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examBoard: Pearson Edexcel
examType: IGCSE
lessonTitle: Respiration and ATP Production
Respiration is one of the most important life processes happening in your body right now. It's how your cells get energy from food and it happens in every living cell all the time. Don't confuse it with breathing (which scientists call ventilation) - respiration happens at the cellular level!
Key Definitions:
All living organisms need energy to:
The food we eat contains chemical energy stored in molecules like glucose. Through respiration, our cells break down these molecules in a controlled way to release energy. This energy is then stored in ATP molecules, which act like rechargeable batteries for our cells.
ATP (adenosine triphosphate) is often called the "energy currency" of cells. Just like you need money to buy things, cells need ATP to power almost everything they do.
ATP consists of an adenosine molecule attached to three phosphate groups. The bonds between these phosphate groups store energy. When a phosphate group is removed, energy is released that the cell can use and ATP becomes ADP (adenosine diphosphate).
ATP → ADP + Pi + Energy
When energy is needed, the bond between the last two phosphate groups is broken. This releases energy for the cell to use and converts ATP to ADP. Later, through respiration, ADP can be converted back to ATP by adding a phosphate group.
Aerobic respiration is the most efficient way to release energy from glucose. It requires oxygen and produces carbon dioxide and water as waste products.
The equation for aerobic respiration:
Glucose + Oxygen → Carbon Dioxide + Water + Energy (ATP)
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + ATP
Aerobic respiration happens in four main stages:
Location: Cytoplasm
Process: Glucose (6C) is split into two pyruvate (3C) molecules.
Energy yield: 2 ATP (net)
Location: Mitochondrial matrix
Process: Pyruvate is converted to acetyl coenzyme A, releasing CO₂.
Energy yield: No direct ATP
Location: Mitochondrial matrix
Process: Acetyl CoA enters a cycle of reactions, releasing CO₂.
Energy yield: 2 ATP per glucose
Location: Inner mitochondrial membrane
Process: Electrons pass along a chain of carriers, pumping H⁺ ions across the membrane. These ions flow back through ATP synthase, generating ATP. Oxygen is the final electron acceptor, combining with H⁺ to form water.
Energy yield: 28 ATP per glucose
From one glucose molecule:
Mitochondria are the powerhouses of the cell where most ATP is produced. Mitochondrial diseases occur when mitochondria don't work properly, often due to genetic mutations. These rare conditions affect about 1 in 5,000 people and can cause muscle weakness, exercise intolerance, heart problems and neurological issues. Since cells can't make enough ATP, the body's most energy-demanding tissues (like muscles and the brain) are most severely affected. There's currently no cure, but research is ongoing to develop treatments.
When oxygen is in short supply, such as during intense exercise, your muscles can switch to anaerobic respiration. This process doesn't require oxygen but produces much less ATP.
Equation:
Glucose → Lactic Acid + Energy (ATP)
During intense exercise, your muscles may not get enough oxygen. They switch to anaerobic respiration, which produces lactic acid. This causes muscle fatigue and pain.
Energy yield: Only 2 ATP per glucose molecule
After exercise, you continue breathing heavily to:
The lactic acid is either converted back to glucose in the liver or broken down completely to carbon dioxide and water.
Understanding respiration is crucial for athletes and sports scientists. Elite athletes train to increase their aerobic capacity (ability to use oxygen) and their anaerobic threshold (the point at which lactic acid starts to build up). Interval training, where athletes alternate between high-intensity exercise and rest periods, helps improve both systems. Athletes also use carbohydrate loading before events to maximize glucose stores, ensuring plenty of fuel for respiration during competition.
Respiration is the process that releases energy from food molecules like glucose. This energy is stored in ATP, which powers all cellular activities. Aerobic respiration uses oxygen and produces 32 ATP per glucose molecule, while anaerobic respiration occurs without oxygen and produces only 2 ATP. Understanding these processes helps explain how our bodies function during different activities and why we feel tired during intense exercise.
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