Anaerobic respiration
Laura Armstrong & Joe Wolfensohn
Teachers
Contents
Recall Questions
This topic requires prior knowledge of anaerobic respiration from GCSE. You can test your knowledge on this below.
What is anaerobic respiration?
A form of respiration that does not use oxygen to release energy from glucose.
What is the word equation for anaerobic respiration in animals?
Glucose → Lactic acid + (energy)
Why does anaerobic respiration release less energy than aerobic respiration?
Glucose is only partially broken down, so less ATP is produced.
Topic Explainer Video
Check out this @JoeDoesBiology video that explains anaerobic respiration or read the full notes below. Once you've gone through the whole note, try out the practice questions!
Intro to Anaerobic Respiration
Anaerobic respiration occurs when oxygen is not available. It begins with glycolysis, which is common to both aerobic and anaerobic respiration, but is then followed by different pathways depending on the organism.
Glycolysis Recap (First Stage of Anaerobic Respiration)
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Occurs in the cytoplasm.
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Glucose (6C) is phosphorylated using 2 ATP to form glucose bisphosphate.
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This splits to form 2 molecules of triose phosphate.
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Triose phosphate is oxidised to form 2 molecules of pyruvate (3C).
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Produces:
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2 reduced NAD
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4 ATP (2 net gain)
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Does not require oxygen.
Anaerobic Respiration in Animals
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Pyruvate is converted into lactic acid (lactate).
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To do this, the pyruvate is reduced (it gains the hydrogen from NADH)
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This conversion regenerates NAD, allowing glycolysis to continue and ATP production to continue in the absence of oxygen.
Equation
Pyruvate (from glycolysis) + NADH → NAD + Lactic acid
This process is reversible: lactic acid is transported to the liver to be converted back into glucose when oxygen becomes available.
No answer provided.
Anaerobic Respiration in Plants and Yeast (Ethanol Fermentation)
Pyruvate is converted into ethanol and carbon dioxide.
To do this, pyruvate is decarboxylated (removing carbon dioxide) and then reduced (it gains the hydrogen from NADH).
Like in animals, NAD is regenerated to allow glycolysis to continue and ATP production to continue in the absence of oxygen.
Steps:
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Pyruvate (from glycolysis) → Ethanal + CO₂
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Ethanal + NADH → Ethanol + NAD
ATP produced during anaerobic respiration
Only the net gain of 2 ATP from glycolysis during anaerobic respiration.
Key Terms
- Anaerobic respiration: Respiration without oxygen, producing less ATP.
- Lactic acid: Alcohol produced in anaerobic respiration in plants and yeast.
- NAD regeneration: Important to allow glycolysis to continue in anaerobic conditions.
- Glycolysis: First stage of respiration; occurs in the cytoplasm.
No answer provided.
Exam Tip
Always mention that NAD is regenerated during anaerobic respiration — this is a key marking point and shows understanding of how glycolysis continues without oxygen. The NAD can be oxidised (gain hydrogen) again in glycolysis.
No answer provided.
In the presence of oxygen, respiration yields more ATP per molecule of glucose than it does in the absence of oxygen. Explain why. (3 marks)
In aerobic respiration, oxygen acts as the final electron acceptor.
Allowing operation of electron transport chain / oxidative phosphorylation producing ATP.
ATP also produced via Krebs cycle.
Only ATP formed in glycolysis when no oxygen present.
Explain why converting pyruvate to lactate is important in allowing the continued production of ATP in anaerobic respiration in animals. (2 marks)
Regenerates/produces NAD OR oxidises reduced NAD
descriptions of oxidation e.g. loss of hydrogen will be accepted
So glycolysis continues
Practice Question 1
Try to answer the practice question from the TikTok on your own, then watch the video to see how well you did!
Practice Question 2
If you want to try out another one, check this video out and see how you do!