Respiration
Section: Biology | Syllabus: Cambridge IGCSE Combined Science (0653)
What is Aerobic Respiration?
Aerobic respiration is the chemical reactions in cells that use oxygen to break down nutrient molecules, releasing energy.
Aerobic respiration occurs in the mitochondria of cells. It requires a constant supply of oxygen and glucose, and produces carbon dioxide and water as waste products.
Common Mistakes
- ❌ Confusing respiration with breathing
- ✓ breathing (ventilation) is the physical movement of air in and out of the lungs. Respiration is the chemical process inside cells that releases energy from glucose. The two are linked - breathing supplies the oxygen that aerobic respiration needs - but they are not the same process
Word Equation
glucose + oxygen → carbon dioxide + water
This equation summarises the overall reaction - in reality, aerobic respiration involves many enzyme-controlled steps.
Balanced Chemical Equation (Supplement)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O
- One molecule of glucose reacts with six molecules of oxygen
- This produces six molecules of carbon dioxide and six molecules of water
- Aerobic respiration releases a large amount of energy per glucose molecule
Uses of Energy in Living Organisms
The energy released by respiration is used for:
- Muscle contraction - e.g. movement of limbs, the heartbeat, breathing movements
- Protein synthesis - building proteins from amino acids
- Cell division - for growth, repair and reproduction
- Growth - building new cell components
- The maintenance of a constant body temperature - in mammals and birds, metabolic reactions including respiration generate heat
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