The Endosymbiosis Theory of the origin of cell organelles proposes:
a. Organelles originated when the plasma membrane folded in on itself.
b. Organelles originated when a eukaryote engulfed a prokaryote.
c. Organelles originated when a prokaryotic cell were transferred into a eukaryotic cell through a transport channel.
d. No one has come up with any theories yet!
The correct answer and explanation is:
The correct answer is b. Organelles originated when a eukaryote engulfed a prokaryote.
The Endosymbiosis Theory suggests that certain organelles in eukaryotic cells, such as mitochondria and chloroplasts, originated from prokaryotic cells. According to this theory, billions of years ago, a primitive eukaryotic cell engulfed a prokaryotic cell, such as an aerobic bacterium. Instead of being digested, the engulfed prokaryote formed a mutualistic relationship with its host. Over time, the engulfed bacterium became an integral part of the eukaryotic cell, evolving into the mitochondrion or chloroplast we see in modern eukaryotic cells.
One of the major pieces of evidence supporting this theory is the presence of two membranes surrounding mitochondria and chloroplasts, which resemble the outer and inner membranes of a prokaryotic cell. Additionally, these organelles contain their own DNA, which is circular and similar to the DNA found in bacteria. Mitochondria and chloroplasts also replicate independently of the eukaryotic cell cycle, much like prokaryotes do.
Furthermore, the genetic sequences of mitochondria and chloroplasts are closely related to certain prokaryotic species, supporting the idea that they evolved from an ancient symbiotic relationship. Modern-day examples of symbiosis, such as the relationship between corals and algae, provide further insight into how such endosymbiotic relationships could form.
Over time, the engulfed prokaryote lost many of its original functions, relying on the host cell for resources. In return, the host cell gained the benefits of the prokaryote’s specialized functions, such as energy production in the case of mitochondria. Thus, the Endosymbiosis Theory provides a plausible explanation for the origin of key organelles in eukaryotic cells.