---
title: "Anaerobic Respiration"
description: "Explain anaerobic respiration in animals as the incomplete breakdown of glucose to lactic acid when oxygen is in short supply, causing muscle fatigue; contrast this with aerobic respiration in terms o"
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retrieved: 2026-10-19
---

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# Anaerobic Respiration

Explain anaerobic respiration in animals as the incomplete breakdown of glucose to lactic acid when oxygen is in short supply, causing muscle fatigue; contrast this with aerobic respiration in terms of energy yield and products

Subject: Science · Area: Organisms & Life Processes · Ages 12 to 14
Page: https://lightmysky.com/learn/science/anaerobic-respiration-mt_TKZefYXaVS

## Ready when they can

- Writes the word equation for anaerobic respiration in animals
- Explains why lactic acid causes muscle pain and fatigue
- Compares the energy released by aerobic and anaerobic respiration
- Explains oxygen debt and recovery after vigorous exercise

## Lesson: Anaerobic Respiration: Energy Without Oxygen

When you exercise hard, like sprinting, your muscles need energy fast. Usually your body uses oxygen to release that energy. But when oxygen runs short, muscle cells switch to a backup process called anaerobic respiration:

glucose → lactic acid (+ a small amount of energy)

This reaction needs no oxygen, which is why it's called anaerobic.

**Example.** Mia sprints as fast as she can for 100 metres. Halfway through, her blood can't deliver oxygen to her leg muscles fast enough, so those muscles start respiring anaerobically. This keeps her legs supplied with some energy, but far less than aerobic respiration would give.

*(drawing: Aerobic respiration releases far more energy than anaerobic respiration, because it breaks glucose down completely using oxygen.)*

The anaerobic reaction only breaks glucose down part way, turning it into a substance called lactic acid. Lactic acid builds up in the working muscle, and it's the reason your muscles start to ache, burn and feel tired during hard exercise.

**Tip.** After you stop exercising, you keep breathing hard for a while. That extra oxygen is used to break down the lactic acid left in your muscles. This is called repaying your oxygen debt, and it's why you keep panting even after you've stopped running.

**Recap.** When oxygen runs short, muscles make quick energy by turning glucose into lactic acid, and afterward your body uses extra oxygen to clear it away.

## Practice

8 questions on this page, each with its working shown.

## Needs first

- [Aerobic Respiration](https://lightmysky.com/learn/science/aerobic-respiration-mt_mquPi2IP-J)

## Opens up

- [Respiration: Energy Yield, Oxygen Debt and Fermentation](https://lightmysky.com/learn/science/respiration-energy-yield-oxygen-debt-and-fermentation-mt_mvnCjThdTH)