( ( Animal cells ) ( ( lack ( ( the ( rigid ( cell walls ) ) ) ( that ( characterize ( plant cells ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Animal) (NNS cells)) (VP (VBP lack) (NP (NP (DT the) (JJ rigid) (NN cell) (NNS walls)) (SBAR (WHNP (WDT that)) (S (VP (VBP characterize) (NP (NN plant) (NNS cells))))))) (. .)))
Animal cells lack the rigid cell walls that characterize plant  cells.
(ROOT (S (NP (NNP Plant) (NNS cells)) (VP (VBP have) (NP (NP (NNS structures)) (SBAR (WHNP (WDT that) (NN animal) (NNS cells)) (S (VP (VBP lack)))))) (. .)))