Einzeller, or "unicellular organisms," are living entities composed of a single cell. They can be found in various environments, including soil, water, and even inside other organisms. Examples of Einzeller include bacteria, protozoa, and yeasts. These organisms perform all necessary life functions within their single cell, such as reproduction, metabolism, and response to stimuli. Despite their simplicity, Einzeller play crucial roles in ecosystems. They contribute to nutrient cycling, serve as food for larger organisms, and can even be involved in processes like fermentation. Understanding Einzeller is essential for fields like microbiology and ecology, as they impact both health and environmental systems.