What do living systems have that separates the internal chemicals from the external chemical environment?

Regarding most of the narrator’s story, which word best describes the tone?

Give examples of selective advantage of organism’s body part/organ

The earths core is made up mainly of what 2 substances? 2. like an egg, earth has a core, a layer surrounding the core, and a thin, hard outer layer. which layers of the earth match the layers of an egg?