The tree outside your window didn't grow by eating soil. Almost all of its wood was built out of thin air.
The recipe: carbon dioxide from the air, water from the soil, and sunlight. Roots soak up the water, but nothing pumps it up the tree. Leaves lose water through tiny pores, and that evaporation pulls a continuous column of water all the way up the trunk. That pull is one reason the tallest trees top out around 120 metres (the tallest living tree is about 116 m).
Zoom into a leaf and its surface is dotted with those pores, called stomata. Two guard cells swell and bow apart to open each one and let carbon dioxide in. Inside the cells, chloroplasts are packed with chlorophyll, which absorbs red and blue light and bounces green back. That's why leaves look green.
The twist: the oxygen you breathe comes from water. Light splits water apart inside the chloroplast. Then the enzyme Rubisco turns the carbon dioxide into sugar, and chains of that sugar (cellulose) become wood.
Sources:
- OpenStax Biology 2e, 30.5 Transport of Water and Solutes in Plants: https://openstax.org/books/biology-2e/pages/30-5-transport-of-water-and-solutes-in-plants
- Koch et al., "The limits to tree height", Nature 428, 851 (2004): https://doi.org/10.1038/nature02417
- Ruben et al., "Heavy Oxygen (O18) as a Tracer in the Study of Photosynthesis", JACS 63, 877 (1941): https://doi.org/10.1021/ja01848a512
- Bar-On & Milo, "The global mass and average rate of rubisco", PNAS 116, 4738 (2019): https://doi.org/10.1073/pnas.1816654116
- Taiz & Zeiger, Plant Physiology and Development (chlorophyll absorption, stomata)
Where does the oxygen you breathe come from? Tell me in the comments before the video answers it.
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I'm Haris, a systems engineer. I make short videos about how the world around you actually works.
More of my work: https://bytefy.in
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