( They ( ( ( do this ) ( by ( directly ( interacting ( ( ( ( with ( extracellular molecules ) ) ( -LRB- ( receptors -RRB- ) ) ) or ) ( by ( ( facilitating ( ( the movement ) ( of ( ( ions or ) ( other substances ) ) ) ) ) ( across ( ( cell membranes ) ( -LRB- ( ( ( ( ion channels ) and ) ( transport proteins ) ) -RRB- ) ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP do) (NP (DT this)) (PP (IN by) (S (ADVP (RB directly)) (VP (VBG interacting) (PP (PP (IN with) (NP (NN extracellular) (NNS molecules))) (PRN (-LRB- -LRB-) (VB receptors) (-RRB- -RRB-)) (CC or) (PP (IN by) (S (VP (VBG facilitating) (NP (NP (DT the) (NN movement)) (PP (IN of) (NP (NP (NNS ions)) (CC or) (NP (JJ other) (NNS substances))))) (PP (IN across) (NP (NP (NN cell) (NNS membranes)) (PRN (-LRB- -LRB-) (NP (NP (NN ion) (NNS channels)) (CC and) (NP (NN transport) (NNS proteins))) (-RRB- -RRB-)))))))))))) (. .)))
They do this by directly interacting with extracellular molecules (receptors) or by facilitating the movement of ions or other substances across cell membranes (ion channels and transport proteins).
(ROOT (S (NP (DT The) (NN term) (JJ passive) (NN transport)) (VP (VBZ describes) (NP (DT a) (NN way)) (SBAR (IN that) (S (NP (JJ small) (NNS molecules) (CC or) (NNS ions)) (VP (VBP move) (PP (IN across) (NP (NP (DT the) (NN cell)) (VP (VBN membrane) (PP (IN without) (NP (NP (NN input)) (PP (IN of) (NP (NN energy))))) (PP (IN by) (NP (DT the) (NN cell)))))))))) (. .)))