In your own words, describe the endosymbiotic theory.
The endosymbiotic theory proposes that eukaryotic cells, which are the building blocks of complex organisms like plants, animals, and fungi, evolved through a symbiotic relationship between different prokaryotic cells. It suggests that a long time ago, one type of prokaryotic cell engulfed another, establishing a mutualistic relationship where both cells benefited from each other's presence. The engulfed cell eventually became an organelle within the host cell, providing essential functions such as energy production or nutrient processing. Over time, the two cells became interdependent to the point where they couldn't survive without each other. This theory helps explain the origins of mitochondria and chloroplasts, which are thought to have originated from symbiotic relationships between ancestors of eukaryotic cells and bacteria or photosynthetic organisms.
The endosymbiotic theory is a scientific hypothesis that explains the origin of eukaryotic cells. It proposes that certain organelles, such as mitochondria and chloroplasts, were once free-living bacteria that were engulfed by another larger host cell. Instead of being digested, these bacteria formed a symbiotic relationship with the host cell, eventually evolving into permanent organelles.
According to the theory, around 1.5 billion years ago, a primitive eukaryotic cell engulfed a free-living aerobic bacterium, which is believed to be the ancestor of mitochondria. This aerobic bacterium provided the host cell with energy through aerobic respiration, while the host cell provided a protected environment and nutrients.
Similarly, an ancestral eukaryotic cell is also believed to have engulfed a photosynthetic bacterium capable of capturing sunlight and converting it into chemical energy. This bacterium is thought to have evolved into chloroplasts, which allowed the host cell to perform photosynthesis and produce organic molecules.
Over time, the symbiotic relationship between the host cell and these engulfed bacteria became mutually beneficial, leading to the integration of their genomes. The host cell provided protection, membrane-bound compartments, and nutrients to the organelles, while the organelles produced energy and performed specialized functions.
This theory is supported by various lines of evidence, including the similarities between mitochondria and certain bacteria, such as their ability to reproduce independently through binary fission and their possession of their own DNA. Additionally, the genomes of mitochondria and chloroplasts are more similar to bacterial DNA than to the rest of the host cell's DNA.
In summary, the endosymbiotic theory suggests that eukaryotic cells evolved through a process of symbiosis, where certain bacteria were incorporated into larger host cells, eventually becoming specialized organelles that play vital roles in the functioning of eukaryotic cells.