Which theory explains the origin of mitochondria and plastids in eukaryotic cells?

The endosymbiont theory explains the origin of mitochondria and plastids in eukaryotic cells by proposing that these organelles originated from free-living prokaryotic organisms that entered into a symbiotic relationship with ancestral eukaryotic cells. According to this theory, early eukaryotic cells engulfed certain prokaryotes—specifically aerobic bacteria, which evolved into mitochondria, and photosynthetic cyanobacteria, which evolved into plastids (like chloroplasts).

This theory is supported by several lines of evidence, including the fact that mitochondria and plastids have their own circular DNA, resembling that of prokaryotes, and they replicate independently of the eukaryotic cell cycle. Additionally, these organelles have double membranes, consistent with the engulfing mechanism proposed by the endosymbiont theory, reflecting their prokaryotic origins.

In contrast, cell theory primarily concerns the basic unit of life, which is the cell, and does not address the evolution of specific organelles. Organic evolution theory addresses the broader context of how life evolves over time but lacks specificity regarding the origin of these organelles. Gene theory focuses on the role of genes in heredity and the expression