C4 photosynthesis

C4 photosynthesis is an alternative biochemical pathway for capturing light energy that evolved in plants facing hot, dry climates. Unlike the more ancient C3 photosynthesis, which fixes Carbon dioxide directly into a three-carbon compound, C4 plants first concentrate CO₂ into a four-carbon molecule—hence the name. This spatial separation of the initial fixation step from the Calvin cycle dramatically reduces photorespiration, a wasteful process that plagues C3 plants in arid conditions.

The efficiency comes from a two-cell system: mesophyll cells perform the initial capture, then shuttle the concentrated carbon to bundle sheath cells where the Calvin cycle operates. This "Chloroplast division of labor" allows C4 plants to thrive in contemporary hot grasslands, deserts, and tropical savannas.

Economically significant C4 plants include maize, sugarcane, and sorghum—crops that dominate global agriculture. They represent one of evolution's most elegant solutions to environmental stress, achieving up to twice the photosynthetic efficiency of C3 relatives under the same harsh conditions.

The mechanism was fully elucidated through mid-20th century research into plant biochemistry, revealing how evolutionary pressure sculpted metabolism itself.

Related

Photosynthesis, C3 photosynthesis, NADPH, Water, Environmental impact