( ( The spleen ) ( ( is ( responsible ( for ( removing ( old ( red ( blood cells ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (DT The) (NN spleen)) (VP (VBZ is) (ADJP (JJ responsible) (PP (IN for) (S (VP (VBG removing) (NP (JJ old) (JJ red) (NN blood) (NNS cells))))))) (. .)))
The spleen is responsible for removing old red blood cells.
(ROOT (S (NP (NP (DT The) (JJ main) (NN function)) (PP (IN of) (NP (DT the) (NN spleen)))) (VP (VBZ is) (S (VP (TO to) (VP (VP (VB filter) (NP (DT the) (NN blood))) (CC and) (VP (VB remove) (NP (JJ unwanted) (JJ red) (NN blood) (NNS cells))))))) (. .)))
The main function of the spleen is to filter the blood and remove unwanted red blood cells.