Photosynthesis is the natural process by which light energy is transformed into chemical energy, forming the foundation of life on Earth. In this process, photons are absorbed by specialized organelles—chloroplasts in plant cells—and converted into high‑energy electrons that ultimately drive the synthesis of sugars. The two main stages are the light‑dependent reactions and the Calvin‑cycle (dark reactions).
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Pigments are chromophoric molecules that absorb specific wavelengths of light while reflecting others. This selective absorption not only creates the colorful palette of flowers and foliage but also plays a critical role in harvesting sunlight efficiently. Seasonal pigment shifts, for example, turn leaves golden or crimson in autumn.
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Chlorophyll—predominantly chlorophyll‑a and chlorophyll‑b—captures photons across the blue‑green and red regions of the spectrum, transferring their energy to the photosynthetic machinery. These high‑energy electrons are then used during the Calvin‑cycle to reduce carbon dioxide into glucose.
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Carotenoids (carotenes, xanthophylls) absorb in the blue‑green and provide yellow, orange, and red hues. They also protect chlorophyll from photo‑oxidative damage. Phycobilins, found in cyanobacteria and red algae, include phycocyanin (blue) and phycoerythrin (red), enabling these organisms to capture light in deep or turbid waters.
By orchestrating light absorption and energy transfer, pigments underpin photosynthesis, sustaining ecosystems and the planet’s oxygen supply.
