Photoperiodism is __________.

• A. the ability to perceive shortwave ultraviolet light
• B. an attraction to light
• C. found only in plants
• D. an aversion to light
• E. a physiological response of an organism to alternating light and dark cycles

Answer: (E)

Verified step by step guidance

1. Understand the term 'photoperiodism': It refers to the physiological reaction of organisms to the length of day or night. This is a critical concept in biology, especially in understanding how plants and some animals regulate their activities based on light cycles.
2. Identify the key components of photoperiodism: It involves the detection of light and dark periods, which can influence various biological processes such as flowering in plants, breeding in animals, and other seasonal behaviors.
3. Differentiate photoperiodism from other light-related terms: Unlike phototropism (growth towards light) or photophobia (aversion to light), photoperiodism specifically deals with the timing of biological activities in response to the length of day and night.
4. Recognize the organisms affected by photoperiodism: While it is most commonly associated with plants, many animals also exhibit photoperiodic responses, such as changes in reproductive cycles or migration patterns.
5. Apply the concept to the given options: The correct answer is 'a physiological response of an organism to alternating light and dark cycles,' as it accurately describes the essence of photoperiodism.