Protists are a diverse group of microscopic organisms that belong to the kingdom Protista. They can be found in various environments, including freshwater, saltwater, and soil. Protists can be single-celled or multicellular and exhibit a wide range of characteristics. Some, like amoebas, move and feed by changing shape, while others, like algae, perform photosynthesis and produce oxygen. These organisms play essential roles in ecosystems. For example, phytoplankton, a type of algae, forms the base of the marine food web, providing energy for many aquatic animals. Additionally, some protists, such as paramecia, help decompose organic matter, recycling nutrients back into the environment.