Photosynthesis

'Photosynthesis' literally means 'synthesis using sunlight'. About 10 % of the solar radiation striking on earth is absorbed by the green plants and only 3-6 % is utilized in the photosynthesis. Photosynthesis is only biological process on earth that can harvest solar energy into chemical energy, more specifically, into carbohydrates. Photosynthesis in green plants is thought to be evolved 1 billion years ago by endosymbiosis with ancient cyanobacterium. Nearly 3 × 10²¹ Joules of solar energy is harvested by the photosynthetic organisms for fixation of 2 × 10¹¹ tons CO₂ per year.

Photosynthesis is fixation of incorganic carbon to organic carbon

During the process of photosynthesis light energy is captured in the form of NADPH and ATP, which drives the reduction of atmospheric carbon dioxide (CO₂) into carbohydrates (C₆H₁₂O₆). Water (H₂O) is broken down and oxygen (O₂) is released into the atmosphere.

6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂

These carbohydrates are used for the generation of cellular energy and supports all the life forms on earth.
The process of photosynthesis is very robust, complex, coordinated and controlled process that can be understood under following heads.

• Discovery
• Site of photosynthesis
• Distribution of pigments
• Structure of pigments (Chlorophylls, carotenoids and phycobilins)
• Light absorption
• Photosystems (Quantasomes and light harvesting complex)
• Light reaction (Z-scheme and photophosphorylation)
• Dark reaction (C3 cycle or Calvin cycle or Calvin-Benson cycle)
  • C2 Cycle (Photorespiration)
  • C4 Cycle (Hatch and Slack cycle)
  • CAM Cycle (Crassulacean Acid Metabolism)

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First published on 13-04-2021
Last updated on 14-04-2021