Algae are simple, photosynthetic organisms that can be found in a variety of aquatic environments, including freshwater, saltwater, and even moist terrestrial habitats. They range in size from microscopic phytoplankton to large seaweeds and play a crucial role in ecosystems by producing oxygen and serving as a primary food source for many aquatic organisms. Algae can be classified into different groups, such as green, brown, and red algae, based on their pigments and cellular structure. Additionally, they have applications in various fields, including biotechnology, food, and biofuels.