( O ( ( ( Organ ( ( A group ) ( of ( tissues ( which ( ( work together ) ( as ( a ( single unit ) ) ) ) ) ) ) ) ) ( to ( ( perform ( a ( particular function ) ) ) ( within ( a ( multicellular organism ) ) ) ) ) ) . ) )
(ROOT (S (NP (NNP O)) (VP (VBN Organ) (NP (NP (DT A) (NN group)) (PP (IN of) (NP (NP (NNS tissues)) (SBAR (WHNP (WDT which)) (S (VP (VBP work) (ADVP (RB together)) (PP (IN as) (NP (DT a) (JJ single) (NN unit))))))))) (S (VP (TO to) (VP (VB perform) (NP (DT a) (JJ particular) (NN function)) (PP (IN within) (NP (DT a) (NN multicellular) (NN organism))))))) (. .)))
O Organ A group of tissues which work together as a single unit to perform a particular function within a multicellular organism.
(ROOT (S (SBAR (WHADVP (WRB When)) (S (NP (NP (JJ different) (NNS types)) (PP (IN of) (NP (NNS tissues)))) (VP (VBP work) (ADVP (RB together)) (S (VP (TO to) (VP (VB perform) (NP (DT a) (JJ unique) (NN function)))))))) (, ,) (NP (PRP they)) (VP (VBP form) (NP (NN organ))) (. .)))