Give a scenario where a cell may need to perform a form of exocytosis

Exocytosis is the cellular process in which intracellular vesicles in the cytoplasm fuse with the plasma membrane and release or "secrete" their contents into the extracellular space. Exocytosis can be constitutive (occurring all the time) or regulated.

the cell cycle is the final answer! : )

any abiotic or biotic factor in an ecosystem that causes a population's size to slow or decrease is a limiting factor.