( ( ( The ( main function ) ) ( of ( the ER ) ) ) ( ( is ( to ( ( transport materials ) ( through ( the cell ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ main) (NN function)) (PP (IN of) (NP (DT the) (NNP ER)))) (VP (VBZ is) (S (VP (TO to) (VP (VB transport) (NP (NNS materials)) (PP (IN through) (NP (DT the) (NN cell))))))) (. .)))
The main function of the ER is to transport materials through the cell.
(ROOT (S (NP (NP (DT The) (JJ main) (NN function)) (PP (IN of) (NP (DT the) (JJ circulatory) (NN system)))) (VP (VBZ is) (S (VP (TO to) (VP (VB transport) (NP (NNS materials)))))) (. .)))