Which feature describes mitochondria?

• A. It stores the cell's DNA
• B. Double membrane
• C. It is the main site of protein synthesis
• D. It forms the cytoskeleton

Answer: (B)

Mitochondria are defined by having two membranes: an outer membrane and a highly folded inner membrane. This double-membrane arrangement creates compartments that are essential for energy production—the inner membrane’s folds, or cristae, provide a large surface area for the electron transport chain and ATP synthase, while the matrix houses enzymes of the Krebs cycle. While mitochondria do contain some DNA and ribosomes, they are not the cell’s primary DNA storage nor the main site of protein synthesis, and the cytoskeleton is made of actin filaments, intermediate filaments, and microtubules rather than mitochondria. So the feature that best describes mitochondria is their double membrane.