Final answer:
The term for a smaller cell living inside a larger cell is 'Endosymbiosis.' This mutually beneficial relationship is central to the endosymbiotic theory of eukaryotic cell evolution, explaining the origins of mitochondria and chloroplasts.
Step-by-step explanation:
The term that describes a relationship in which a smaller cell lives inside a larger cell is B) Endosymbiosis. Endosymbiosis is a type of symbiotic relationship where one organism, typically a smaller one, lives inside another. This relationship is mutually beneficial; for example, the larger cell provides a protected environment and nutrients, while the smaller cell offers certain functions like producing energy or organic molecules.
According to the endosymbiotic theory, eukaryotic cells evolved from a symbiotic relationship between prokaryotic cells. This theory suggests that mitochondria and chloroplasts, which are key organelles within eukaryotic cells, originated from bacteria that were engulfed by a larger host cell. Over time, these engulfed bacteria became integrated into the host cell's structure and function, becoming indispensable elements of the cell.