Year 8 · Science · Breathing and respiration · Lesson 3

Anaerobic respiration

Anaerobic respiration in muscles and in yeast, its word equations, the oxygen debt, fermentation for bread and brewing, and comparing it with aerobic respiration.

23-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

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What your child will learn

Describe anaerobic respiration
Write the word equation for anaerobic respiration in muscles
Write the word equation for fermentation in yeast
Explain the oxygen debt
Compare aerobic and anaerobic respiration

The method

Anaerobic respiration happens without oxygen and releases less energy than aerobic.
In muscles: glucose → lactic acid, causing fatigue and cramp.
In yeast: glucose → ethanol + carbon dioxide (fermentation), used for bread and brewing.
The oxygen debt is the extra oxygen needed after exercise to break down lactic acid.

Key words: anaerobic, lactic acid, oxygen debt, fermentation, yeast, ethanol, carbon dioxide.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

What is the product of anaerobic respiration in human muscles?

Step 1: glucose → lactic acid

Answer: Lactic acid

Question 2

What are the products of anaerobic respiration in yeast?

Step 1: glucose → ethanol + carbon dioxide

Answer: Ethanol and carbon dioxide

Question 3

Which releases more energy: aerobic or anaerobic respiration?

Step 1: Aerobic: glucose is fully broken down
Step 2: Anaerobic: only partly broken down → less energy

Answer: Aerobic respiration