Time Structure of the Functional Organization of Living System

**15**

the neighboring atmosphere [3, 4].

**Chapter 2**

**Abstract**

applied topics.

**1. Introduction**

Perspectives

Chronobiology and Its General

As a significance of the earth's rotation about its axis approximately every 24 hours, most organisms on this planet are subjected to probable variations of light and temperature. A diverse range of species, from cyanobacteria to humans, evolved internal biological clocks that allow for the anticipation of these daily variations. The field of chronobiology, the study of the rhythms in plants and animals, was limited to botanists for centuries. Only recently during the last decades, the research was expanded to include animals and later even human beings. Rhythms have been recognized and associated to the fluctuation of day and night and to the succession of the seasons. Nowadays, chronobiology has developed into a multidisciplinary field in which scientists are involved in basic research as well as in

**Keywords:** chronobiology, circadian rhythm, infradian, ultradian, chronophysiology

Most organisms on this planet are subject to the significance of earth's rotation around its axis, approximately every 24 hours, for probable variations of light and temperature. A vast range of species, from cyanobacteria to human beings, evolved internal biological clocks that permit for the eagerness of these daily variations. Thus, physiology and functions of an organism are primarily intertwined with this geophysical cycle. An astronomer in 1729, whose name was Jean-Jacques d'Ortousde Mairan presented early impending into this evolutionary relationship between inner physiology and the geophysical cycle, he reported that daily leaf activities in heliotrope plants persist in constant darkness [1]. In 1959, another scientist whose name was Franz Halberg give emphasis to the endogenous nature of biological clocks and coined the term circadian, that refer to daily rhythms which are truly endogenously generated, i.e., rhythms having a time period of about 24 hours that continue to vary in the absence of any environmental input [2]. The term circadian comes from the Latin *circa*, meaning "around" and *dies*, "day," meaning "approximately a day." It is regulated by circadian clocks. A recognized intrinsic property of single cells has been named as rhythm making, which was determined by an intracellular molecular oscillator based on transcriptional/post translational negative response loops. Endogenous variations are synchronized to the environment under common conditions, and is usually considered that biological clock present an adaptive advantage by guarantying that internal biochemical and physiological progression of an organism's in accumulation to actions, are optimally tailored to

*Mohammad Rayees Dar and Abdul Roof Rather*
