The endosymbiotic theory of organelle evolution is a fascinating concept that explains how eukaryotic cells evolved from prokaryotic cells. This theory proposes that certain organelles, like mitochondria and chloroplasts, were once free-living bacteria that were engulfed by larger cells.

The Origins of the Endosymbiotic Theory
The endosymbiotic theory was first proposed in the 1960s by Lynn Margulis, an American biologist. At the time, this theory was considered controversial and faced criticism from other scientists. However, as more evidence has been discovered over the years, this theory has gained widespread acceptance.

What Is a Prokaryotic Cell?
Before diving into the details of the endosymbiotic theory, it’s important to understand what prokaryotic cells are. These are single-celled organisms that lack a nucleus and other membrane-bound organelles. Bacteria are an example of prokaryotic cells.

What Is a Eukaryotic Cell?
On the other hand, eukaryotic cells are more complex and contain a nucleus and various membrane-bound organelles. These include things like mitochondria (which produce energy for the cell), chloroplasts (found in some plant cells and responsible for photosynthesis), and more.

The Endosymbiotic Theory Explained

According to the endosymbiotic theory, eukaryotic cells evolved from prokaryotic cells through a process called endosymbiosis. This involves one cell engulfing another cell without digesting it.

In this case, it’s believed that a larger prokaryotic cell engulfed a smaller bacterium that was capable of producing energy through cellular respiration (this is what mitochondria do). Over time, these two organisms began to work together in a mutually beneficial relationship. The bacterium provided energy to the larger cell, while the larger cell provided protection and nutrients to the bacterium.

Eventually, this symbiotic relationship became permanent, and the bacterium evolved into what we now know as mitochondria. This process is believed to have happened again when a eukaryotic cell engulfed a photosynthetic bacterium (what we now know as chloroplasts).

Evidence Supporting the Endosymbiotic Theory

While the endosymbiotic theory might sound like a far-fetched idea, there is actually quite a bit of evidence to support it. For example:


The endosymbiotic theory of organelle evolution provides an explanation for how eukaryotic cells evolved from prokaryotic cells. While this theory was once considered controversial, it has gained widespread acceptance over time thanks to mounting evidence in its favor.

As we continue to learn more about cellular biology and evolution, it’s likely that our understanding of this theory will continue to evolve as well. But for now, it remains one of the most compelling explanations for how life on Earth has developed over time.