The leaves of the world comprise countless billion elaborations of a single, simple machine designed for one job only – a job upon which hinges humankind. Leaves make sugar. Plants are the only things in the universe that can make sugar out of nonliving inorganic matter. All the sugar that you have ever eaten was first made within a leaf. Without a constant supply of glucose to your brain, you will die. Period. Under duress, your liver can make glucose out of protein or fat – but that protein or fat was originally constructed from a plant sugar within some other animal. It’s inescapable: at this very moment, within the synapses of your brain, leaves are fueling thoughts of leaves.
Hope Jahren, Lab Girl
botany, science