( They ( ( are ( ( complex molecules ) ( required ( for ( ( the ( structure ( , ( ( function and ) regulation ) ) ) ) ( of ( ( the ( body 's ) ) ( cells ( , ( ( tissues and ) organs ) ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (PRP They)) (VP (VBP are) (NP (NP (JJ complex) (NNS molecules)) (VP (VBN required) (PP (IN for) (NP (NP (DT the) (NN structure) (, ,) (NN function) (CC and) (NN regulation)) (PP (IN of) (NP (NP (DT the) (NN body) (POS 's)) (NNS cells) (, ,) (NNS tissues) (CC and) (NNS organs)))))))) (. .)))
They are complex molecules required for the structure, function and regulation of the body's cells, tissues and organs.
(ROOT (S (NP (DT The) (NN sequence) (NN cell) (CD →) (NN tissue) (CD →) (NN organ) (CD →) (NN organ) (NN system)) (VP (VBZ identifies) (NP (NP (DT the) (NNS levels)) (PP (IN of) (NP (NP (NN organization)) (PP (IN of) (NP (NP (NN body) (NNS structures)) (PP (IN in) (NP (DT a) (NN human)))))))) (PP (IN from) (NP (NP (JJS simplest)) (PP (TO to) (NP (JJS most) (NN complex)))))) (. .)))
The sequence cell → tissue → organ → organ system identifies the levels of organization of body structures in a human from simplest to most complex.