Which organelle consists of rod-shaped structures in the cytoplasm that provide the principal source of energy for the cell and where catabolism occurs?

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

Answer: (A)

Energy production through cellular respiration happens mainly in mitochondria, the rod-shaped organelles scattered in the cytoplasm. These structures are the site of aerobic breakdown of nutrients to generate ATP, the cell’s energy currency. Within mitochondria, the Krebs cycle operates in the matrix to oxidize acetyl-CoA and produce NADH and FADH2, which feed the electron transport chain on the inner membrane. The chain pumps protons to create a gradient that drives ATP synthase, yielding the bulk of cellular ATP. The mitochondria are therefore the principal location of energy production and major catabolic pathways. In contrast, the nucleus stores genetic material, ribosomes handle protein synthesis, and the endoplasmic reticulum is involved in lipid and protein synthesis and transport, not energy generation.