Photosynthesis
Year of Discovery: 1779
What Is It? Plants use sunlight to convert carbon dioxide in the air into new
plant matter.
Who Discovered It? Jan Ingenhousz
Why Is This One of the 100 Greatest?
Photosynthesis is the process that drives plant production all across Earth. It is also the
process that produces most of the oxygen that exists in our atmosphere for us to breathe.
Plants and the process of photosynthesis are key elements in the critical (for humans and
other mammals) planetary oxygen cycle.
When Jan Ingenhousz discovered the process of photosynthesis, he vastly improved
our basic understanding of how plants function on this planet and helped science gain a
better understanding of two important atmospheric gasses: oxygen and carbon dioxide.
Modern plant engineering and crop sciences owe their foundation to Jan Ingenhousz’s
discovery.
How Was It Discovered?
Jan Ingenhousz was born in Breda in the Netherlands in 1730. He was educated as a
physician and settled down to start his medical practice back home in Breda.
In 1774 Joseph Priestley discovered oxygen and experimented with this new, invisible
gas. In one of these tests, Priestley inserted a lit candle into a jar of pure oxygen and let it
burn until all oxygen had been consumed and the flame went out. Without allowing any
new air to enter the jar, Priestley placed mint sprigs floating in a glass of water in the jar to
see if the mint would die in this “bad” air. But the mint thrived. After two months, Priestley
placed a mouse in the jar. It also lived—proving that the mint plant had restored oxygen to
the jar’s air. But this experiment didn’t always work. Priestley admitted that it was a mystery and then moved on to other studies.
In 1777, Ingenhousz read about Priestley’s experiments and was fascinated. He could
focus on nothing else and decided to investigate and explain Priestley’s mystery.
Over the next two years, Ingenhousz conducted 500 experiments trying to account for
every variable and every possible contingency. He devised two ways to trap the gas that a
plant produced. One was to enclose the plant in a sealed chamber. The other was to submerge the plant.
45