Cellular respiration occurs in the

Step 1: Analyze the question The question asks which cell organelle is the site of cellular respiration, the process that releases energy from food (glucose) for the cell to use.

Step 2: Explain the concept Cellular respiration is the breakdown of glucose to release energy in the form of ATP:

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)

• Glycolysis (the first stage) happens in the cytoplasm.
• The Krebs cycle and the electron transport chain (which release most of the ATP) happen in the mitochondrion.

Because most of the ATP is made in the mitochondria, they are called the "powerhouse of the cell."

Step 3: Check each option

• A. Chloroplast: the site of photosynthesis, not respiration.
• B. Endoplasmic reticulum: transports materials and helps make proteins and lipids.
• C. Food vacuole: stores and digests food, mostly in protozoans like Amoeba.
• D. Mitochondrion: the site of the Krebs cycle and electron transport, where most of the energy is released. ✔
• E. Nucleus: controls the cell's activities and holds the genetic material (DNA).

Step 4: Answer The correct answer is D. mitochondrion.

Exam tip: Remember "Mitochondrion = Most energy (ATP)" and "Chloroplast = Captures sunlight." Photosynthesis builds food in the chloroplast, while respiration releases energy from food in the mitochondrion.