How C4 plants concentrate carbon dioxide inside leaves

Some plants build a CO₂-rich space inside their leaves

C4 plants use two steps to gather carbon dioxide around the enzyme that performs a key part of photosynthesis. This extra CO₂ helps them waste less energy on a side process called photorespiration. It makes C4 plants especially effective in hot, bright places.

A trench held off a much larger force

At the Battle of the Trench in Medina in 627, about 3,000 Muslim defenders used a trench across approaches open to cavalry. They held off a coalition of about 10,000 for two weeks, until it withdrew.

The Gateway Arch's tram cars tilt to stay level inside its curved legs

Visitors traveling to the top of St. Louis's Gateway Arch ride in small enclosed tram compartments. Because the track curves as it climbs, the cars use a leveling mechanism to keep passengers upright. The unusual system combines features of an elevator and a Ferris wheel to follow a structure that is neither straight nor vertical.

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How C4 plants concentrate carbon dioxide inside leaves

Some plants build a CO₂-rich space inside their leaves

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