What is the function of the mitochondrion in the cell?

• A. Produces ATP through cellular respiration
• B. Breaks down proteins
• C. Stores calcium
• D. Creates ribosomes

Answer: (A)

ATP production through cellular respiration is the mitochondrion’s main job. The organelle houses the citric acid cycle in its matrix and the electron transport chain in its inner membrane. As fuels like glucose are oxidized, energy-trapping steps generate NADH and FADH2, which feed electrons through the transport chain. The energy from those electrons is used to pump protons across the membrane, creating a gradient that ATP synthase uses to synthesize ATP. The folds of the inner membrane (cristae) increase surface area, making this energy production more efficient. Mitochondria also contain their own DNA and ribosomes, reflecting their semi-autonomous nature, but their central role in most cells is to supply ATP. Calcium storage and release, while mitochondria can influence calcium levels, is mainly handled by other stores like the endoplasmic reticulum. Proteins are broken down by proteasomes and lysosomes, not by mitochondria, and ribosomes are assembled in the nucleus/nucleolus. So the best answer is that the mitochondrion produces ATP through cellular respiration.