( Protists ( ( are ( ( ( single-celled eukaryotes ) , ) ( which ( are ( organisms ( with ( a nucleus ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNS Protists)) (VP (VBP are) (NP (NP (JJ single-celled) (NNS eukaryotes)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (NP (NP (NNS organisms)) (PP (IN with) (NP (DT a) (NN nucleus))))))))) (. .)))
Protists are single-celled eukaryotes, which are organisms with a nucleus.
(ROOT (S (NP (JJ Many) (NNS scientists)) (VP (VBP think) (SBAR (S (NP (NNS protists)) (VP (VBP are) (NP (DT the) (JJS oldest) (NNS eukaryotes)))))) (. .)))