How does the structure of the cytoplasmic membrane support the endosymbiotic theory as evidence for a common ancestor of all life?

• A. The cytoplasmic membrane is impermeable to ions, which is a characteristic unique to eukaryotic cells.
• B. The cytoplasmic membrane is composed of a lipid bilayer similar to that of mitochondria and chloroplasts, suggesting a shared evolutionary origin.
• C. The cytoplasmic membrane contains DNA sequences identical to those found in prokaryotic cells, indicating a common ancestor.
• D. The cytoplasmic membrane is involved in photosynthesis, a process that originated in eukaryotic cells.

Answer: (B)

Verified step by step guidance

1. Understand the endosymbiotic theory: This theory suggests that certain organelles, like mitochondria and chloroplasts, originated as free-living prokaryotes that were engulfed by ancestral eukaryotic cells.
2. Examine the structure of the cytoplasmic membrane: The cytoplasmic membrane is primarily composed of a lipid bilayer, which is a fundamental feature shared by both prokaryotic and eukaryotic cells.
3. Compare the membrane structures: Note that mitochondria and chloroplasts also have double membranes, similar to the lipid bilayer of the cytoplasmic membrane, supporting the idea of a shared evolutionary origin.
4. Consider the genetic evidence: While the cytoplasmic membrane itself does not contain DNA, mitochondria and chloroplasts have their own DNA, which is similar to prokaryotic DNA, further supporting the endosymbiotic theory.
5. Evaluate the role of the cytoplasmic membrane: Although the cytoplasmic membrane is not directly involved in photosynthesis, the presence of similar structures in chloroplasts, which are involved in photosynthesis, supports the theory of a common ancestor.