If you know the reaction of photosynthesis (CO^2+H^2O>C^6H^12O^6+O^2) Then you know cellular respiration. Because you just flip the whole equation around from photosynthesis and then you have cellular respiration.
If he studied a small sample it wouldn't be a representative sample. since he got such a large sample there is a chance most likely all organisms follow the rules of evolution.
