( ( Circadian rhythms ) ( ( ( ( ( are ( tied ( to ( ( the ( 24-hour cycle ) ) ( of ( ( the ( earth 's ) ) rotation ) ) ) ) ) ) and ) ( are ( ( possibly ( a result ) ) ( of ( ( changing amounts ) ( of ( ( light and ) darkness ) ) ) ) ) ) ) ( as ( ( the day ) progresses ) ) ) . ) )
(ROOT (S (NP (NN Circadian) (NNS rhythms)) (VP (VP (VBP are) (VP (VBN tied) (PP (TO to) (NP (NP (DT the) (JJ 24-hour) (NN cycle)) (PP (IN of) (NP (NP (DT the) (NN earth) (POS 's)) (NN rotation))))))) (CC and) (VP (VBP are) (NP (NP (RB possibly) (DT a) (NN result)) (PP (IN of) (NP (NP (JJ changing) (NNS amounts)) (PP (IN of) (NP (NN light) (CC and) (NNS darkness))))))) (SBAR (IN as) (S (NP (DT the) (NN day)) (VP (VBZ progresses))))) (. .)))
Circadian rhythms are tied to the 24-hour cycle of the earth's rotation and are possibly a result of changing amounts of light and darkness as the day progresses.
(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))))) (. .)))