Endosymbiotic Loss of Prokaryotic Traits in Mitochondria

Steps:

• Endosymbiotic theory states mitochondria originated from engulfed aerobic prokaryotes.
• Prokaryotes typically have cell walls for protection, but mitochondria integrate into host cells without them.
• Mitochondria retain prokaryote-like features such as circular DNA and ribosomes for independent function.
• The cell wall was lost to allow seamless integration and membrane dynamics within the eukaryotic host.

Why A is correct:

• Mitochondria lack a cell wall, a defining prokaryotic structure for rigidity and protection, as confirmed by endosymbiotic theory where engulfed bacteria shed this barrier for symbiosis.

Why the others are wrong:

• B: Mitochondria maintain circular chromosomes, mirroring prokaryotic DNA structure.
• C: Endoplasmic reticulum is a eukaryotic organelle absent in prokaryotes, so not lost from ancestors.
• D: Mitochondria possess 70S ribosomes, similar to prokaryotic ones, for protein synthesis.

Final answer: A