This reminds me of my favorite "thought experiment" to poke at intuition: with no other information that what most people learn in elementary/middle school science (or what I would assume is taught, i.e. the water and respiration cycles), where does the majority of a tree's mass come from?
First we might look at dirt, but that doesn't quite pan out; where does the mass come from, and how would it be replenished? We don't see gaps slowly start forming around roots, and dirt doesn't just build up in other places, so that's probably not it.
Next we might look at water, but water is only made of hydrogen and oxygen, and the oxygen is released. The water also brings in nutrients, but there's no way it brings in enough to generate the majority of a trees mass.
So there's only one place left, which is never anyone's first guess and almost never crosses anyone's mind at first glance: air. It's around this point that most people realize that a majority of a tree is carbon, which all comes in from the air as carbon dioxide.
The correct answer is water though, not air. Air only accounts for the Carbon content of the tree, which is a big part, but still a minority.
First, a live tree contains a lot of water (30-50%), that's why you need to let wood dry a lot before burning it.
And there's something else:
> Next we might look at water, but water is only made of hydrogen and oxygen, and the oxygen is released.
Not all oxygen is released. All oxygen contained in a plants molecule (mostly cellulose and hemicellulose, which are polymers of glucose, and lignin) comes from water. And there's a lot of it: there's as much Oxygen as Carbon in a glucose molecule.
Plant carbohydrates are made directly from CO2 in the Calvin Cycle.
The Calvin Cycle is the source of all of the carbohydrate building blocks in the plant, and I’m pretty sure that oxygen from H2O does not enter the equation, just CO2 and some enzymes and cofactors.
If so, the vast majority of the mass is from the air.
(H might originate from water but its mass is pretty trivial compared to C and O)
First we might look at dirt, but that doesn't quite pan out; where does the mass come from, and how would it be replenished? We don't see gaps slowly start forming around roots, and dirt doesn't just build up in other places, so that's probably not it.
Next we might look at water, but water is only made of hydrogen and oxygen, and the oxygen is released. The water also brings in nutrients, but there's no way it brings in enough to generate the majority of a trees mass.
So there's only one place left, which is never anyone's first guess and almost never crosses anyone's mind at first glance: air. It's around this point that most people realize that a majority of a tree is carbon, which all comes in from the air as carbon dioxide.