Which organelle provides the principal source of energy for the cell and is rod-shaped?

• A. Nucleus
• B. Ribosomes
• C. Mitochondria
• D. Endoplasmic Reticulum

Answer: (C)

Energy in the cell mostly comes from mitochondria, which are often rod-shaped in many cells. They’re called the powerhouse because they generate ATP, the cell’s main energy currency, through cellular respiration. During this process, the citric acid cycle and oxidative phosphorylation (the electron transport chain) take place in the inner membrane, and the foldings there, called cristae, provide lots of surface area for these reactions to occur efficiently. This energy-producing role is distinct from the nucleus, which stores genetic material and governs activities; ribosomes, which synthesize proteins; and the endoplasmic reticulum, which helps make and fold proteins and lipids but doesn’t supply energy.