( ( ( A ( second area ) ) ( of study ) ) ( ( concerns ( ( ( the ( oxygen-evolving complex ) ) ( in photosynthesis ) ) ( which ( is ( responsible ( for ( most ( of ( ( the oxygen ) ( in ( the atmosphere ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT A) (JJ second) (NN area)) (PP (IN of) (NP (NN study)))) (VP (VBZ concerns) (NP (NP (DT the) (JJ oxygen-evolving) (NN complex)) (PP (IN in) (NP (NN photosynthesis))) (SBAR (WHNP (WDT which)) (S (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (NP (NP (JJS most)) (PP (IN of) (NP (NP (DT the) (NN oxygen)) (PP (IN in) (NP (DT the) (NN atmosphere))))))))))))) (. .)))
A second area of study concerns the oxygen-evolving complex in photosynthesis which is responsible for most of the oxygen in the atmosphere.
(ROOT (S (NP (NP (DT The) (NN process)) (ADJP (JJ responsible) (PP (IN for) (NP (NP (DT the) (NN presence)) (PP (IN of) (NP (NP (NN oxygen)) (PP (IN in) (NP (PRP$ our) (NN atmosphere))))))))) (VP (VBZ is) (NP (NN photosynthesis))) (. .)))