A doctor proved plants breathe backward from animals, and only in daylight
In 1771, Joseph Priestley found that a sprig of mint left in a sealed jar could restore air a candle had used up, but couldn't explain why. In 1779, physician Jan Ingenhousz showed the missing piece: the effect only worked in sunlight and only in the plant's green parts, revealing that plants absorb carbon dioxide and release oxygen when lit — roughly the reverse of animal respiration. His work founded the study of photosynthesis, though the word itself wasn't coined until decades later.