1. The physiological response of organisms to the length of day and night, especially the effect of day length on plant flowering and animal behavior.
Usage: biology; also called photoperiodicity

Examples

• Many plants rely on photoperiodism to determine when to flower in spring.
• Photoperiodism controls the breeding cycles of many bird species.
• The farmer studied photoperiodism to optimize crop yields by understanding how day length affects plant growth.
• Migratory birds use photoperiodism as a cue to begin their seasonal journeys.
• Scientists investigate photoperiodism to predict how plants will respond to changing seasons.
• Photoperiodism explains why some plants flower only during long days while others require short days.