( ( ( -LRB- ( ( ( Oxygen and ) energy ) -RRB- ) ) ( When ( plants photosynthesize ) ) ) ( , ( they ( ( ( give off ) oxygen ) . ) ) ) )
(ROOT (S (S (ADJP (ADJP (-LRB- -LRB-) (NP (QP (NP (NNP Oxygen)) (CC and) (NP (NN energy)))) (-RRB- -RRB-)) (SBAR (WHADVP (WRB When)) (S (NP (NNS plants)) (VP (VBP photosynthesize)))))) (, ,) (NP (PRP they)) (VP (VBP give) (PRT (RP off)) (NP (NN oxygen))) (. .)))
(Oxygen and energy) When plants photosynthesize, they give off oxygen.
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN given) (PRT (RP off)) (PP (IN by) (NP (NNS plants))))) (. .)))