( Y ( ( Yeast ( ( Single-celled micro-organism ) ( which ( brings ( about fermentation ) ) ) ) ) . ) )
(ROOT (S (NP (NNP Y)) (VP (VBZ Yeast) (NP (NP (JJ Single-celled) (NN micro-organism)) (SBAR (WHNP (WDT which)) (S (VP (VBZ brings) (PP (IN about) (NP (NN fermentation)))))))) (. .)))
Y Yeast Single-celled micro-organism which brings about fermentation.
(ROOT (S (NP (NNP Single-celled)) (VP (VBP are) (ADJP (JJ yeasts))) (. .)))