Which organelle generates most of the cell's ATP and is inherited maternally?

• A. Chloroplast
• B. Ribosome
• C. Nucleus
• D. Mitochondria

Answer: (D)

Mitochondria are where most of the cell’s ATP is produced. They carry out cellular respiration: nutrients are broken down, electrons are transferred through the electron transport chain, a proton gradient is generated, and ATP synthase uses that gradient to make ATP. Because a cell contains many mitochondria, and they’re geared for high-energy work, they supply the bulk of cellular energy.

Mitochondria also have their own circular DNA and ribosomes, reflecting their bacterial origins, and they’re inherited mainly from the mother. After fertilization, the sperm’s mitochondria are usually degraded or kept separate, so the offspring’s mitochondrial DNA comes from the egg’s cytoplasm rather than the father’s.

Chloroplasts can generate ATP during photosynthesis, but that’s specific to photosynthetic tissue and not the primary energy source for most cells—ribosomes and the nucleus don’t produce ATP.