( ( Healthy plants ) ( ( ( give off ) ( oxygen ( during photosynthesis ) ) ) . ) )
(ROOT (S (NP (JJ Healthy) (NNS plants)) (VP (VBP give) (PRT (RP off)) (NP (NP (NN oxygen)) (PP (IN during) (NP (NN photosynthesis))))) (. .)))
Healthy plants give off oxygen during photosynthesis.
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN given) (PRT (RP off)) (PP (IN by) (NP (NNS plants))))) (. .)))