In order to respond to a stimulus in the environment what must an organism do? Explain the role of phytochromes in determining plant responses to the environment. What is the stimulus that phytochromes respond to? How is the structure of a phytochrome related to its function? Explain how jetlag results from disruption of normal feedback loops at work in determining the circadian rhythms of humans. Explain the function of taxis in motile organisms Why do fungi only produce fruiting bodies at specific times? How is fruiting body formation controlled? How is the use of quorum sensing in bacteria advantageous? How are all of the responses discussed in this presentation similar? How do they differ?