( ( Circadian rhythms ) ( ( are ( ( ( biological rhythms ) ( with ( ( an ( intrinsic period ) ) ( of ( ( approximately 24 ) hours ) ) ) ) ) ( that ( are ( driven ( by ( ( an ( endogenous pacemaker ) ) ( in ( ( ( the ( suprachiasmatic nuclei ) ) ( -LRB- ( SCN -RRB- ) ) ) ( of ( the hypothalamus ) ) ) ) ) ) ) ) ) ) ) ; ) )
(ROOT (S (NP (NN Circadian) (NNS rhythms)) (VP (VBP are) (NP (NP (JJ biological) (NNS rhythms)) (PP (IN with) (NP (NP (DT an) (JJ intrinsic) (NN period)) (PP (IN of) (NP (QP (RB approximately) (CD 24)) (NNS hours))))) (SBAR (WHNP (WDT that)) (S (VP (VBP are) (VP (VBN driven) (PP (IN by) (NP (NP (DT an) (JJ endogenous) (NN pacemaker)) (PP (IN in) (NP (NP (NP (DT the) (JJ suprachiasmatic) (NN nuclei)) (PRN (-LRB- -LRB-) (NP (NNP SCN)) (-RRB- -RRB-))) (PP (IN of) (NP (DT the) (NNS hypothalamus))))))))))))) (: ;)))
Circadian rhythms are biological rhythms with an intrinsic period of approximately 24 hours that are driven by an endogenous pacemaker in the suprachiasmatic nuclei (SCN) of the hypothalamus;
(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))))) (. .)))