Electronic Waste It has been known since ancient times that certain plants regularly open their leaves in daytime and close them at night. It was assumed which this 【S1】______ periodic change was triggered by the alternating sunlight and darkness. Such leaves stick to their daily routine even when keeping in constant darkness. 【S2】______ What is circadian rhythm? Many biological processes follow a 24-hours 【S3】______ schedule. These cycles are called circadian rhythms. These innate rhythms are governed by sophisticated chemical mechanisms can be described as biological 【S4】______ clocks. Such rhythms are important for humans too! We sleep through most of the hours of darkness and are awaken through most of the hours of 【S5】______ daylight. Body temperature increases during the day and decreases during the night. The secretion of various hormones that controls life's processes rises 【S6】______