Final answer:
The response of an organism to seasonal changes in spring and fall is determined by both critical day length and temperature. Photoperiodism helps them predict conditions, while temperature affects the phenology of lifecycle events.
Step-by-step explanation:
An organism's response to seasonal change in spring and fall is influenced by critical day length and temperature. While photoperiod, or day length, is a significant cue that organisms use to predict upcoming conditions and induce physiological changes, temperature also plays a crucial role.
Photoperiodism is a biological response to the timing and duration of day and night, which controls flowering, setting of winter buds, and vegetative growth in plants. Detection of seasonal changes through changes in day length is crucial for plant and animal survival. However, organisms are also affected by changes in temperature, as it greatly influences the phenology of plants and animals, which includes the timing of various life cycle events like flowering in plants or migration in birds.