How does photosynthesis provide starting materials for organic compounds?

Photosynthesis provides the essential starting materials for organic compounds by converting inorganic carbon into stable, energy-rich molecules through a process known as carbon fixation.

During the light-dependent reactions, light energy drives the oxidation of water, which releases electrons, hydrogen ions, and oxygen. These electrons and hydrogen ions are used to generate ATP and NADPH, which provide the necessary energy and reducing power for the subsequent "dark" reactions.12

In the Calvin-Benson cycle, these components reduce carbon dioxide into glyceraldehyde-3-phosphate (Gal3P), a three-carbon sugar phosphate. Gal3P serves as the primary building block for:2

• Carbohydrates: Such as sucrose for transport and starch for energy storage.134
• Amino Acids: Formed when carbon skeletons from Gal3P are combined with amino and sulfhydryl groups derived from the reduction of nitrate and sulfate.14
• Lipids and Pigments: Synthesized through further metabolic pathways originating from these carbon intermediates.4

Ultimately, this assimilation of inorganic carbon into organic form sustains nearly all food webs on Earth.5