31. Which one of the following statements related to photosynthesis is NOT correct?
(1) Light reaction takes place in the thylakoid membranes
(2) ATP and NADPH are produced in thylakoid membranes.
(3) Lumen is the enclosed interconnected region of the thylakoid membranes.
(4) NAPDH is produced during carbon reactions by the enzymes present in stroma.

The statement that is NOT correct is (4): NADPH is produced during carbon reactions by the enzymes present in stroma. In actuality, NADPH is produced during the light reactions within the thylakoid membrane; it is then used in the Calvin cycle (carbon reactions) but not produced by stromal enzymes.​

Photosynthesis: Correct and Incorrect Statements

Introduction

Key phrase: NADPH ATP light reactions thylakoid stroma photosynthesis

Photosynthesis involves a series of elegantly organized processes within chloroplasts—light reactions generate ATP and NADPH in the thylakoid membranes, while the Calvin cycle (carbon reactions) occurs in the stroma, using these products for carbon fixation.​

Explanation of Each Option

• (1) Light reaction takes place in the thylakoid membranes

  • Correct. The light-dependent reactions are localized within thylakoid membranes, where the photosystems and electron transport complexes reside.​

• (2) ATP and NADPH are produced in thylakoid membranes

  • Correct. Both ATP and NADPH are generated in the thylakoid membrane during the light reactions using solar energy, electron transport, and chemiosmosis.​

• (3) Lumen is the enclosed interconnected region of the thylakoid membranes

  • Correct. The lumen is the internal aqueous space within thylakoids, important for establishing the proton gradient during light reactions.​

• (4) NADPH is produced during carbon reactions by the enzymes present in stroma

  • NOT correct. NADPH is produced in the light reactions at the thylakoid membrane; during carbon reactions in the stroma, NADPH is consumed for CO₂ fixation but not generated.​

Key Facts: Site of NADPH and ATP Production

• ATP and NADPH are generated by light reactions in the thylakoid membrane.

• NADPH is a reducing agent consumed, not produced, in the Calvin cycle in the stroma.​