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vasopressin334 t1_j9z0vri wrote

To be precise, plants convert water and carbon dioxide into carbohydrates through the process of photosynthesis. Those carbohydrates are not just used for energy - they are made into structural molecules that make up the plants themselves. For instance, cell walls in plants are essentially sugar polymers.

The lost water is therefore "captured" by the structure of the plant in an equal ratio to the carbon dioxide captured. This process is commonly referred to as "carbon capture" because people care more about atmospheric carbon dioxide.

Edit: This got some attention so let me add two more specific examples of water capture. The cellulose that makes up virtually every tree is a sugar polymer, so trees themselves are literally made of sugar. All of that involves captured water molecules that will only ever be released when the tree decays, burns down, or is eaten by termites.

A very different example is the fat in a camel's hump. When fatty acids are made, a great deal of water molecules are stripped of their hydrogens and the oxygen is released. Those water molecules are gone in a real sense, as the oxygen in them is gone. However, digesting that fatty acid requires adding the oxygen atoms back, and water and carbon dioxide is released. This is how camels "store" water in a form that is highly compact and actually devoid of the oxygen atom needed to make the water.

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katlian t1_ja0w0el wrote

That water isn't permanently lost though. When the structure of the plant oxidizes either slowly (decomposition or animal digestion) or rapidly (fire) most of the hydrogen combines with oxygen from the atmosphere to form new water molecules.

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vasopressin334 t1_ja10crm wrote

While it is clearly true that the water is not “lost” and much of the water sequestered in this way is released through various degradation processes, some water is captured, much the way that some carbon is captured. This captured water makes up not only the organic molecules present in all fertile soil but also the bulk of all biomass.

However, since the entire biomass of every living thing on earth is about 10 million times less than the mass of all water on earth, the water captured in this way will never be more than a negligible amount.

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Smallpaul t1_ja6wry7 wrote

When wood is burned, water is a byproduct?

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BobbyP27 t1_ja70ykd wrote

Chemically speaking, wood contains mostly carbon, hydrogen and oxygen atoms. When it is burned, the hydrogen atoms end up as water vapour.

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