Who this is for: Cambridge IGCSE Biology (0610) students who want anaerobic respiration — lactic acid in animals, fermentation in yeast and oxygen debt — to become reliable marks instead of a vague “without oxygen.”
What query it owns: how to understand and revise anaerobic respiration in Cambridge IGCSE Biology.
Why this is safe: this page owns the anaerobic respiration revision-guide angle, while Tutopiya’s Anaerobic Respiration subtopic page owns the learning resource and the free Anaerobic Respiration quiz owns the practice.

Anaerobic respiration is the chemical process that releases a small amount of energy from glucose when oxygen is insufficient or absent. Cambridge IGCSE Biology (0610) tests whether you can state the products in animals (lactic acid) and yeast (ethanol and carbon dioxide), compare energy release with aerobic respiration, and explain oxygen debt after vigorous exercise. This guide covers the syllabus definitions, the equations examiners expect, and the question types that appear every year.

Key takeaways

• Anaerobic respiration releases a small amount of energy from glucose without using oxygen.
• In animal muscle cells: glucose → lactic acid (+ energy).
• In yeast: glucose → ethanol + carbon dioxide (+ energy) — this is fermentation.
• Oxygen debt is the extra oxygen needed after exercise to break down accumulated lactic acid.
• Exam answers must name the correct products for animals vs yeast — they are not interchangeable.

What is anaerobic respiration in Cambridge IGCSE Biology?

Anaerobic respiration is the chemical process in cells that releases a small amount of energy from glucose when oxygen is not available in sufficient quantity. In animal cells, glucose is partially broken down to lactic acid. In yeast, glucose is broken down to ethanol and carbon dioxide. Anaerobic respiration releases far less energy per glucose molecule than aerobic respiration because glucose is not fully oxidised.

You can read the full explanation, worked examples and notes on Tutopiya’s Anaerobic Respiration subtopic page before you attempt questions.

The core ideas you must master

Idea	What it means	How the exam uses it
No oxygen	Oxygen not used or insufficient	”Define anaerobic respiration.”
Less energy	Small amount vs aerobic	”Compare aerobic and anaerobic respiration.”
Lactic acid	Product in animal muscle cells	”State the product of anaerobic respiration in animals.”
Fermentation	Anaerobic respiration in yeast	”State the products of fermentation.”
Oxygen debt	Extra O₂ after exercise	”Explain what is meant by oxygen debt.”

Anaerobic respiration in animals vs yeast

Feature	Animals (muscle cells)	Yeast
Oxygen	Not used	Not used
Substrate	Glucose	Glucose
Products	Lactic acid	Ethanol + carbon dioxide
Energy released	Small amount	Small amount
Syllabus term	Anaerobic respiration	Fermentation

Anaerobic respiration in past-paper wording: command words that matter

Command word / phrase	What the question wants	Typical anaerobic respiration stem
Define	Precise syllabus definition	”Define anaerobic respiration.”
State	Short factual answer	”State the product of anaerobic respiration in muscle cells.”
Explain	Cause and effect	”Explain why a sprinter breathes heavily after a race.”
Compare	Similarities and differences	”Compare aerobic and anaerobic respiration.”
Describe	What happens, step by step	”Describe what happens to glucose during fermentation in yeast.”

Worked exam-style stems (how to answer the wording)

1. “Define the term anaerobic respiration.” Anaerobic respiration is the chemical process in cells that releases a small amount of energy from glucose without using oxygen. Mark-scheme reward: small amount of energy, without oxygen, glucose.
2. “State the product of anaerobic respiration in animal muscle cells.” Lactic acid. Reward: not carbon dioxide or ethanol — those belong to other contexts.
3. “Explain what is meant by oxygen debt.” During vigorous exercise, lactic acid builds up in muscles. After exercise, extra oxygen is taken in and used to break down the lactic acid to carbon dioxide and water — this extra oxygen is the oxygen debt. Reward: lactic acid breakdown + extra oxygen.
4. “Compare the energy released by aerobic and anaerobic respiration.” Aerobic respiration releases a large amount of energy; anaerobic respiration releases a small amount because glucose is only partially broken down. Reward: quantitative comparison language.

When you can recognise the wording instantly, work the full set on the Respiration topical past paper questions and the Anaerobic Respiration quiz to lock the definitions in.

How anaerobic respiration connects to the rest of the syllabus

Anaerobic respiration sits alongside Aerobic Respiration and the wider Respiration topic. It links to gas exchange (oxygen supply during exercise), enzymes in yeast fermentation practicals, and the uses of energy from respiration. The Cambridge IGCSE Biology resource hub links every Respiration subtopic.

Common mistakes students make

• Stating carbon dioxide as the product of anaerobic respiration in animal muscle cells (that is aerobic respiration or yeast fermentation).
• Confusing fermentation products (ethanol + CO₂) with animal products (lactic acid).
• Saying anaerobic respiration releases the same amount of energy as aerobic respiration.
• Describing breathing faster as anaerobic respiration — breathing is gas exchange; respiration is a chemical process in cells.
• Omitting oxygen debt explanation when asked about recovery after exercise.

When you need more support

If anaerobic respiration questions keep costing marks — especially compare questions with aerobic respiration — work through the Respiration topical past paper questions and the Anaerobic Respiration quiz, then get focused help from a Cambridge IGCSE Biology tutor.

Frequently asked questions

Is anaerobic respiration hard in Cambridge IGCSE Biology? The idea is straightforward, but marks are lost when students mix up animal products (lactic acid) with yeast products (ethanol and carbon dioxide).

What is the difference between anaerobic respiration and fermentation? Fermentation is the name given to anaerobic respiration in yeast, producing ethanol and carbon dioxide. In animals, the syllabus calls it anaerobic respiration and the product is lactic acid.

Why does anaerobic respiration release less energy? Glucose is only partially broken down without oxygen, so less energy is transferred from the glucose molecule compared to complete aerobic breakdown.

How do I revise anaerobic respiration effectively? Read the subtopic notes, memorise both word equations (animals and yeast), compare with aerobic respiration, then take the Anaerobic Respiration quiz.

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