Assalamu alaikum wa rehmatullahi wa barakatuh
And He subjected for you the sun and the moon, continuous [in orbit], and subjected for you the night and the day.(Surah Ibrahim 33)
A circadian rhythm is any biological process that displays an endogenous oscillation of about 24 hours. These rhythms are driven by a circadian clock, and rhythms have been widely observed in plants, animals,fungi and cyanobacteria.
The circadian clock and thus the circadian rhythm is controlled by the sun and moon and by the alteration of days and nights.Some of the biological processes controlled are enlisted below.
The level of alertness,
Production of Hormones
All are effected by the movement of sun outside,and the day and night times,all are coordinated by the circadian rhythm…Alhmdulillah,masha Allahu laa quwwata illa billah.
Now regarding plants:
Light is the signal by which plants synchronize their internal clocks to their environment and is sensed by a wide variety of photoreceptors. Red and blue light are absorbed through several phytochromes and cryptochromes. One phytochrome, phyA, is the main phytochrome in seedlings grown in the dark but rapidly degrades in light to produce Cry1. Phytochromes B–E are more stable with phyB, the main phytochrome in seedlings grown in the light. The cryptochrome (cry) gene is also a light-sensitive component of the circadian clock and is thought to be involved both as a photoreceptor and as part of the clock’s endogenous pacemaker mechanism. Cryptochromes 1–2 (involved in blue–UVA) help to maintain the period length in the clock through a whole range of light conditions
Plants are the producers of food,and they produce food in the presence of sunlight,by the process of photosynthesis.
They continue their other processes in the absence of sunlight,ie in the dark.Both,the presence of sunlight,as well as the absence are needed for a normal life of a producer..!!!
Say, “Have you considered: if Allah should make for you the night continuous until the Day of Resurrection, what deity other than Allah could bring you light? Then will you not hear?”Say, “Have you considered: if Allah should make for you the day continuous until the Day of Resurrection, what deity other than Allah could bring you a night in which you may rest? Then will you not see?”(28:71-72)