( ( The plant ) ( ( ( gives off ) ( oxygen ( for ( the ( fish ( to use ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN plant)) (VP (VBZ gives) (PRT (RP off)) (NP (NP (NN oxygen)) (PP (IN for) (NP (DT the) (NN fish) (S (VP (TO to) (VP (VB use)))))))) (. .)))
The plant gives off oxygen for the fish to use.
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN given) (PRT (RP off)) (PP (IN by) (NP (NNS plants))))) (. .)))