According to the endosymbiotic theory, which of the following organelles were originally free-living prokaryotes that were engulfed by larger eukaryotic cells?

• A. Golgi apparatus and endoplasmic reticulum
• B. Mitochondria and chloroplasts
• C. Ribosomes and lysosomes
• D. Nucleus and peroxisomes

Answer: (B)

Verified step by step guidance

1. Understand the endosymbiotic theory: This theory suggests that certain organelles in eukaryotic cells originated as free-living prokaryotic cells that were engulfed by ancestral eukaryotic cells. These prokaryotes formed a symbiotic relationship with the host cell, eventually evolving into organelles.
2. Identify the key features of mitochondria and chloroplasts: Both organelles have their own DNA, which is circular like prokaryotic DNA, and they have double membranes. They also reproduce independently of the host cell through a process similar to binary fission, which is characteristic of prokaryotes.
3. Compare the other options: The Golgi apparatus, endoplasmic reticulum, ribosomes, lysosomes, nucleus, and peroxisomes do not have their own DNA or exhibit characteristics of prokaryotic cells. These organelles are thought to have evolved differently and are not associated with the endosymbiotic theory.
4. Focus on the correct answer: Mitochondria and chloroplasts are the only organelles in the list that fit the criteria of the endosymbiotic theory, as they were originally free-living prokaryotes.
5. Conclude by reinforcing the concept: The endosymbiotic theory is supported by evidence such as the presence of prokaryotic-like DNA, double membranes, and independent reproduction in mitochondria and chloroplasts, making them the correct answer.