Which of the following best explains the endosymbiotic theory of how eukaryotic cells originated?

• A. Eukaryotic cells evolved directly from viruses that infected prokaryotic cells.
• B. Eukaryotic cells originated from the fusion of two identical prokaryotic cells.
• C. Eukaryotic cells arose when a larger prokaryotic cell engulfed smaller prokaryotes, which then lived symbiotically inside the host cell.
• D. Eukaryotic cells formed from the spontaneous assembly of complex organelles in the cytoplasm of prokaryotes.

Answer: (C)

Verified step by step guidance

1. Step 1: Understand the concept of the endosymbiotic theory. This theory explains the origin of eukaryotic cells as a result of a symbiotic relationship between different prokaryotic cells. Specifically, it suggests that certain organelles, such as mitochondria and chloroplasts, originated from free-living prokaryotes that were engulfed by a larger host cell.
2. Step 2: Analyze the key evidence supporting the endosymbiotic theory. For example, mitochondria and chloroplasts have their own DNA, which is circular like prokaryotic DNA. They also have double membranes and reproduce independently within the cell, similar to prokaryotic cells.
3. Step 3: Evaluate the options provided in the problem. The correct explanation should align with the idea that eukaryotic cells arose from a larger prokaryotic cell engulfing smaller prokaryotes, which then lived symbiotically inside the host cell.
4. Step 4: Eliminate incorrect options. For example, the idea that eukaryotic cells evolved directly from viruses or formed spontaneously from complex organelles does not align with the evidence or principles of the endosymbiotic theory.
5. Step 5: Confirm the correct answer. The explanation that eukaryotic cells arose when a larger prokaryotic cell engulfed smaller prokaryotes, which then lived symbiotically inside the host cell, is consistent with the endosymbiotic theory and supported by scientific evidence.