Circadian rhythm refers to
a) the pattern of emotional ups and downs we routinely experience.
b) a pattern of biological functioning that occurs on a 24-hour cycle.
c) the experience of sleep apnea following paradoxical sleep.
d) the cycle of four distinct stages that we experience during a normal night's sleep

The correct option is B) a pattern of biological functioning that occurs on a 24-hour cycle.

Explanation:

Biological rhythm is defined as the regular variation of an organic function related to the course of time, circadian biological phenomena (around the day), are those with a period of approximately 24 hours.

Circadian rhythms are physical, mental and behavioral changes that follow a daily cycle (the biological rhythm), and that respond primarily to light and darkness in an organism's environment. This cycle close to 24 hours, allows to recognize the sleep-wake phenomena and their homeostatic action, in the systemic processes of every living being. The circadian system is composed of photoreceptors, pacemakers and efferent pathways that allow a regular functioning of the sleep and wakeful state.

organ system-an organ system is a group of organs that work together to perform one or more functions. each does a particular job in the body, and is made up of certain tissues.