( ( One ( of ( ( the materials ) ( that ( plants ( produce ( as ( they ( make food ) ) ) ) ) ) ) ) ) ( ( is ( oxygen gas ) ) . ) )
(ROOT (S (NP (NP (CD One)) (PP (IN of) (NP (NP (DT the) (NNS materials)) (SBAR (IN that) (S (NP (NNS plants)) (VP (VBP produce) (SBAR (IN as) (S (NP (PRP they)) (VP (VBP make) (NP (NN food))))))))))) (VP (VBZ is) (NP (NN oxygen) (NN gas))) (. .)))
One of the materials that plants produce as they make food is oxygen gas.
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN given) (PRT (RP off)) (PP (IN by) (NP (NNS plants))))) (. .)))