botany

Chlorophyll breaks down in autumn leaves, unmasking yellow and orange carotenoid pigments that were present all along. Meanwhile, trees synthesize new red and purple anthocyanins, while shorter days and cooler nights trigger senescence—a programmed shutdown that eventually leads the tree to seal off and drop each leaf at a specialized abscission layer. This cascade of biochemical events helps trees conserve resources for winter.

An intact onion does nothing to your eyes. But cutting one releases enzymes that act on sulfur compounds, triggering a chemical cascade that produces syn-propanethial-S-oxide — a volatile gas that irritates your cornea and forces your eyes to water. The science behind this everyday kitchen reaction reveals how plants weaponize chemistry as a defense mechanism.