What term refers to the internal order of living things that differentiates them from their environment?

The term that refers to the internal order of living things that differentiates them from their environment is homeostasis. Homeostasis is the ability of an organism to maintain stable internal conditions, such as temperature, pH, and certain concentrations of ions or nutrients, despite changes in the external environment. This process is crucial for survival as it allows living organisms to function optimally and respond to environmental changes.

In contrast, the other terms do not capture this concept of internal organization. Multicellularity refers to organisms composed of multiple cells that work together, which does not directly address the internal order as it pertains to maintaining stability. An organism is a general term that refers to any individual living entity but doesn't specifically denote the internal regulation aspect. A population refers to a group of individuals of the same species living in a particular area, which focuses more on the external context rather than the internal mechanisms that define life.