( Therefore ( , ( ( ( circadian rhythms ) ( in nature ) ) ( ( are ( related ( to ( ( the ( day-night cycle ) ) ( which ( occurs ( every ( 24 hours ) ) ) ) ) ) ) ) . ) ) ) )
(ROOT (S (ADVP (RB Therefore)) (, ,) (NP (NP (NN circadian) (NNS rhythms)) (PP (IN in) (NP (NN nature)))) (VP (VBP are) (ADJP (VBN related) (PP (TO to) (NP (NP (DT the) (JJ day-night) (NN cycle)) (SBAR (WHNP (WDT which)) (S (VP (VBZ occurs) (NP (DT every) (CD 24) (NNS hours))))))))) (. .)))
Therefore, circadian rhythms in nature are related to the day-night cycle which occurs every 24 hours.
(ROOT (S (NP (NP (JJ Regular) (NNS changes)) (PP (IN in) (NP (NN biology) (CC or) (NN behavior))) (SBAR (WHNP (WDT that)) (S (VP (VBP occur) (PP (IN in) (NP (DT a) (CD 24) (NN hour) (NN cycle))))))) (VP (VBP are) (NP (NP (NN part)) (PP (IN of) (NP (DT the) (NN circadian) (NN rhythm))))) (. .)))