The endosymbiotic theory states that __________.

• A. certain organelles in eukaryotic cells, such as mitochondria and chloroplasts, originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells
• B. all organelles in eukaryotic cells are formed by the folding of the plasma membrane
• C. eukaryotic cells evolved directly from archaea without any symbiotic events
• D. prokaryotic cells contain membrane-bound organelles similar to those in eukaryotes

Answer: (A)

Verified step by step guidance

1. Understand the endosymbiotic theory: This theory explains the origin of certain organelles in eukaryotic cells, specifically mitochondria and chloroplasts, as a result of a symbiotic relationship between ancestral eukaryotic cells and free-living prokaryotes.
2. Identify the key evidence supporting the theory: Mitochondria and chloroplasts have their own DNA, which is circular like that of prokaryotes, and they replicate independently of the cell. They also have double membranes, consistent with the engulfing process.
3. Analyze the provided options: The correct answer should align with the idea that mitochondria and chloroplasts originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells.
4. Eliminate incorrect options: For example, the statement that 'all organelles in eukaryotic cells are formed by the folding of the plasma membrane' does not align with the endosymbiotic theory. Similarly, the idea that 'eukaryotic cells evolved directly from archaea without any symbiotic events' contradicts the theory. Lastly, 'prokaryotic cells contain membrane-bound organelles similar to those in eukaryotes' is incorrect because prokaryotes generally lack membrane-bound organelles.
5. Select the correct answer: The statement 'certain organelles in eukaryotic cells, such as mitochondria and chloroplasts, originated from free-living prokaryotes that were engulfed by ancestral eukaryotic cells' is consistent with the endosymbiotic theory.