Question

The endosymbiosis hypothesis explaining the evolution of eukaryotic cells is supported by a. DNA-sequencing analysis comparing bacterial genomes, mitochondrial genomes, and eukaryotic nuclear genomes. b. naturally occurring examples of endosymbiotic relationships between bacterial cells and eukaryotic cells. c. the presence of DNA in mitochondria and chloroplasts. d. all of the above. e. a and b only.

Short answer

The correct answer is d. All of the given options (a, b and c) provide support to the endosymbiosis hypothesis explaining the evolution of eukaryotic cells.

Step-by-step solution

Understanding the Endosymbiotic Theory

The endosymbiotic theory is a well-accepted scientific theory which postulates that mitochondria and chloroplasts, the organelles in eukaryotic cells, were once independent prokaryotic organisms that were engulfed by a host organism, leading to a mutually beneficial relationship. This theory has been corroborated through multiple lines of supporting evidence.

Analyzing Statement a

Statement a refers to DNA-sequencing analysis comparing bacterial genomes, mitochondrial genomes, and eukaryotic nuclear genomes. Considering our understanding of the endosymbiotic theory, this statement appears supportive as such analysis results show similarities between the genomes of bacteria and these organelles (mitochondria and chloroplasts), indicating a common ancestry. Hence, statement a supports the endosymbiotic theory.

Analyzing Statement b

Statement b talks about naturally occurring examples of endosymbiotic relationships between bacterial cells and eukaryotic cells. These relationships give us insight into how endosymbiosis could have occurred and evolved. Therefore, statement b also supports the endosymbiotic theory.

Analyzing Statement c

Statement c refers to the presence of DNA in mitochondria and chloroplasts. This fact also supports the endosymbiotic theory as it suggests that these organelles were once independent organisms, similar to bacteria, that had their own genetic material.

Conclusion

Having analyzed all the statements, it is clear that all of them a, b and c, provide support for the endosymbiotic theory, indicating the correct answer is option d - 'all of the above'.

Key concepts

Eukaryotic Cell Evolution

The eukaryotic cell represents a monumental leap in the complexity of life forms on Earth. To understand this transition, the endosymbiotic theory offers a popular explanation for how eukaryotic cells might have evolved from prokaryotic ancestors.

Historically, life began with simple, single-celled organisms without a nucleus or other internal structures, known as prokaryotes. Over time, some of these primitive cells engulfed other, smaller prokaryotes. This theory posits that a symbiotic relationship formed from this event: the larger cell provided protection and nutrients, while the smaller cells, which eventually became organelles such as mitochondria and chloroplasts, supplied additional energy or other advantages.

This evolutionary step was critical, allowing for the great variety of life forms we see today, as it gave rise to the internal compartmentalization that characterizes eukaryotes - cells with a true nucleus and specialized organelles.

Mitochondrial DNA

Mitochondria are known as the powerhouses of the cell, and a crucial aspect of the endosymbiotic theory is the presence of their own DNA, known as mitochondrial DNA (mtDNA).

mtDNA is distinct from the cell's nuclear DNA, hinting at mitochondria's prokaryotic ancestors. The mtDNA is usually circular, resembling the DNA of bacteria, and contains genes crucial for the mitochondria's energy-producing processes. Unlike the majority of our genes, we inherit mtDNA exclusively from our mothers, a characteristic that has proven invaluable in tracing maternal lineages and evolutionary history.

Chloroplast DNA

Chloroplasts, essential for photosynthesis in plants and algae, also contain their own DNA, known as chloroplast DNA (cpDNA).

Like mitochondrial DNA, cpDNA supports the idea that chloroplasts originated from free-living ancestors. This DNA is also circular and has a similar size range to bacterial genomes. The genes found within cpDNA are used in the process of photosynthesis and for the production of some amino acids and fatty acids. The discovery of cpDNA bolstered the endosymbiotic theory by showing that two different organelles had similar independent genetic markers.

DNA-Sequencing Analysis

DNA-sequencing analysis plays a pivotal role in verifying the endosymbiotic theory. By comparing the genomes of mitochondria and chloroplasts with those of bacteria and eukaryotic nuclear genomes, scientists have unearthed striking similarities.

Through advanced sequencing methods, researchers found that certain genes in mitochondrial and chloroplast DNA are more similar to bacterial genes than to the nuclear DNA of the eukaryotic cells in which they reside. This evidence strongly supports the idea that these organelles are descended from bacteria that entered into a symbiotic relationship with early eukaryotes. DNA-sequencing analysis continues to be a powerful tool in studying evolutionary relationships, revealing the deep interconnectedness of life.