What is cellular respiration, and how do aerobic and anaerobic respiration differ?
Describe cellular respiration as an exothermic reaction that releases energy, compare aerobic and anaerobic respiration, and investigate the rate of respiration in living organisms.
A focused answer to Edexcel GCSE Biology 8.9 to 8.11, covering cellular respiration as an exothermic reaction, the comparison of aerobic and anaerobic respiration in animals and plants, and the respiration-rate core practical.
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What this dot point is asking
Edexcel statements 8.9 to 8.11 want you to describe cellular respiration as an exothermic reaction that releases energy, compare aerobic and anaerobic respiration (in animals and plants/yeast), and carry out the core practical investigating the rate of respiration in living organisms (statement 8.11).
Cellular respiration
The energy released is used for muscle contraction, growth and building larger molecules, keeping the body warm, and active transport. Respiration is the opposite of photosynthesis: it releases the energy that photosynthesis stored in glucose.
Aerobic respiration
Aerobic respiration uses oxygen and releases the most energy:
Because glucose is fully broken down, aerobic respiration transfers a large amount of energy. It is the normal process used by cells when enough oxygen is available.
Anaerobic respiration
Anaerobic respiration is useful when oxygen cannot be supplied fast enough, but it is far less efficient, which is why it is only a short-term backup in muscles.
The core practical: rate of respiration
In the core practical (8.11) you measure how fast living organisms (such as germinating peas or small invertebrates) use oxygen, using a respirometer. The organisms are sealed in a tube with a chemical (such as soda lime) that absorbs the carbon dioxide they release. As they respire, they use up oxygen, and because the carbon dioxide is absorbed, the pressure inside falls, drawing a drop of coloured liquid along a capillary tube towards the organisms. Measuring how far the drop moves in a set time gives the rate of oxygen use, and so the rate of respiration. Keeping the temperature constant in a water bath makes it a fair test.
Try this
Q1. State whether respiration is exothermic or endothermic, and why the cell needs it. [2 marks]
- Cue. Exothermic; it releases energy from glucose for processes such as movement, growth, warmth and active transport.
Q2. Give the products of anaerobic respiration in human muscle and in yeast. [2 marks]
- Cue. In muscle: lactic acid. In yeast: ethanol and carbon dioxide.
Exam-style practice questions
Practice questions written in the style of Pearson Edexcel exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
Edexcel 20194 marksCompare aerobic and anaerobic respiration in human muscle cells.Show worked answer →
A 4-mark compare question rewards linked points about both processes.
Aerobic respiration uses oxygen, fully breaks down glucose to carbon dioxide and water, and releases a large amount of energy. Anaerobic respiration happens without oxygen, breaks glucose down only to lactic acid, and releases much less energy.
Aerobic respiration is the normal process; anaerobic respiration is used during vigorous exercise when oxygen cannot be supplied fast enough, but it causes a build-up of lactic acid and an oxygen debt.
Markers reward the presence or absence of oxygen, the different products (carbon dioxide and water versus lactic acid), and the different amounts of energy released. Saying anaerobic respiration releases more energy is a key error.
Edexcel 20213 marksDescribe how you could investigate the rate of respiration of germinating peas using a simple respirometer.Show worked answer →
A 3-mark describe question rewards the method and what is measured.
Place germinating peas in a sealed tube connected to a capillary tube containing a drop of coloured liquid, with a substance to absorb carbon dioxide (such as soda lime). As the peas respire, they use up oxygen, and because the carbon dioxide is absorbed, the pressure inside falls, so the liquid drop moves towards the peas.
Measure how far the drop moves in a set time to find the rate of oxygen use (the rate of respiration). Keeping temperature constant in a water bath makes it a fair test.
Markers reward using up oxygen, absorbing carbon dioxide, the drop moving, and measuring distance over time. Forgetting to control temperature, or not absorbing the carbon dioxide, loses marks.
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Sources & how we know this
- Pearson Edexcel GCSE (9-1) Biology (1BI0) specification — Pearson (2016)