A biological cycle, or rhythm, that is approximately 24 hours long is called a(n) ________ cycle.
A) infradian
B) circadian
C) diurnal
D) ultradian

Question

A biological cycle, or rhythm, that is approximately 24 hours long is called a(n) ________ cycle.
A) infradian 
B) circadian 
C) diurnal
D) ultradian

Quizplus · Accepted Answer

A circadian cycle is a biological rhythm that repeats approximately every 24 hours. Infradian rhythms have a longer cycle, such as a monthly menstrual cycle, while ultradian rhythms have a shorter cycle, such as the sleep cycles that occur throughout the night. Diurnal refers to an organism that is active during the day and resting at night, but it does not necessarily specify a 24-hour rhythm. Therefore, the best choice is B, circadian.

A Biological Cycle, or Rhythm, That Is Approximately 24 Hours