Respiration · Grade 11

In Grade 11 you learn: anaerobic respiration; fermentation in yeast; exercise and metabolism; glycolysis and the Krebs cycle.

Respiration is the chemical reaction that releases energy from glucose. It happens all the time in every living cell, in plants and animals alike, and the energy runs everything a cell does: moving, growing, keeping warm and making new molecules. It is not the same as breathing.

Key facts

• Symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O. Respiration is exothermic: it releases energy.
• Anaerobic respiration (without oxygen) in muscles: glucose → lactic acid. It releases much less energy.
• In plant cells and yeast, anaerobic respiration is glucose → ethanol + carbon dioxide. In yeast this is called fermentation, used to make bread and alcoholic drinks.
• During exercise, heart rate and breathing rate rise to bring more oxygen and glucose to the muscles and remove carbon dioxide.
• In hard exercise the muscles respire anaerobically and lactic acid builds up. The oxygen needed afterwards to remove it is the oxygen debt.
• Metabolism is the sum of all the reactions in a cell or the body; respiration provides the energy for many of them.

Worked examples

Other years

• Respiration · Grade 8
• Respiration · Grade 9
• Respiration · Grade 10