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Understand Anaerobic Respiration

Worksheet Overview

Did you know that Usain Bolt is currently the fastest sprinter in the world? He ran 100 metres in a record 9.58 seconds!


Image of athletes running


In order to do this, Usain Bolt’s muscles need to respire super quick. He needs all that energy to sprint so fast. But his body can’t keep up with these demands - it can’t respire fast enough. This is where anaerobic respiration steps in. 


Image of females exercising



Anaerobic respiration is where glucose breaks down but without oxygen. Energy is released, but not as much as in aerobic respiration. Lactic acid is produced instead of carbon dioxide and water. Lactic acid can cause painful cramps - something we feel in our muscles that stops us from carrying on. To get rid of the lactic acid, the person has to breathe in deeply in order to get a good supply of oxygen. You have to keep breathing hard for a while, after you stop exercising, to get oxygen back into your muscles to convert the painful lactic acid which has built up, into harmless carbon dioxide and water. The amount of oxygen needed to do this is called the oxygen debt.

Anaerobic respiration can be represented by the equation: 


glucose → lactic acid + energy

The reactant in anaerobic respiration is glucose. The product is lactic acid. Energy is also released.

Anaerobic respiration occurs in the cytoplasm of the cell, and not the mitochondria, as in aerobic respiration. 


Plants can also respire anaerobically. However, they don't produce lactic acid. Glucose is broken down into ethanol and carbon dioxide.


Image of plant and animal cell


Uses of anaerobic respiration


Image of alcohol



Anaerobic respiration is useful in bread making and alcohol brewing. Yeast will respire anaerobically, releasing alcohol and carbon dioxide. The carbon dioxide helps bread to rise, creating its fluffy texture. This process is also known as fermentation.


glucose → alcohol + carbon dioxide


Image of bread made with yeast


In the following activity, you will investigate anaerobic respiration.

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