Final answer:
The endosymbiotic theory is supported by evidence such as DNA similarities between eukaryotic chloroplasts and photosynthetic bacteria, the double membrane structure of chloroplasts and mitochondria, and the replication of these organelles through binary fission, which is similar to bacterial replication.
Step-by-step explanation:
The endosymbiotic theory proposes that eukaryotic cells with the ability to undergo photosynthesis originated from a symbiotic relationship between a non-photosynthetic prokaryotic host cell and a photosynthetic prokaryote that became an internal symbiont. This theory is supported by several distinct pieces of evidence:
- DNA similarities: Chloroplasts in eukaryotic cells have their own DNA, which is similar in sequence and structure to the DNA of photosynthetic bacteria. This indicates that chloroplasts are derived from ancestral photosynthetic bacteria.
- Double membranes: Chloroplasts and mitochondria have double membranes. The inner membrane resembles that of the prokaryotic symbionts, and the outer membrane is consistent with the engulfing eukaryotic cell's plasma membrane, suggesting the engulfment and retention of the symbiont by the host cell.
- Binary fission: Both mitochondria and chloroplasts replicate through a process similar to bacterial binary fission, which is distinct from eukaryotic mitosis, implying a prokaryotic origin.
Furthermore, the genetic evidence provided by James Lake and others suggests that eukaryotic cells may have evolved from a gene fusion event between Archaea and Bacteria, as some eukaryotic genes resemble those of Archaea while others resemble those of Bacteria or are unique. Specifically, the phylogenetic analysis showing the relationship between eukaryotic organellar genes and those of their prokaryotic relatives supports this theory.