Single celled organisms are able to maintain homeostasis, withstanding relatively large alterations in their external environments . This is due to the fact that they posses structures that regulate and carry out life functions. They perform all the functions that are necessary for an organism to exist.
The ability to obtain all the substances that are essential for their existence eliminates the need for dependence on other cells. These single-celled organisms are thus able to maintain a relative state of equilibrium within their internal environment.
