Photosynthetic microorganisms are tiny organisms that can convert sunlight into energy through a process called photosynthesis. This group includes cyanobacteria, algae, and some bacteria. They play a crucial role in ecosystems by producing oxygen and serving as the foundation of the food web. These microorganisms are found in various environments, including oceans, freshwater, and soil. They utilize chlorophyll and other pigments to capture light energy, which helps them synthesize organic compounds from carbon dioxide and water. This process not only supports their growth but also contributes significantly to the Earth's oxygen supply.