( it ( ( ( eats plants ) only ) . ) )
(ROOT (S (NP (PRP it)) (VP (VBZ eats) (NP (NNS plants)) (ADVP (RB only))) (. .)))
it eats plants only.
(ROOT (S (NP (DT The) (NN heterotroph)) (VP (VBZ eats) (NP (UCP (ADJP (JJ only)) (CC or) (ADVP (RB mainly))) (NNS plants))) (. .)))