Complex sentence: The human body contains a large number of microrganisms, such as bacteria, fungi and archaea, some of these organisms perform tasks that are useful, while the majority have no beneficial or harmful effect.
Split into simpler sentences: The human body contains a large number of microrganisms, such as bacteria, fungi and archaea. Some of these organisms are known to perform tasks that are useful for the human host, while the majority have no beneficial or harmful effect.