In the Noble Qur’an, wherever the word ‘Sign(s)’ is used it reveals that something is going to be known for the guidance of those who contemplate over the mysteries of contents in that verse. That is why along with the word sign, people of understanding, people who contemplate, mindful soul, and people of knowledge is more often used through out this Divine Book of guidance. As an example we read in Qur’an as;
(إِنَّ فِي خَلْقِ السَّمَاوَاتِ وَالأَرْضِ وَاخْتِلاَفِ اللَّيْلِ وَالنَّهَارِ لآيَاتٍ لِّأُوْلِي الألْبَابِ) آل عمران190
“And in the alteration of night and day, and the food We send down from the sky, and revives therewith the earth after its death, and in the turning about of winds are signs for people of understanding”.(45:4-5).
A focus on the first part of the verse from Qur’an, Allah calls the attention of mankind to the alteration of day and night and all changes it brings along as signs for a mindful soul in understanding Allah. The insight knowledge in the alteration of day and night might count on numerous fields of science together if taken into account. In the field of Biology and Botany for instance, this phenomenon of light and dark period is explained in terms of photoperiod or Photoperiodism and explain the biological response of organisms around the world to the level of dark and light periods for initiation of growth, egg production and flowering. Many flowering plants use a photoreceptor protein, such as phytochrome or cryptochrome, as signals for these seasonal changes in the length of day and night to initiate flowering. For example, when the days are getting longer, the tree might start to produce buds and blooms, since it would sense that spring is on the way. As days shorten, the plant would start to become dormant, producing seeds for next year and taking steps to ensure that it would be ready for winter. This knowledge of photoperiodism in plants has allowed botanists to trick plants grown in greenhouse by manipulating light levels for bloom and seed production at higher prices. It is this alteration of day and night (light: dark) periods, we have various foods available during different season and different areas of the world. Thus the great sign in the alteration of day and night as Qur’n revealed has enabled our sustenance as a ‘Sign” for knowing Allah and guided us to manipulate this process for more production.
Another related term explaining this phenomenon in the field of life science and biology is circadian rhythm. It is considered as an internal biological clock of 24-hour cycle in the biochemical, physiological or behavioral processes of all living entities enabling then to do perform certain actions during this time of 24 hrs. Living things start or stop production of various hormones/ chemicals in response to the turning on and off process of this rhythm. The initiation of day light (dawn) has very strong influence in this turning on and off sessions of internal biological clock. Animals including birds and insects may wake up from sleep or diapauses and prepare for various actions related to their survival. How magnificently all the Knowing has informed us! “He causes the dawn to break; and He has made the night for rest, and the sun and the moon for reckoning (of time); this is an arrangement of the Mighty, the Knowing.” (Qur’an 6: 96)
Allah causes dawn to break what? To break this internal clock of 24 hours cycle with help of dawn or day light. Allah almighty, made night repose, rest time or a break time and day for activities. There are specific biochemical reactions that take place either in dark or in light periods. Plants, for instance, prepare to produce phytochrome or cryptochrome in response to light signals. The light dependent process of photosynthesis in which solar energy is harvested and transferred into the chemical bonds of ATP(adenosine triphosphate); can occur only in light as the dawn approaches and glow of light reaches plants. The dark reaction or light-independent reactions produce carbohydrates by using ATP and NADPH that was formed during day time. Evapo- transpiration is accelerated as the temperature rises. In the afternoon, photosynthesis slows down and respiration increases. At night time, as the temperature falls, transpiration in plants slows down and energy reserves are utilized in the formation of compounds. Most plants would die if just one night failed to take place. From this point of view, night means rest and reinvigoration for plants, just as it does for human beings. In human beings the hormone melatonin, secrets at night, prepares the body for sleep by slowing down peoples' physical movements and eases their minds making them sleepy. During sleep, heartbeat respiration, and blood pressure falls down. In the morning, the production of these hormones stops and the body is again stimulated for work. At the same time, sleep allows the body's muscles and tissues to repair themselves and enable the body to replace old or dead cells. As energy expenditure is reduced during sleep, the body starts storing energy throughout the night. Several chemicals vital for the immune system and growth hormones are also secreted during sleep or rest time.
1.The Noble Qur’an, chapter 3, verse 190, chapter 10 verse 67, chapter 25, verse 47, and chapter 78 verses 09-10 (Tanzil : Quran Navigator)
2.Fendrri, ‘night and day, a sign for the mindful’ Reflecting on the Qur,an http://understandingthequran.blogspot.com/2009/02/night-and-day-sign-for-mindful.html
3.Harun Yahya, ‘reduced movement at night’ Scientific miracle in Qur’an, http://www.miraclesofthequran.com/scientific_84.html#dp