( ( ( ( ( ( In ( ( normal ( aerobic metabolism ) ) ( by ( ( plants and ) animals ) ) ) ) ( ( the acids ) ( are ( oxidized ( to ( ( carbon dioxide ) ( plus ( chemical energy ) ) ) ) ) ) ) ) , ) but ) ( ( in ( ( the absence ) ( of oxygen ) ) ) ( ( the acids ) accumulate ) ) ) . )
(ROOT (S (S (PP (IN In) (NP (NP (JJ normal) (JJ aerobic) (NN metabolism)) (PP (IN by) (NP (NNS plants) (CC and) (NNS animals))))) (NP (DT the) (NNS acids)) (VP (VBP are) (VP (VBN oxidized) (PP (TO to) (NP (NP (NN carbon) (NN dioxide)) (PP (CC plus) (NP (NN chemical) (NN energy)))))))) (, ,) (CC but) (S (PP (IN in) (NP (NP (DT the) (NN absence)) (PP (IN of) (NP (NN oxygen))))) (NP (DT the) (NNS acids)) (VP (VBP accumulate))) (. .)))
In normal aerobic metabolism by plants and animals the acids are oxidized to carbon dioxide plus chemical energy, but in the absence of oxygen the acids accumulate.
(ROOT (S (NP (NNP Carbon) (NN dioxide)) (ADVP (RB chemically)) (VP (VBP weather) (NP (NNS rocks)) (PP (IN by) (S (VP (VBG creating) (NP (NNS acids)))))) (. .)))