Here's how the endosymbiotic theory explains the evolution of eukaryotic cells:
1. A large prokaryotic cell engulfed a smaller prokaryotic cell. This smaller cell wasn't digested but instead became a resident within the larger cell.
2. The engulfed prokaryotic cell developed a symbiotic relationship with the host cell. Over time, the engulfed cell evolved into either:
* Mitochondria: The engulfed cell was likely an aerobic bacterium capable of using oxygen to generate energy. This became the mitochondria, the powerhouses of eukaryotic cells.
* Chloroplasts: In plants and algae, the engulfed cell was likely a photosynthetic bacterium capable of producing food from sunlight. This became the chloroplast, the site of photosynthesis.
3. The host cell and the engulfed cell became interdependent. The host cell provided protection and nutrients, while the engulfed cell provided energy or food. This relationship eventually became so essential that the two cells could no longer survive independently.
So, what cell did the endosymbiotic theory create?
The endosymbiotic theory ultimately led to the evolution of eukaryotic cells, which are much more complex than prokaryotic cells. These eukaryotic cells have:
* A nucleus: This organelle houses the cell's DNA and is surrounded by a double membrane.
* Other membrane-bound organelles: Besides mitochondria and chloroplasts, eukaryotic cells also have other organelles like the endoplasmic reticulum, Golgi apparatus, lysosomes, etc., that perform various functions.
* A more complex cytoskeleton: Eukaryotic cells have a network of protein fibers that provide structural support and help with movement.
* Larger size: Eukaryotic cells are generally larger than prokaryotic cells.
In essence, the endosymbiotic theory explains the evolution of a cell type that is fundamentally different from prokaryotic cells, a cell with a sophisticated internal structure and various functions, which paved the way for the development of all multicellular organisms.
