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Light Reaction

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Estimated time: 4 minutes
  • Definition: Photolysis
  • Definition: Photophosphorylation
CISCE: Class 10

Definition: Photolysis

Photolysis occurs in the grana of a chloroplast and is defined as the splitting of H2O molecules into hydrogen ions and oxygen in the presence of light.

CISCE: Class 10

Definition: Photophosphorylation

Photophosphorylation is the process of converting ADP into energy-rich ATP by adding an inorganic phosphate (Pi), using energy from light (photons).

CBSE: Class 12

Key Points: Light Reaction

  • Light Harvesting Complexes (LHC) - Made up of hundreds of pigment molecules bound to proteins. Found in PS I and PS II. Help absorb different wavelengths of light for efficient photosynthesis.
  • Antennae System - In each photosystem, all pigments except one chlorophyll a molecule form the antennae (light-harvesting system). They absorb light and pass energy to the reaction centre.
  • Reaction Centre - The single chlorophyll a molecule that directly participates in the photochemical reaction. It is different in PS I and PS II.
  • PS I - Reaction centre = P700 (absorbs light at 700 nm).
  • PS II - Reaction centre = P680 (absorbs light at 680 nm).
  • Steps of Light Reaction - Light absorption → Water splitting → Oxygen release → ATP and NADPH production.

Shaalaa.com | Photosynthesis Part 2

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