bio

Stomata

The microscopic pores on a leaf's surface, each a slit between two specialised cells that swell and slacken to widen or close it. They exist because a leaf must let CO₂ in to eat, and gas can only enter through a hole. But a leaf's interior is wet, so any hole that admits gas also lets water vapour out — no membrane, no valve, no trick of geometry separates the two directions. Each stoma is therefore where the central bargain of a leaf's life is struck, and the only thing the plant controls is how far to open it, right now.