Green algae are a diverse group of photosynthetic organisms found in various aquatic environments, including freshwater, marine, and even moist terrestrial habitats. They belong to the kingdom Plantae and are characterized by their green color, which comes from chlorophyll. Green algae play a crucial role in ecosystems as primary producers, converting sunlight into energy and providing oxygen and food for other organisms. These organisms can exist as single cells, colonies, or multicellular forms. Some common types of green algae include Chlorella, Spirogyra, and Cladophora. Green algae are also important in scientific research and biotechnology, as they can be used in biofuels, wastewater treatment, and as a food source in aquaculture.