Anaerobic respiration Cambridge IGCSE Biology (9–1) revision
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In plain words
In a sprint your muscles need energy faster than your blood can deliver oxygen. They carry on without it for a while, but the fuel isn't fully broken down, so less energy comes out and lactic acid builds up. That's the burn. Yeast does something similar and makes alcohol.
Three things to know
- Anaerobic respiration releases energy from glucose without oxygen. It releases much less energy per glucose molecule than aerobic respiration.
- In muscles: glucose → lactic acid. In yeast: glucose → alcohol (ethanol) + carbon dioxide.
- After hard exercise you keep breathing fast and your heart keeps racing: the extra oxygen is needed to break down the lactic acid. This is the oxygen debt.
Tips and tricks
- Muscles make lactic acid only. No carbon dioxide is produced by anaerobic respiration in animals.
- Yeast is why bread rises (the carbon dioxide) and how beer and wine are made (the alcohol).
It lands in your notebook with its questions as flashcards.
Anaerobic respiration: 5 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
What is produced by anaerobic respiration in muscles?
Lactic acid causes the muscles to ache.
What does yeast produce by anaerobic respiration?
This is fermentation.
Compared with aerobic respiration, how much energy does anaerobic respiration release?
Glucose is only partly broken down.
What is the oxygen debt?
It is "repaid" by fast breathing after exercise.
Which gas makes bread dough rise?
Yeast in the dough gives it off.
Quiz
5 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 7 marks. Write your answers on paper, then check them.
Anaerobic respiration
Cambridge IGCSE Biology (9–1) 0970 · 7 marks · papermunch.org
Name ______________________________ Date ______________
Write the word equation for anaerobic respiration in (a) human muscle and (b) yeast.[2]
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(a) Glucose → lactic acid. (b) Glucose → alcohol (ethanol) + carbon dioxide.
State two differences between aerobic and anaerobic respiration in humans.[2]
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Aerobic uses oxygen and anaerobic does not; aerobic releases much more energy; aerobic produces carbon dioxide and water, anaerobic produces lactic acid.
Explain why an athlete continues to breathe heavily after a race.[3]
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During the race the muscles respired anaerobically and lactic acid built up (an oxygen debt). Extra oxygen is needed to break the lactic acid down, so breathing stays fast and deep.
Answers: Anaerobic respiration
- 1. (a) Glucose → lactic acid. (b) Glucose → alcohol (ethanol) + carbon dioxide.
- 2. Aerobic uses oxygen and anaerobic does not; aerobic releases much more energy; aerobic produces carbon dioxide and water, anaerobic produces lactic acid.
- 3. During the race the muscles respired anaerobically and lactic acid built up (an oxygen debt). Extra oxygen is needed to break the lactic acid down, so breathing stays fast and deep.