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Light is the energy source for the light-dependent reactions in the thylakoid membranes. Light energy excites electrons in chlorophyll, drives the photolysis of water and is used to make ATP and reduced NADP. These products are then used in the Calvin cycle to reduce GP to GALP.
Two features of light matter. Light intensity sets how fast ATP and reduced NADP are made. At low light intensity, the rate of photosynthesis rises roughly in proportion to light intensity, then levels off when another factor becomes limiting. Wavelength matters because chlorophylls absorb mainly red and blue light; green light is mostly reflected, so it drives little photosynthesis.
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Key terms in this lesson
- nadp
- A coenzyme that acts as a hydrogen acceptor in the light-dependent reactions of photosynthesis, becoming reduced NADP when it accepts hydrogen.
- gp
- The three-carbon compound formed when RuBP combines with carbon dioxide in the Calvin cycle, before being reduced to GALP.
- rubp
- Ribulose bisphosphate, the five-carbon compound that combines with carbon dioxide in the Calvin cycle, catalysed by RUBISCO.
More in Photosynthesis
- The Calvin Cycle
- The Products of Photosynthesis
- C4 Plants
- Rubisco
- Limiting Factors of Photosynthesis
- Carbon Dioxide
- Temperature
- Limiting Factors in the Wild
All 20 lessons in Photosynthesis · All Edexcel A-level Biology topics