How were organelles formed in early cells?

The formation of organelles in early cells is primarily attributed to the infolding of the cell plasma membrane. This process involves the inward folding of the membrane, which can create compartments within the cell. These compartments then develop into distinct organelles, allowing for specialization and compartmentalization of various cellular processes.

This theory aligns with our understanding of prokaryotic cells, which, while lacking membrane-bound organelles, demonstrate that a simple, adaptable structure can give rise to more complex functionalities over time through the development of these internalized regions. The infolding of the plasma membrane is considered a significant mechanism that allowed primitive cells to evolve toward the more complex eukaryotic cell structure, which is characterized by the presence of multiple organelles.

Other options, like fusion of pre-existing organelles or spontaneous formation in the cytoplasm, do not adequately describe the origins of organelles as they imply different cellular mechanisms that are less supported by current biological evidence. Moreover, while endosymbiotic events contributed to the development of certain organelles, particularly mitochondria and chloroplasts, they are not the primary mechanism by which organelles were initially formed in early cells.