( ( ( ( ( ( Some ( of ( the ( photosynthetic species ) ) ) ) ( have ( pigments ( ( ( similar ( to chlorophyll ) ) a ) ( in ( higher plants ) ) ) ) ) ) , ) but ) ( they ( ( do not ) ( ( produce oxygen ) ( as ( ( a by-product ) ( of photosynthesis ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (NP (DT Some)) (PP (IN of) (NP (DT the) (JJ photosynthetic) (NN species)))) (VP (VBP have) (VP (VBZ pigments) (NP (NP (ADJP (JJ similar) (TO to) (JJ chlorophyll)) (DT a)) (PP (IN in) (NP (JJR higher) (NNS plants))))))) (, ,) (CC but) (S (NP (PRP they)) (VP (VBP do) (RB not) (VP (VB produce) (NP (NN oxygen)) (PP (IN as) (NP (NP (DT a) (NN by-product)) (PP (IN of) (NP (NN photosynthesis)))))))) (. .)))
Some of the photosynthetic species have pigments similar to chlorophyll a in higher plants, but they do not produce oxygen as a by-product of photosynthesis.
(ROOT (S (PP (IN On) (NP (DT a) (JJ global) (NN scale))) (, ,) (NP (NP (NNS plants)) (CC and) (NP (JJ other) (JJ photosynthetic) (NNS organisms))) (VP (VBP have) (VP (VBN generated) (NP (NP (DT all)) (PP (IN of) (NP (NP (DT the) (NN oxygen)) (PP (IN in) (NP (DT the) (NN air)))))))) (. .)))
On a global scale, plants and other photosynthetic organisms have generated all of the oxygen in the air.