( Calcium ( ( is ( absorbed ( ( ( ( by ( ( ( active transport ) , ) ( which ( requires energy ) ) ) ) , ) and ) ( by ( passive diffusion ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Calcium)) (VP (VBZ is) (VP (VBN absorbed) (PP (PP (IN by) (NP (NP (JJ active) (NN transport)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ requires) (NP (NN energy))))))) (, ,) (CC and) (PP (IN by) (NP (JJ passive) (NN diffusion)))))) (. .)))
Calcium is absorbed by active transport, which requires energy, and by passive diffusion.
(ROOT (S (SBAR (IN Because) (S (S (NP (DT the) (NN solute)) (VP (VBZ is) (VP (VBG moving) (PRT (RP down)) (NP (DT the) (NN concentration) (NN gradient))))) (, ,) (CC and) (S (NP (NP (DT no) (NN input)) (PP (IN of) (NP (NN energy)))) (VP (VBZ is) (VP (VBN required)))))) (, ,) (NP (JJ facilitated) (NN diffusion)) (VP (VBZ is) (VP (VBN considered) (NP (NP (DT a) (-LRB- -LRB-) (NN n) (-RRB- -RRB-) (JJ passive) (NN type)) (PP (IN of) (NP (NN transport)))))) (. .)))