Organelles in the cytoplasm where energy production takes place; contains its own DNA.

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

Answer: (B)

Energy production in cells happens mainly in mitochondria, the powerhouses of the cell. These organelles sit in the cytoplasm and generate most of the cell’s ATP through cellular respiration, with glycolysis occurring in the cytosol and the citric acid cycle plus oxidative phosphorylation taking place inside the mitochondria. A key clue is that mitochondria contain their own circular DNA, separate from the nuclear genome, which reflects their origin through endosymbiosis. The cytoplasm is the fluid part of the cell, not an organelle; the nucleus houses genetic material; and the endoplasmic reticulum is involved in protein and lipid synthesis. Because the energy-producing organelle with its own DNA fits all these features, mitochondria are the correct choice.