As you point out, plants break down the water molecules to produce the oxygen, but the CO2 is the fuel used for that process, just as my engine produces torque by using a combination of fuel (gasoline or diesel) and air.
You can choose a DNA without a subscription to the Ancestry.com service, a DNA test with a subscription to U.S. discovery service or a DNA test with World explorer. Once you choose an option, Ancestry.com will ship you a test kit. The test kit has a small mouth swab which you wipe on the inside of your mouth.
Family Tree DNA offers the analysis of mitochondrial DNA, which is found in both men and women. mtDNA traces the matrilineal all-female line. Family Tree DNA offers testing of the HVR1 region, HVR2 region, and the Full Mitochondrial Sequence (FMS) which sequences the entire mitochondrial genome.