What theory proposes that eukaryotic cells originated from a symbiotic relationship between multiple prokaryotic ancestors?

• A. Endosymbiotic theory
• B. Abiogenesis
• C. Primordial Soup Theory
• D. Biogenesis

Answer: (A)

Endosymbiotic theory explains how complex eukaryotic cells gained their energy-producing organelles by describing a long-term partnership where one cell engulfed another and the inner cell became mitochondria and, in plants and algae, chloroplasts. The strongest evidence is that these organelles keep their own circular DNA and ribosomes that resemble bacterial ones, and they replicate by binary fission inside the host cell. They also have double membranes, which fits the idea of one cell enveloping another. Genetic analyses show mitochondrial genes resemble proteobacteria and chloroplast genes resemble cyanobacteria, confirming a bacterial origin for these organelles. This concept explains the presence of bacterial traits within eukaryotic cells and how energy production and photosynthesis were incorporated, whereas theories about the origin of life itself don’t specifically account for the acquisition of these organelles.