( It ( ( ( is ( in ( ( the area ) ( of ( the ( small intestine ) ) ) ) ) ) ( that ( ( ( the ( ( most essential ) functions ) ) ( of ( ( digestion and ) absorption ) ) ) occur ) ) ) . ) )
(ROOT (S (NP (PRP It)) (VP (VBZ is) (PP (IN in) (NP (NP (DT the) (NN area)) (PP (IN of) (NP (DT the) (JJ small) (NN intestine))))) (SBAR (IN that) (S (NP (NP (DT the) (ADJP (RBS most) (JJ essential)) (NNS functions)) (PP (IN of) (NP (NN digestion) (CC and) (NN absorption)))) (VP (VBP occur))))) (. .)))
It is in the area of the small intestine that the most essential functions of digestion and absorption occur.
(ROOT (S (NP (NP (JJS Most)) (PP (IN of) (NP (DT the) (NN digestion) (NNS reactions)))) (VP (VBP occur) (PP (IN in) (NP (DT the) (JJ small) (NN intestine)))) (. .)))