A symbiotic relationship as described in the endosymbiotic theory would have benefited each cell involved by providing mutual advantages that enhanced survival and function. According to the theory, an ancestral host cell (likely anaerobic) engulfed free-living prokaryotic cells such as aerobic bacteria or photosynthetic bacteria. Instead of digesting these internalized cells, the host and the engulfed cells formed a stable, mutually beneficial relationship
. Benefits to the Host Cell:
- The engulfed aerobic bacteria (which became mitochondria) provided the host cell with a more efficient way to produce energy through aerobic respiration, greatly increasing the cell’s energy supply
- In the case of photosynthetic bacteria (which became chloroplasts), the host cell gained the ability to convert sunlight into chemical energy (photosynthesis), which was especially advantageous for early eukaryotes that evolved into plants and algae
Benefits to the Engulfed Cell:
- The internalized bacteria gained a protected and stable environment inside the host cell, shielding them from external threats and providing access to nutrients
- This stable niche allowed the engulfed cells to thrive and reproduce within the host
Over time, this symbiotic relationship became so integrated that the engulfed cells evolved into organelles (mitochondria and chloroplasts) that could no longer live independently. The host cell and organelles exchanged genetic material and functions, resulting in a single, complex eukaryotic cell
. In summary, the symbiotic relationship allowed the host cell to gain new metabolic capabilities (aerobic respiration and photosynthesis), while the engulfed cells received protection and resources, creating a partnership that was more advantageous than either could achieve alone
. This cooperation was a key step in the evolution of complex life.
