Respiration is a chemical process occurring in all living cells that releases energy from glucose. Gas exchange provides the oxygen and removes the carbon dioxide produced during respiration.
Aerobic: glucose + oxygen → carbon dioxide + water + energy. C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. Occurs in mitochondria. Releases large amount of energy (as ATP). Used for: muscle contraction, protein synthesis, cell division, active transport, maintaining body temperature. Anaerobic: without oxygen. In animals: glucose → lactic acid + energy (less energy released). In yeast: glucose → ethanol + CO₂ (fermentation). Oxygen debt: extra oxygen needed after exercise to break down lactic acid.
Lungs: gas exchange occurs at alveoli. Alveoli adaptations: very large surface area (600 million alveoli), thin walls (one cell thick), moist lining (gases dissolve), rich blood supply (capillary network maintains concentration gradient). O₂ diffuses from alveoli into blood; CO₂ diffuses from blood into alveoli. Concentration gradient maintained by: ventilation (breathing brings fresh air) and blood flow (carries gases away).
Inhalation: intercostal muscles contract (ribs move up and out), diaphragm contracts and flattens → thorax volume increases → pressure decreases → air drawn in. Exhalation: intercostal muscles relax (ribs drop), diaphragm relaxes and domes upward → thorax volume decreases → pressure increases → air pushed out. Effect of exercise: breathing rate and depth increase → more O₂ for aerobic respiration, more CO₂ removed.
No — this is a common misconception. Breathing (ventilation) is the physical process of moving air in and out of the lungs using the diaphragm and intercostal muscles. Respiration is a chemical process that occurs in every living cell (in mitochondria) where glucose is broken down to release energy. Breathing provides the oxygen for respiration and removes the carbon dioxide waste. All living organisms respire, but not all breathe — plants respire but exchange gases through stomata without a breathing mechanism like lungs.
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