Question

Mitochondria and chloroplasts evolved by endosymbiosis. These organelles originated from prokaryotic cells that became residents in a host cell...............Energy-Converting Organelles

Answer 1

The endosymbiotic theory explains the origin of mitochondria and chloroplasts as a result of prokaryotic cells entering a symbiotic relationship within eukaryotic host cells, supported by genetic and structural evidence.

Step-by-step explanation:

Endosymbiotic Theory Explained

The endosymbiotic theory is a well-supported explanation for the evolution of eukaryotic cells. It proposes that mitochondria and chloroplasts originated from free-living prokaryotes that entered a symbiotic relationship with a primitive eukaryotic host. These organelles retained their prokaryote-like DNA, which is evidence of their bacterial origins. Lynn Margulis significantly contributed to this theory, suggesting that mitochondria evolved from an aerobic bacterium and chloroplasts from cyanobacteria.

Evidence for this theory includes similarities between organelles and bacteria in DNA sequence and chromosome structure, the nature of mitochondrial and chloroplast ribosomes, and the process of binary fission. The theory explains how eukaryotic cells acquired additional functionality through these symbiotic relationships, enhancing their energy-conversion capabilities. While mitochondria are related to acquiring energy from oxygen, chloroplasts enable photosynthesis in plants and some algae.

Evidence for Chronology of Endosymbiosis

Evidence suggests that mitochondria were incorporated into ancestral eukaryotic cells before chloroplasts. This is based on the evolutionary timeline and the role of mitochondria in energy production essential for early eukaryotic survival, while chloroplasts, facilitating photosynthesis, would have been an advantageous addition at a later evolutionary stage.

Answer 2

The endosymbiotic theory explains the origin of mitochondria and chloroplasts in eukaryotic cells as a result of prokaryotic cells establishing a symbiotic relationship within a host cell. Supported by structural and genetic evidence, this theory, proposed by Lynn Margulis, is now widely accepted in the scientific community. Mitochondria likely evolved before chloroplasts, marking an evolutionary turning point.

Step-by-step explanation:

The Endosymbiotic Theory

The endosymbiotic theory posits that mitochondria and chloroplasts, key organelles in eukaryotic cells, originated from prokaryotic cells through a process of endosymbiosis. This evolutionary step is considered crucial in the transition from prokaryotic to eukaryotic life forms. The theory asserts that an ancestral eukaryotic cell engulfed an aerobic prokaryote, which then became a permanent resident inside the host cell, giving rise to mitochondria. Similarly, a photosynthetic prokaryote was also engulfed, eventually evolving into chloroplasts.

Scientific evidence, including similarities in DNA and ribosomal structures as well as their process of division through binary fission, supports this theory. A pioneer in this field, Lynn Margulis, provided substantial evidence in favor of endosymbiosis in the 1960s. Modern genetic sequencing has further corroborated the shared ancestry between these organelles and their bacterial counterparts. As a result, mitochondria and chloroplasts contain their own DNA, which is distinct from the nuclear DNA of the eukaryotic host cell, and they have ribosomes that resemble those of bacteria.

The theory also suggests that mitochondria evolved before chloroplasts based on available evidence. Sources such as Margulis' 1981 book Symbiosis in Cell Evolution, and the observable phenomena of bacterial endosymbionts in modern-day eukaryotic cells, such as those in insects and protists, have lent credence to this theory's validity. Endosymbiosis is now a widely accepted explanation for the origin of mitochondria and chloroplasts in eukaryotic cells, marking a significant milestone in the evolution of complex life on Earth.