Tetrahymena is a genus of single-celled organisms known as ciliates, which are found in freshwater environments. These microorganisms are characterized by their hair-like structures called cilia, which they use for movement and feeding. Tetrahymena plays a significant role in aquatic ecosystems by helping to decompose organic matter and serving as a food source for larger organisms. Researchers often study Tetrahymena in laboratory settings due to its simple structure and rapid reproduction. It has been instrumental in various scientific fields, including genetics and cell biology, providing insights into cellular processes and the functioning of eukaryotic cells.