( ( ( The ( first organisms ) ) ( to ( appear ( on ( the planet ) ) ) ) ) ( ( were ( ( bacteria , ) ( which ( are ( single-celled prokaryotes ) ) ) ) ) . ) )
(ROOT (S (NP (NP (DT The) (JJ first) (NNS organisms)) (SBAR (S (VP (TO to) (VP (VB appear) (PP (IN on) (NP (DT the) (NN planet)))))))) (VP (VBD were) (NP (NP (NNS bacteria)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBP are) (NP (JJ single-celled) (NNS prokaryotes))))))) (. .)))
The first organisms to appear on the planet were bacteria, which are single-celled prokaryotes.
(ROOT (S (NP (DT A) (JJ single-celled) (NN prokaryotic)) (VP (VBZ is) (NP (DT a) (NNS bacteria))) (. .)))