Final answer:
Endosymbiosis is a symbiotic process where one cell engulfs another, and over time, the internalized cell becomes an organelle, such as mitochondria or chloroplasts, within the host cell. This theory explains the evolutionary origin of eukaryotic cells and is supported by both genetic similarities and evolutionary studies.
Step-by-step explanation:
What is the Process of Endosymbiosis:The process of endosymbiosis is critical to understanding the evolution of eukaryotic cells. It is a symbiotic relationship where one cell, typically a prokaryotic organism, engulfs another, leading to one living inside the other. Over time, these organisms evolve together, with the internalized cell becoming an organelle, such as a mitochondrion or chloroplast, within the host cell. The endosymbiotic theory, first extensively examined by Lynn Margulis in the 1960s, suggests that eukaryotic cells are a product of such relationships. The hypothesis posits that many eukaryotic genes are closely related to Archaea, while metabolic organelles and energy-harvesting processes can trace their origins back to bacteria.
Recent advancements, like those proposed by James Lake of UCLA/ NASA Astrobiology Institute, indicate that endosymbiotic gene fusion events between an Archaea and a Bacteria species have led to the development of eukaryotic cells. Secondary events have further contributed to organelle diversification within eukaryotes. For instance, in chlorarachniophytes, a secondary endosymbiotic event involved a heterotrophic eukaryote consuming a cyanobacterium, which later became the chloroplast in modern-day chlorarachniophytes. This theory is a cornerstone of evolutionary biology, explaining the possible evolutionary steps that transformed independent prokaryotic cells into complex eukaryotic organelles, eventually leading to the rise of diverse eukaryotic life.