Which organelle is primarily responsible for converting chemical energy into a readily usable form of energy for the cell?

• A. Nucleus
• B. Ribosome
• C. Mitochondrion
• D. Golgi apparatus

Answer: (C)

The main idea is which organelle generates usable energy for the cell. The mitochondrion is the powerhouse: it carries out cellular respiration to convert nutrients, especially glucose, into ATP, the molecule cells use for most activities. In the mitochondrion, the Krebs cycle and the electron transport chain work together to extract energy and drive the synthesis of ATP from ADP and inorganic phosphate. The inner membrane’s folds, called cristae, increase surface area for the electron transport chain, and ATP synthase uses the proton gradient built across that membrane to make ATP. That’s why this organelle is the primary source of readily usable energy. The other organelles have different roles—nucleus stores DNA and governs gene expression, ribosomes synthesize proteins, and the Golgi apparatus processes and ships cellular products—so they aren’t the main sites of energy production.