( ( ( ( ( ( The gills ) ( contain ( thousands ( of ( ( tiny capillaries ) ( -LRB- ( ( blood vessels ) -RRB- ) ) ) ) ) ) ) , ) so ) ( ( as ( water ( passes ( over ( the gills ) ) ) ) ) ( , ( oxygen ( is ( ( absorbed directly ) ( into ( the bloodstream ) ) ) ) ) ) ) ) . )
(ROOT (S (S (NP (DT The) (NNS gills)) (VP (VBP contain) (NP (NP (NNS thousands)) (PP (IN of) (NP (NP (JJ tiny) (NNS capillaries)) (PRN (-LRB- -LRB-) (NP (NN blood) (NNS vessels)) (-RRB- -RRB-))))))) (, ,) (IN so) (S (SBAR (IN as) (S (NP (NN water)) (VP (VBZ passes) (PP (IN over) (NP (DT the) (NNS gills)))))) (, ,) (NP (NN oxygen)) (VP (VBZ is) (VP (VBN absorbed) (ADVP (RB directly)) (PP (IN into) (NP (DT the) (NN bloodstream)))))) (. .)))
The gills contain thousands of tiny capillaries (blood vessels), so as water passes over the gills, oxygen is absorbed directly into the bloodstream.
(ROOT (S (NP (NNP Oxygen)) (VP (VBZ is) (VP (VBN transferred) (PP (IN through) (NP (NNS capillaries))))) (. .)))