What is exocytosis?

Exocytosis is specifically defined as a process through which cells expel materials. In this mechanism, the contents of a cell vacuole are released to the exterior of the cell when the vacuole membrane fuses with the cell membrane. This fusion allows the substances contained within the vacuole to be discharged outside the cell, which is a crucial function in many cellular processes, including neurotransmitter release, hormonal secretion, and the removal of waste products.

By contrast, the other options describe different biological processes. Engulfing substances into the cell characterizes endocytosis, which serves to intake materials rather than extrude them. The movement of water across a semi-permeable membrane refers to osmosis, a fundamental process of fluid balance. Lastly, the conversion of light energy into chemical energy in chloroplasts relates to photosynthesis, a vital process for energy transformation in plants rather than the transport mechanisms across cell membranes. Understanding these distinctions helps clarify the specific role and definition of exocytosis within cellular functions.