Analyze the use of imagery and sound in the following poem by John Keats, "Ode to a Nightingale." Discuss how these stylistic elements contribute to the overall themes of mortality and transcendence. Craft a well-organized essay that includes a clear thesis, supported by textual evidence, demonstrating your understanding of the poem and its deeper meanings.
Note: The provided solution includes an example of a perfect-score answer and explanation. Your response will not be scored.