGA)
   c) Malic acid
   d) Glucose
   Answer: b
   Explanation: PGA is the first stable compound in the Calvin cycle. (BPSC CDPO)

5. The primary source of energy for photosynthesis is:
   a) Earth
   b) Fire
   c) Sunlight
   d) Moonlight
   Answer: c
   Explanation: Sunlight provides energy for the photochemical reactions. (BPSC 66th)

6. Site of light reaction in chloroplast:
   a) Stroma
   b) Cytoplasm
   c) Grana
   d) Nucleus
   Answer: c
   Explanation: Grana (thylakoid membranes) are the site of light-dependent reactions. (BPSC 67th)

7. Which one is required for photosynthesis?
   a) Water only
   b) CO₂ only
   c) Sunlight only
   d) Water, CO₂ and Sunlight
   Answer: d
   Explanation: All three are essential inputs for the process. (BPSC 62nd)

8. Which process is opposite to photosynthesis?
   a) Digestion
   b) Transpiration
   c) Respiration
   d) Germination
   Answer: c
   Explanation: Photosynthesis stores energy; respiration releases it.

9. In which cell organelle does photosynthesis occur?
   a) Mitochondria
   b) Chloroplast
   c) Ribosome
   d) Vacuole
   Answer: b
   Explanation: Chloroplast contains pigments and enzymes for photosynthesis.

10. Photosynthesis takes place in the presence of:
    a) Green light
    b) Blue and red light
    c) Yellow light
    d) All of these
    Answer: b
    Explanation: Blue and red wavelengths are most effective for photosynthesis.

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NCERT-Based (Q11–30)

1. The first step of photosynthesis is:
   a) CO₂ fixation
   b) Splitting of water
   c) Glucose formation
   d) ATP synthesis
   Answer: b
   Explanation: Light energy splits water molecules (photolysis).

2. The end product of photosynthesis is:
   a) ATP
   b) Oxygen
   c) Glucose
   d) CO₂
   Answer: c
   Explanation: Glucose is stored as a product of photosynthesis.

3. The stomata help in:
   a) Absorption of water
   b) Transport of food
   c) Exchange of gases
   d) Protein synthesis
   Answer: c
   Explanation: Stomata regulate CO₂ intake and O₂ release.

4. Photosynthesis is a/an:
   a) Exothermic reaction
   b) Endothermic reaction
   c) Neutral reaction
   d) Combustion reaction
   Answer: b
   Explanation: It requires energy input (sunlight), hence endothermic.

5. Which of the following is not required for photosynthesis?
   a) Chlorophyll
   b) Light
   c) Oxygen
   d) CO₂
   Answer: c
   Explanation: Oxygen is a product, not a requirement.

6. Which pigment absorbs most blue light?
   a) Chlorophyll-a
   b) Chlorophyll-b
   c) Carotenoid
   d) Xanthophyll
   Answer: b
   Explanation: Chlorophyll-b absorbs more blue-violet light.

7. Stroma of the chloroplast is the site of:
   a) Light reaction
   b) Calvin cycle
   c) Respiration
   d) Krebs cycle
   Answer: b
   Explanation: Calvin cycle (dark reaction) occurs in stroma.

8. The process of carbon fixation is known as:
   a) Hill reaction
   b) Calvin cycle
   c) Glycolysis
   d) Krebs cycle
   Answer: b
   Explanation: CO₂ is fixed into sugars in the Calvin cycle.

9. Which mineral activates the enzymes of photosynthesis?
   a) Magnesium
   b) Iron
   c) Zinc
   d) Sodium
   Answer: a
   Explanation: Mg is a central atom in chlorophyll.

10. The process of photolysis releases:
    a) Nitrogen
    b) Oxygen
    c) Carbon
    d) Phosphorus
    Answer: b
    Explanation: Splitting of water releases oxygen as a byproduct.

11. The photochemical phase of photosynthesis is also called:
    a) Dark reaction
    b) Light reaction
    c) Anaerobic phase
    d) Krebs cycle
    Answer: b
    Explanation: Occurs in light, involves ATP and NADPH generation.

12. Calvin cycle was discovered by:
    a) Robert Hooke
    b) Melvin Calvin
    c) Watson
    d) Lamarck
    Answer: b
    Explanation: He used radioactive CO₂ to trace the carbon pathway.

13. Photosynthesis occurs in:
    a) All living cells
    b) Cells with mitochondria
    c) Cells with chloroplast
    d) Animal cells
    Answer: c
    Explanation: Only chloroplast-containing cells perform photosynthesis.

14. Green plants are also called:
    a) Consumers
    b) Heterotrophs
    c) Decomposers
    d) Autotrophs
    Answer: d
    Explanation: They produce food using sunlight and CO₂.

15. Which of these reduces during photosynthesis?
    a) CO₂
    b) O₂
    c) H₂O
    d) Glucose
    Answer: a
    Explanation: CO₂ is consumed to form glucose.

16. The gas taken in by plants is:
    a) O₂
    b) CO₂
    c) N₂
    d) H₂
    Answer: b
    Explanation: CO₂ is absorbed from the atmosphere.

17. In which part of the chloroplast does the light reaction occur?
    a) Stroma
    b) Thylakoid
    c) Matrix
    d) Outer membrane
    Answer: b
    Explanation: Thylakoids contain chlorophyll for light reaction.

18. Which of the following is a light-dependent process?
    a) Formation of sugar
    b) Formation of NADPH
    c) Fixation of CO₂
    d) Calvin cycle
    Answer: b
    Explanation: Light energy is used to make NADPH and ATP.

19. Which of the following does not affect photosynthesis?
    a) Temperature
    b) Light intensity
    c) CO₂ concentration
    d) Moonlight
    Answer: d
    Explanation: Moonlight intensity is too low for photosynthesis.

20. The maximum photosynthesis takes place in which spectrum?
    a) Green
    b) Yellow
    c) Blue and red
    d) Black
    Answer: c
    Explanation: Blue and red wavelengths are absorbed best.

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Predicted and Reference-Based Questions (Q31–50)

1. Which component provides electrons in photosynthesis?
   a) CO₂
   b) O₂
   c) H₂O
   d) Sunlight
   Answer: c
   Explanation: Water splits to donate electrons for photosynthesis.

2. How many ATP molecules are used in one turn of the Calvin cycle?
   a) 1
   b) 2
   c) 3
   d) 18
   Answer: c
   Explanation: Three ATP are consumed per cycle turn.

3. How many molecules of CO₂ are fixed to form one glucose?
   a) 3
   b) 4
   c) 6
   d) 12
   Answer: c
   Explanation: Six CO₂ molecules are needed to form C₆H₁₂O₆.

4. Which of the following is not a product of light reaction?
   a) ATP
   b) NADPH
   c) O₂
   d) Glucose
   Answer: d
   Explanation: Glucose forms in the Calvin cycle (dark reaction).

5. Who proved oxygen is released during photosynthesis?
   a) Calvin
   b) Hill
   c) Jan Ingenhousz
   d) Priestley
   Answer: d
   Explanation: Joseph Priestley discovered O₂ evolution.

6. Plants appear green because they:
   a) Reflect green light
   b) Absorb green light
   c) Emit green light
   d) None
   Answer: a
   Explanation: Chlorophyll reflects green wavelengths.

7. In CAM plants, CO₂ fixation occurs at:
   a) Daytime
   b) Night
   c) Noon
   d) Anytime
   Answer: b
   Explanation: CAM plants open stomata at night to conserve water.

8. Which of the following plants use C4 pathway?
   a) Wheat
   b) Rice
   c) Maize
   d) Pea
   Answer: c
   Explanation: Maize is a C4 plant with high photosynthetic efficiency.

9. Chloroplast was discovered by:
   a) Schleiden
   b) Mayer
   c) Altmann
   d) Sachs
   Answer: c
   Explanation: Altmann observed chloroplasts in 1886.

10. Which organelle is semiautonomous and has its own DNA?
    a) Mitochondria
    b) Ribosome
    c) Chloroplast
    d) Nucleus
    Answer: c
    Explanation: Chloroplasts have circular DNA like prokaryotes.

11. How many types of photosystems are there in light reaction?
    a) One
    b) Two
    c) Three
    d) Four
    Answer: b
    Explanation: Photosystem I and II absorb different light wavelengths.

12. What is photophosphorylation?
    a) ATP production using CO₂
    b) ATP production using light
    c) Glucose breakdown
    d) Water transport
    Answer: b
    Explanation: Light energy drives ATP synthesis.

13. Which scientist discovered the Hill reaction?
    a) Hill
    b) Priestley
    c) Blackman
    d) Ruben
    Answer: a
    Explanation: Hill demonstrated O₂ release from water.

14. How many molecules of NADPH are required for one glucose?
    a) 3
    b) 6
    c) 12
    d) 2
    Answer: b
    Explanation: Six NADPH are needed to reduce six CO₂ molecules.

15. Calvin cycle is also called:
    a) Light reaction
    b) Photolysis
    c) Dark reaction
    d) Electron transport
    Answer: c
    Explanation: Calvin cycle does not require light directly.

16. Rubisco is an enzyme involved in:
    a) CO₂ fixation
    b) Water splitting
    c) ATP synthesis
    d) NADPH production
    Answer: a
    Explanation: Rubisco fixes CO₂ to RuBP in Calvin cycle.

17. Photorespiration occurs in:
    a) C3 plants
    b) C4 plants
    c) CAM plants
    d) All
    Answer: a
    Explanation: C3 plants show photorespiration due to O₂ binding to Rubisco.

18. What is the main limiting factor of photosynthesis?
    a) Temperature
    b) CO₂ concentration
    c) Light intensity
    d) Water
    Answer: b
    Explanation: CO₂ availability directly affects rate of photosynthesis.

19. Van Niel proposed that:
    a) CO₂ is fixed
    b) Water is split in photosynthesis
    c) O₂ is released from CO₂
    d) Glucose is made in stroma
    Answer: b
    Explanation: He suggested O₂ comes from H₂O, not CO₂.

20. The process of using sunlight to synthesize glucose is called:
    a) Glycolysis
    b) Photosynthesis
    c) Respiration
    d) Fermentation
    Answer: b
    Explanation: Photosynthesis converts light into chemical energy.