Where do plants get their mass?

Question

Where does the mass of a plant come from?

Answer 1

Plants get their mass from carbon dioxide.
Plants take in water and carbon dioxide and usiing the energy from sunlight they make glucose (sugar).  This is 'food' for the plant which is stored as starch or used for builign materials like cellulose.  The molecular formula for glucose is C6H12O6 (6 molecules carbon, 12 hydrogen, 6 oxygen).  The carbon and oxygen in glucose come from carbon dioxide (CO2).  The hydrogen comes for water (H2O).  The oxygen from water is relased as a waste product as oxygen gas (O2).  If you look at the molecular weight of these atmos you will see that C = 12 amus, O = 16 amus, and H = 1 amu.  Therefore the mass of glucose is about 180 amus - 168 of that is from the C and O that came from carbon dioxide.  Water adds very little to the mass of the plant and plants DO NOT take up soil to add mass...that's why the amount of soil doesn't decrease in a potted plant.  Some 'nutrients' from soil are taken in, but this is a very small amount.