Which statement correctly describes the Endosymbiotic Theory regarding organelles?

Which statement correctly describes the Endosymbiotic Theory regarding organelles?

• A. Mitochondria and chloroplasts originated as free-living prokaryotes.
• B. Nucleus and Golgi apparatus originated as vesicles.
• C. Endoplasmic reticulum and ribosomes originated as vesicles.
• D. Lysosomes and peroxisomes originated from phagocytosis.

Answer: (A)

Endosymbiotic theory describes how some organelles were once independent prokaryotes that entered a host cell and became integrated as essential components. The statement about mitochondria and chloroplasts originated as free-living prokaryotes matches this idea exactly. The strongest support comes from features that resemble bacteria: circular DNA, ribosomes that are more like bacterial 70S ribosomes than eukaryotic 80S ones, replication by binary fission, and double membranes surrounding these organelles. These lines of evidence together explain why these organelles function so somewhat independently inside the cell and why they carry their own genetic material. Other possibilities don’t fit this specific theory. The nucleus and Golgi apparatus arise from membrane dynamics within the cell’s endomembrane system rather than from a bacterial endosymbiosis. Lysosomes and peroxisomes form through vesicle trafficking and growth from existing organelles, not from engulfed free-living organisms.

Endosymbiotic theory describes how some organelles were once independent prokaryotes that entered a host cell and became integrated as essential components. The statement about mitochondria and chloroplasts originated as free-living prokaryotes matches this idea exactly. The strongest support comes from features that resemble bacteria: circular DNA, ribosomes that are more like bacterial 70S ribosomes than eukaryotic 80S ones, replication by binary fission, and double membranes surrounding these organelles. These lines of evidence together explain why these organelles function so somewhat independently inside the cell and why they carry their own genetic material.

Other possibilities don’t fit this specific theory. The nucleus and Golgi apparatus arise from membrane dynamics within the cell’s endomembrane system rather than from a bacterial endosymbiosis. Lysosomes and peroxisomes form through vesicle trafficking and growth from existing organelles, not from engulfed free-living organisms.