Final answer:
Symbiosis played a key role in the origin of eukaryotic organelles through a process called endosymbiosis, where a larger host cell engulfed smaller prokaryotic cells that eventually evolved into mitochondria and chloroplasts. These relationships are supported by genetic and structural evidence and are essential to the evolution of complex eukaryotic cells.
Step-by-step explanation:
The role of symbiosis in the origin of some eukaryotic organelles is fundamental to understanding cellular evolution. This symbiotic relationship is known as endosymbiosis, a process wherein a larger host cell engulfed a smaller prokaryotic cell but did not digest it. Instead, the smaller cell survived inside the host and provided it with additional capabilities. Over time, the endosymbiotic cell became a permanent resident of the host cell, evolving into organelles such as mitochondria and chloroplasts.
Mitochondria, known for aerobic respiration and ATP production, likely evolved from aerobic bacteria. Similarly, chloroplasts, known for photosynthesis in plant cells, probably evolved from engulfed cyanobacteria. The evidence for these events comes from the fact that both mitochondria and chloroplasts contain their own DNA, which is similar to bacterial DNA in sequence and chromosome structure. Their ribosomes also resemble those of bacteria more than those of their eukaryotic host cells. This symbiotic relationship allows for a mutual exchange of resources, making it a cornerstone in the advancement of complex cellular life.
The endosymbiotic theory, widely accepted due to the substantial evidence including DNA sequencing and structural similarities with bacteria, explains this evolutionary process. Originally proposed by Lynn Margulis in the 1960s, the theory has revolutionized our understanding of how eukaryotic cells—and by extension, the vast diversity of life forms they comprise—have come into existence.