Video narration
How do some plants keep photosynthesis working in hot conditions? Think of C4 as a carbon relay, not four separate steps. A mesophyll cell captures carbon dioxide and packs it into a four-carbon molecule. That molecule carries carbon to a bundle-sheath cell, where it releases carbon dioxide beside Rubisco, the enzyme that starts sugar-building reactions. The trick isn't a different sugar-making cycle. It's handing carbon to a second cell, concentrating carbon dioxide beside Rubisco. Then pyruvate returns to the mesophyll cell. The plant spends extra energy to rebuild the carbon-capturing molecule, ready for another relay. With more carbon dioxide near Rubisco, it grabs less oxygen, reducing photorespiration-the wasteful process that slows sugar production. So how do these plants keep photosynthesis working in heat? They run a carbon relay: capture carbon in mesophyll cells, release concentrated carbon dioxide beside Rubisco in bundle-sheath cells, and reduce photorespiration, at an extra energy cost.