( ( Oxygen gas ) ( ( is ( ( returned ( to ( ( the atmosphere ) ( from ( the ( living world ) ) ) ) ) ) ( by ( ( ( green ( plants ( and ( cyan bacteria ) ) ) ) , ) ( which ( ( give out ) ( oxygen ( during photosynthesis ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN Oxygen) (NN gas)) (VP (VBZ is) (VP (VBN returned) (PP (TO to) (NP (NP (DT the) (NN atmosphere)) (PP (IN from) (NP (DT the) (NN living) (NN world))))) (PP (IN by) (NP (NP (JJ green) (NNS plants) (CC and) (NN cyan) (NNS bacteria)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP give) (PRT (RP out)) (NP (NP (NN oxygen)) (PP (IN during) (NP (NN photosynthesis))))))))))) (. .)))
Oxygen gas is returned to the atmosphere from the living world by green plants and cyan bacteria, which give out 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))))) (. .)))