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Difficulty: MediumPlant Nutrition and Photosynthesis

During photosynthesis, light energy absorbed by chlorophyll drives essential chemical conversions within the thylakoid membranes of chloroplasts. Which of the following biological processes occurs specifically during this light-dependent stage?

  1. Photolysis of water yielding oxygen gas, protons, and high-energy energy carriersAnswer
  2. B
    Fixation of carbon dioxide by ribulose bisphosphate to form glycerate 3-phosphate
  3. C
    Reduction of triose phosphate to synthesize glucose and regenerate RuBP
  4. D
    Translocation of synthesized organic sugars from leaves to storage roots

Answer

Photolysis of water yielding oxygen gas, protons, and high-energy energy carriers occurs specifically during the light-dependent stage.
The light-dependent stage of photosynthesis occurs in the thylakoid membranes of chloroplasts. Light energy absorbed by chlorophyll causes the photolysis of water (2H2O→4H++4e−+O22H_2O \rightarrow 4H^+ + 4e^- + O_2), releasing oxygen gas as a byproduct and generating ATP and reduced NADP (NADPH) required for the dark reaction.

Step-by-Step Solution

1
Identify the biological site and primary events of the light-dependent stage of photosynthesis.
The light-dependent reactions occur within the thylakoid membranes of chloroplasts, initiated by light absorption by chlorophyll.
Photon absorption excites electrons to drive water splitting and energy carrier generation.
2
Distinguish between light-dependent reaction products and light-independent Calvin cycle steps.
Photolysis of water (2H2O→4H++4e−+O22H_2O \rightarrow 4H^+ + 4e^- + O_2) produces oxygen gas, ATPATP, and NADPHNADPH in thylakoids, whereas carbon fixation, reduction, and sugar synthesis occur in the stroma.
Light energy is directly required to split water molecules, whereas carbon fixation relies on chemical products in the stroma.

Key Concept

Light-dependent stage of photosynthesis and photolysis of water
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Topics

Plant Nutrition and Photosynthesis

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