Which of the following statements is true regarding the endosymbiotic theory?

• A. Mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells.
• B. The endosymbiotic theory suggests that eukaryotic cells evolved from a symbiotic relationship between two eukaryotic cells.
• C. According to the endosymbiotic theory, mitochondria and chloroplasts are the only organelles that originated from endosymbiosis.
• D. The endosymbiotic theory explains the origin of the eukaryotic nucleus.

Answer: (A)

Verified step by step guidance

1. Begin by understanding the endosymbiotic theory, which proposes that certain organelles within eukaryotic cells, specifically mitochondria and chloroplasts, originated from free-living prokaryotes. These prokaryotes were engulfed by ancestral eukaryotic cells, leading to a symbiotic relationship.
2. Examine the statement that mitochondria and chloroplasts originated from free-living prokaryotes. This aligns with the core idea of the endosymbiotic theory, which is widely supported by scientific evidence such as the presence of their own DNA and double membranes.
3. Consider the statement that the endosymbiotic theory suggests eukaryotic cells evolved from a symbiotic relationship between two eukaryotic cells. This is incorrect because the theory specifically involves prokaryotic cells being engulfed by eukaryotic ancestors, not a relationship between two eukaryotic cells.
4. Evaluate the claim that mitochondria and chloroplasts are the only organelles that originated from endosymbiosis. While these are the most well-known examples, some evidence suggests other organelles may have similar origins, but mitochondria and chloroplasts are the primary focus of the theory.
5. Analyze the statement that the endosymbiotic theory explains the origin of the eukaryotic nucleus. This is not accurate, as the theory primarily addresses the origin of mitochondria and chloroplasts, not the nucleus.