( ( Only ( dissolved oxygen ) ) ( ( contributes ( to ( ( the tension ) ( -LRB- ( or ( ( partial pressure ) -RRB- ) ) ) ) ) ) . ) )
(ROOT (S (NP (RB Only) (JJ dissolved) (NN oxygen)) (VP (VBZ contributes) (PP (TO to) (NP (NP (DT the) (NN tension)) (PRN (-LRB- -LRB-) (CC or) (NP (NP (JJ partial)) (NP (NN pressure))) (-RRB- -RRB-))))) (. .)))
Only dissolved oxygen contributes to the tension (or partial pressure).
(ROOT (S (NP (NNS Plants)) (VP (CONJP (RB not) (JJ only)) (VP (VBP contribute) (NP (NN food))) (CC but) (VP (VBD oxygen) (PP (IN for) (NP (NNS organisms))))) (. .)))