( Cells ( ( contain ( ( ( a ( single ( polar flagellum ) ) ) , ) ( so ( are motile ) ) ) ) . ) )
(ROOT (S (NP (NNS Cells)) (VP (VBP contain) (NP (NP (DT a) (JJ single) (JJ polar) (NN flagellum)) (, ,) (SBAR (IN so) (S (VP (VBP are) (ADJP (JJ motile))))))) (. .)))
Cells contain a single polar flagellum, so are motile.
(ROOT (S (PP (IN In) (NP (NNS humans))) (, ,) (NP (DT the) (NN sperm) (NN cell)) (VP (VBZ is) (NP (NP (DT the) (JJ only) (NN cell)) (PP (IN with) (NP (DT the) (NN flagella) (NN structure))) (SBAR (WHNP (WDT that)) (S (VP (VBZ enables) (ADVP (RB motility))))))) (. .)))