( ( If ( oxygen ( ( is not ) available ) ) ) ( , ( ( organic molecules ) ( ( may ( be ( used ( as ( ( ( the ( final ( electron acceptor ) ) ) ( in ( a process ) ) ) ( called ( ( fermentation , ) ( which ( produces ( ( ( carbon dioxide ) and ) ( ( an ( organic molecule ) ) ( -LRB- ( ( often ethanol ) -RRB- ) ) ) ) ) ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (SBAR (IN If) (S (NP (NN oxygen)) (VP (VBZ is) (RB not) (ADJP (JJ available))))) (, ,) (NP (JJ organic) (NNS molecules)) (VP (MD may) (VP (VB be) (VP (VBN used) (SBAR (IN as) (S (NP (NP (DT the) (JJ final) (NN electron) (NN acceptor)) (PP (IN in) (NP (DT a) (NN process)))) (VP (VBD called) (NP (NP (NN fermentation)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ produces) (NP (NP (NN carbon) (NN dioxide)) (CC and) (NP (NP (DT an) (JJ organic) (NN molecule)) (PRN (-LRB- -LRB-) (NP (RB often) (NN ethanol)) (-RRB- -RRB-)))))))))))))) (. .)))
If oxygen is not available, organic molecules may be used as the final electron acceptor in a process called fermentation, which produces carbon dioxide and an organic molecule (often ethanol).
(ROOT (S (NP (NNP Fermentation)) (VP (VBZ is) (NP (NP (DT the) (NN process)) (PP (IN of) (S (VP (VBG making) (NP (NN atp)) (PP (IN without) (NP (NN oxygen)))))))) (. .)))