What is the primary role of mitochondria?

• A. Site of photosynthesis in plant cells
• B. Site of cellular respiration that supplies energy
• C. Storage of pigments
• D. Protein synthesis

Answer: (B)

The primary role of mitochondria is to supply energy to the cell by producing ATP through cellular respiration. They take the energy from nutrients and, through a sequence of steps in the mitochondrial matrix and inner membrane, convert it into ATP. First, acetyl-CoA enters the TCA cycle to generate electron carriers (NADH and FADH2). These carriers feed electrons into the electron transport chain on the inner membrane, creating a proton gradient that drives ATP synthase to convert ADP and inorganic phosphate into ATP (oxidative phosphorylation).

Glycolysis occurs in the cytosol, and photosynthesis happens in chloroplasts, not mitochondria, so those options don’t fit. Pigment storage is handled by plastids or other structures, not mitochondria. Protein synthesis is mainly carried out by ribosomes; mitochondria make only a small set of proteins themselves. The key idea is that ATP production via cellular respiration is the mitochondrion’s core function.