What is the theorized process by which early eukaryotic cells formed from simpler prokaryotes?

What is the theorized process by which early eukaryotic cells formed from simpler prokaryotes?

• A. Binary fission
• B. Transduction
• C. Endosymbiosis
• D. Apoptosis

Answer: (C)

Endosymbiosis explains how early eukaryotic cells formed when a larger host cell engulfed smaller prokaryotes and they began living inside as a mutualistic partnership. Over time, these internalized bacteria evolved into organelles like mitochondria, and in plants and algae, chloroplasts. The fit is strong because mitochondria and chloroplasts each carry their own circular DNA and ribosomes, resemble bacteria in structure, and replicate by a division similar to binary fission within the cell. This arrangement provided the host with more efficient energy production and protection, while the engulfed cells gained a stable environment and nutrients, making the partnership advantageous and enduring. The other processes don’t describe this origin: a simple division of bacteria (binary fission) is just how bacteria reproduce, not how eukaryotes emerged; transferring genes via viruses (transduction) is a different mechanism of genetic exchange; programmed cell death (apoptosis) is a later cellular process, not a way to form the first eukaryotic cells.

Endosymbiosis explains how early eukaryotic cells formed when a larger host cell engulfed smaller prokaryotes and they began living inside as a mutualistic partnership. Over time, these internalized bacteria evolved into organelles like mitochondria, and in plants and algae, chloroplasts. The fit is strong because mitochondria and chloroplasts each carry their own circular DNA and ribosomes, resemble bacteria in structure, and replicate by a division similar to binary fission within the cell. This arrangement provided the host with more efficient energy production and protection, while the engulfed cells gained a stable environment and nutrients, making the partnership advantageous and enduring.

The other processes don’t describe this origin: a simple division of bacteria (binary fission) is just how bacteria reproduce, not how eukaryotes emerged; transferring genes via viruses (transduction) is a different mechanism of genetic exchange; programmed cell death (apoptosis) is a later cellular process, not a way to form the first eukaryotic cells.