Explain the process of photosynthesis and its importance to the ecosystem. Your response should contain at least 5 sentences and at least 150 words. Highlight at least 2 sections in your answer with markdown, i.e. *highlighted section*. In your response, the word "photosynthesis" should appear at least 3 times. Include keywords *sunlight, chlorophyll, carbon dioxide, oxygen, energy*. At the end of your response, please explicitly add a postscript starting with *P.S.*.

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