What is commonly referred to as the powerhouse of the cell?

• A. Nucleus
• B. Mitochondria
• C. Ribosome
• D. Endoplasmic reticulum

Answer: (B)

This question tests understanding of where cellular energy is produced. ATP, the cell’s energy currency, is generated primarily in the mitochondria through cellular respiration. In these organelles, nutrients are processed to produce ATP: the citric acid cycle runs in the matrix, and the electron transport chain sits in the inner mitochondrial membrane. As electrons move through the chain, a proton gradient powers ATP synthase to convert ADP into ATP. The folds of the inner membrane, called cristae, increase surface area and efficiency for these reactions. Mitochondria also contain their own circular DNA and ribosomes, reflecting their specialized energy-producing role.

In contrast, the nucleus stores genetic material and directs cellular activities, ribosomes synthesize proteins, and the endoplasmic reticulum handles protein and lipid synthesis and transport. Their functions are essential but not the primary source of ATP, which is why mitochondria are called the powerhouse.