In these organelles, the cell performs cellular respiration, takes in nutrients, breaks them down, and turns them into energy (ATP).

• A. Mitochondria
• B. Chloroplast
• C. Ribosome
• D. Nucleus

Answer: (A)

The organelle described is where energy from nutrients is turned into ATP, the cell’s usable energy. Mitochondria carry out the key steps of cellular respiration that produce most of the ATP. While some steps start in the cytoplasm, the mitochondria handle the main processes—the citric acid cycle and oxidative phosphorylation—that release energy from nutrients and store it as ATP. Their structure, with a double membrane and folds called cristae, provides lots of surface area for these reactions to occur efficiently. Plants also have mitochondria, but they use chloroplasts to capture light and make sugars, not to produce ATP through respiration. Ribosomes build proteins instead of generating energy, and the nucleus stores genetic material and directs cell activities. So the organelle described is the mitochondrion.