a leaf lesson

October 15, 2021
Autumn leaves arranged against a white background.

Photo: Mae Axelrod

Think back to grade school when you learned about photosynthesis—the process by which plants use sunlight to manufacture glucose for their “food.” In autumn, as days become shorter, there is not enough sunlight for photosynthesis so trees begin to shut down this process. Green chlorophyll, a chemical essential to the photosynthetic process, slowly disappears from the leaves.

As the bright green fades away, oranges and yellows emerge. Small amounts of these colors have been in the leaves all along but were hidden by the green chlorophyll. In some species, like maples, glucose is trapped in the leaves after photosynthesis stops. Sunlight and the cool nights of autumn cause the leaves turn this glucose into red and purple tones.

All adding up to an awesome autumn display.