( metabolism ( ( refers ( to ( all ( of ( ( the ( chemical reaction ) ) ( that ( occur ( within ( an organism ) ) ) ) ) ) ) ) ) . ) )
(ROOT (S (NP (NN metabolism)) (VP (VBZ refers) (PP (TO to) (NP (NP (DT all)) (PP (IN of) (NP (NP (DT the) (JJ chemical) (NN reaction)) (SBAR (WHNP (WDT that)) (S (VP (VBP occur) (PP (IN within) (NP (DT an) (NN organism))))))))))) (. .)))
metabolism refers to all of the chemical reaction that occur within an organism.
(ROOT (S (NP (NP (DT The) (NN sum)) (PP (IN of) (NP (NP (DT all) (JJ chemical) (NNS reactions)) (SBAR (WHNP (WDT that)) (S (VP (VBP take) (NP (NN place)) (PP (IN within) (NP (DT an) (NN organism))))))))) (VP (VBZ is) (VP (VBN known) (PP (IN as) (NP (NN metabolism))))) (. .)))
The sum of all chemical reactions that take place within an organism is known as metabolism.