Question

Which of the following observations would not be considered evidence for the endosymbiosis theory? a. Mitochondria and chloroplasts have genomes that resemble smaller versions of bacterial genomes. b. Mitochondria, chloroplasts, and bacteria all divide by binary fission. c. Mitochondria, chloroplasts, and bacteria all have ribosomes. d. Mitochondria, chloroplasts, and bacteria all have similar sizes and shapes. e. All of the above are considered evidence for the theory.

Short answer

The observation that would not be considered evidence for the endosymbiosis theory is e.

Step-by-step solution

Understanding the Endosymbiosis Theory

The endosymbiosis theory suggests that mitochondria and chloroplasts were once free-living bacteria that were engulfed by other cells. Over time, they evolved into organelles within the larger cell, providing it with energy in exchange for a protected environment.

Evaluating the Observations

Review each of the observations a - d, to check if they align with the endosymbiosis theory.

Comparing Observations with Theory

Through comparison, it can be seen that observations a - d all provide evidence supporting the theory: a. mitochondrial and chloroplast genomes resemble bacteria; b. all three divide by binary fission; c. all have ribosomes; and d. they all have similar sizes and shapes.

Determine the Incorrect Statement

Since all observations a - d support the endosymbiosis theory, the statement that does not align with the theory is e. 'All of the above are considered evidence for the theory' is false as there isn't a statement in the list that contradicts the theory.

Final Answer

Consequently, e is not considered evidence for the endosymbiosis theory, as it is false that there is a statement that contradicts the theory in the list.

Key concepts

Mitochondrial and Chloroplast Genomes

Mitochondria and chloroplasts are fascinating components of eukaryotic cells, largely due to their unique genetic material. Their genomes are distinct from the cell's main DNA found in the nucleus and share remarkable similarities with bacterial genomes. These organelle genomes are small, circular, and lack the complex packaging associated with eukaryotic chromosomes.

This resemblance isn't accidental. It provides compelling evidence for the endosymbiosis theory, which posits that these organelles originated from free-living bacteria. Each organelle's genome encodes for some essential proteins, but many of their genes have been transferred to the host cell’s nuclear DNA over time. This interdependence is a key marker of their symbiotic relationship.

Binary Fission

Binary fission is a simple form of asexual reproduction observed in prokaryotic organisms, like bacteria. This process involves the duplication of the cell's genetic material followed by the division of the cell into two identical daughter cells. What makes this pertinent to the study of organelle evolution is that mitochondria and chloroplasts also divide through a similar process.

This method of replication is quite distinct from the mitosis seen in eukaryotic cell division, reinforcing the idea that these organelles were once independent bacteria. The fact that they still retain this prokaryotic manner of reproduction despite eons of symbiotic living is a strong testament to their bacterial ancestry.

Organelle Evolution

Delving into organelle evolution enables us to understand the transformative journey from autonomy to endosymbiosis. This transition from free-living bacteria to integral cellular components required both mitochondrial and chloroplast precursors to adapt their functions to suit the host cell's environment.

Through this symbiotic relationship, the host cell gained access to ATP production and photosynthesis, while the bacteria benefitted from a protected and resource-rich environment. Over time, genetic mutations and natural selection further integrated these organelles, streamlining their functions and leading to the complex eukaryotic cells we see today.

Evidence Supporting Endosymbiosis

The endosymbiosis theory is supported by a wealth of scientific evidence. Beyond the similarities in genomes and division methods, mitochondria and chloroplasts also have double membranes, which are likely vestiges of the engulfment process. Their ribosomes more closely resemble those found in bacteria, further hinting at a prokaryotic origin.

The presence of DNA in these organelles that is distinct from the cell’s nuclear DNA, the initiation of their own protein synthesis, and the fact that their growth and division are somewhat autonomous within the cell all lend credence to the theory. The combination of genetic, biochemical, and structural evidence form a cohesive narrative explaining how these organelles evolved within eukaryotic cells.