Saturday, December 1, 2012

Where does the Mass of a Tree come from?

This was a recent interesting topic of conversation.  In addition, the answer led to talk about nano-technology.  The wood of a tree is comprised mostly of carbon -- with the cellulose of wood also containing some hydrogen, oxygen, and nitrogen.  The mass of wood also includes water.

Photosynthesis: Transforms Carbon Dioxide into Oxygen and a bit of Water -- AND CARBON!   

The answer is actually really simple: Carbon.  Photosynthesis is the act of converting CO2 from the air into O2 and a bit of H2O. 
It turns out that if you ask new Harvard graduates this question, the vast majority of them answer some variant of "It comes from the soil".  When people think of photosynthesis, they don't think about the carbon that's left behind.  They'll usually be puzzled as they answer, because in their hearts, they realize that "the soil" doesn't actually work as an answer, but they can't quite put all the pieces together.
If you ask 7th graders the same question right after they've finished their photosynthesis unit, they end up coming up with a variant of the same answer.  Or they say it comes from the water the plant absorbs. Soil and water have mass, and that seems to the determining factor in their answer.
Read more here: