According to endosymbiosis, what is the best explanation about how eukaryotic cells evolved?
Bacteria that were capable of photosynthesis engulfed smaller, heterotrophic bacteria.
Cells that did not fully separate during cellular division fused, forming larger organisms.
Chloroplasts and mitochondria were once prokaryotes that began to live within larger cells.
Two or more prokaryotes fused to form larger, multicellular organisms.
The Correct Answer and Explanation is :
The best explanation of how eukaryotic cells evolved according to the endosymbiotic theory is that chloroplasts and mitochondria were once prokaryotes that began to live within larger cells.
Explanation
The endosymbiotic theory, proposed by Lynn Margulis in the 1960s, suggests that eukaryotic cells originated through a symbiotic relationship between different species of prokaryotes. This theory is supported by several lines of evidence.
Firstly, chloroplasts and mitochondria, the organelles responsible for photosynthesis and energy production, respectively, share striking similarities with prokaryotic cells. Both organelles have their own circular DNA, similar to bacterial DNA, and possess double membranes, which indicate a history of engulfment. The presence of ribosomes in these organelles, resembling those of bacteria, further supports this notion. These organelles replicate independently of the cell cycle through a process resembling binary fission, which is characteristic of prokaryotes.
Secondly, genetic studies have shown that the DNA of mitochondria is closely related to that of alpha-proteobacteria, and the DNA of chloroplasts is closely related to cyanobacteria. This genetic evidence indicates that these organelles likely originated from specific prokaryotic ancestors that were engulfed by an ancestral eukaryotic cell. Rather than being digested, these engulfed bacteria established a symbiotic relationship with their host, providing it with additional advantages, such as increased energy production from mitochondria and enhanced photosynthetic capabilities from chloroplasts.
Over time, the engulfed prokaryotes and their host cells became mutually dependent, leading to the evolution of modern eukaryotic cells. This process explains the complexity and compartmentalization of eukaryotic cells, distinguishing them from their prokaryotic counterparts. The endosymbiotic theory fundamentally reshapes our understanding of cellular evolution, illustrating how cooperation between different life forms can lead to the emergence of new, more complex organisms.