Photoperiodism is the physiological reaction of organisms to the length of day or night, primarily influencing seasonal behaviors such as flowering in plants, breeding in animals, and migration patterns. It is a critical adaptation that helps organisms synchronize their life cycles with environmental changes. Different species may respond to varying lengths of light and darkness, leading to classifications such as short-day, long-day, and day-neutral organisms. This response is regulated by the plant hormone phytochrome and other signaling pathways that detect light changes.