Respiration · Grade 7
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
- Aerobic respiration (with oxygen): glucose + oxygen → carbon dioxide + water. It releases a lot of energy and happens in the mitochondria.
- 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
Example 1
In a respirometer, some germinating peas take in 3.6 cm³ of oxygen in 12 minutes. What is their rate of respiration?
Answer: 0.3 cm³ of oxygen per minute