The primary role of photosynthetic organisms, such as plants, algae, and some bacteria, in ecosystems is to produce oxygen and organic matter through the process of photosynthesis. By converting solar energy into chemical energy, they create a foundation for energy flow in food chains. These organisms absorb sunlight and carbon dioxide, using them to synthesize glucose, which serves as food for themselves and other organisms. Photosynthetic organisms also help regulate atmospheric gases and contribute to the Earth's carbon cycle, making them vital for ecosystem health.