In mammals, tissue respiration takes place in the

Step 1: Analyze the question The question asks where tissue respiration happens in mammals. Tissue respiration (also called cellular or internal respiration) is different from breathing and gas exchange.

Step 2: Explain the concept There are two related processes:

• Breathing / external respiration: air moves into the lungs, and gas exchange happens in the alveoli between air and blood.
• Tissue (cellular) respiration: the body's cells use oxygen to break down glucose and release energy (ATP), producing carbon dioxide and water.

Equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)

Tissue respiration happens inside the cells. Glycolysis occurs in the cytoplasm, and the aerobic stages take place in the mitochondria.

Step 3: Check each option

• A. Alveoli: the site of gas exchange between air and blood, not where tissues use oxygen to release energy.
• B. Cells: correct, because this is where oxygen is used to release energy from food.
• C. Lungs: the organs for breathing and gas exchange.
• D. Nose: a passage for air, where air is filtered, warmed and moistened.
• E. Trachea: the windpipe, which carries air to the bronchi.

Step 4: Answer Tissue respiration takes place in the cells, so the answer is B.

Exam tip: "Tissue" or "cellular" respiration always points to cells (mitochondria). If the question says "gaseous exchange" or "external respiration," think alveoli instead.