According to the endosymbiotic theory, which of the following is likely the ancestor of the mitochondria?

• A. Aerobic eukaryotes.
• B. Aerobic bacteria.
• C. Anaerobic bacteria.
• D. Cyanobacteria.
• E. Chloroplasts.

Answer: (B)

Verified step by step guidance

1. Understand the endosymbiotic theory: This theory suggests that certain organelles within eukaryotic cells, such as mitochondria and chloroplasts, originated from free-living bacteria that were engulfed by ancestral eukaryotic cells.
2. Identify the function of mitochondria: Mitochondria are known for their role in aerobic respiration, which is the process of producing cellular energy in the presence of oxygen.
3. Consider the characteristics of aerobic bacteria: Aerobic bacteria are capable of using oxygen to generate energy, similar to the function of mitochondria in eukaryotic cells.
4. Evaluate the options: Compare the characteristics of aerobic bacteria with those of mitochondria, noting the similarity in their ability to perform aerobic respiration.
5. Conclude the likely ancestor: Based on the endosymbiotic theory and the functional similarities, aerobic bacteria are considered the most likely ancestors of mitochondria.