4.4.2.1b - Anaerobic respiration in muscles and fermentation
Anaerobic respiration transfers energy without using oxygen. In this lesson, the important AQA idea is that different cells make different products when they respire anaerobically: muscle cells make lactic acid, while plant and yeast cells make ethanol and carbon dioxide. You also need to know why this transfers less energy than aerobic respiration, and why yeast fermentation matters in bread and alcoholic drinks.
Respiration without oxygen
Anaerobic respiration is respiration without oxygen. It still transfers energy from glucose, but it does not break down glucose completely.
Anaerobic respiration
Respiration that transfers energy from glucose without using oxygen.
AQA describes anaerobic respiration as incomplete oxidation of glucose. Oxidation means reaction with oxygen in the aerobic equation, so if oxygen is not available, glucose is not fully oxidised. Because the oxidation of glucose is incomplete, much less energy is transferred than in aerobic respiration.
This is the core comparison habit: anaerobic respiration is useful when oxygen is not available, but it gives a smaller energy transfer from each glucose molecule.
Muscles make lactic acid
Muscle cells can respire anaerobically if they need to transfer energy but there is not enough oxygen reaching them. In muscle cells, the product is lactic acid.
Anaerobic respiration in muscles
glucose -> lactic acid
This word equation is often the shortest route to full marks. It does not include oxygen, carbon dioxide or water. Those belong to aerobic respiration, not anaerobic respiration in muscles.
Lactic acid can build up in muscles when anaerobic respiration is happening. At this point in the course, the essential point is the link: insufficient oxygen means anaerobic respiration in muscle cells, and anaerobic respiration in muscle cells produces lactic acid.
Oxygen debt
This folder's specification boundary includes oxygen debt, so you should know the basic GCSE meaning. If muscles do not receive enough oxygen, anaerobic respiration produces lactic acid and this creates an oxygen debt.
Oxygen debt
The extra oxygen needed after anaerobic respiration in muscles to deal with the accumulated lactic acid and remove it from cells.
Oxygen debt explains why the body still needs extra oxygen after a period of anaerobic respiration. Here, keep the answer tight: lack of oxygen leads to anaerobic respiration in muscles, lactic acid builds up, and extra oxygen is needed afterwards.
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