Respiration and the carbon cycle Cambridge IGCSE Environmental Management revision
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In plain words
The carbon atoms in your body have been in the air, in plants, in other animals, perhaps in a dinosaur. Carbon is never used up. It goes round, and the trouble starts when people take carbon that was locked away for millions of years and put it back in the air all at once.
9 things to know
- Aerobic respiration is the breakdown of glucose in the presence of oxygen to release energy. Carbon dioxide and water are the waste products.
- The word equation is: glucose + oxygen → carbon dioxide + water.
- All living things respire, all the time, plants as well as animals and decomposers.
- Photosynthesis takes carbon dioxide out of the atmosphere, and plants use the carbon to make glucose.
- Feeding passes carbon along the food chain, from plants to animals.
- Respiration returns carbon to the atmosphere as carbon dioxide.
- Decomposition: when organisms die, decomposers break them down, and the decomposers' respiration releases carbon dioxide.
- Formation of fossil fuels: where dead organisms did not decay fully, their carbon was locked underground for millions of years as coal, oil and gas.
- Combustion, the burning of fossil fuels or wood, releases that carbon as carbon dioxide.
Worked example
Describe how a carbon atom in the air could become part of a fox, and then return to the air.
- A plant takes in the carbon dioxide and uses it in photosynthesis to make glucose.
- A rabbit eats the plant, and a fox eats the rabbit. Feeding passes the carbon along.
- The fox respires, and the carbon returns to the air as carbon dioxide.
- If the fox dies first, decomposers break it down and their respiration releases the carbon.
Tips and tricks
- Only one process takes carbon dioxide out of the air: photosynthesis. Respiration, decomposition and combustion all put it back.
- The equation for respiration is the equation for photosynthesis written backwards. Learn one and you have both.
It lands in your notebook with its questions as flashcards.
Respiration and the carbon cycle: 6 questions and answers
These are the quiz’s questions. Do the quiz first, then come back here for the ones that got you.
Which process removes carbon dioxide from the atmosphere?
Plants use it to make glucose.
What are the waste products of aerobic respiration?
Glucose and oxygen are used up.
What is aerobic respiration for?
Every living cell needs the energy.
How does carbon pass from a plant to an animal?
The animal eats the plant.
What is combustion?
Burning fuels releases carbon dioxide.
How do decomposers return carbon to the atmosphere?Stretch
Decomposers are living things, so they respire.
Quiz
6 questions
Tap an answer and you’ll see straight away whether it’s right, and why.
Worksheet
3 questions, 8 marks. Write your answers on paper, then check them.
Respiration and the carbon cycle
Cambridge IGCSE Environmental Management 0680 · 8 marks · papermunch.org
Name ______________________________ Date ______________
Write the word equation for aerobic respiration.[2]
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Glucose + oxygen → carbon dioxide + water.
Name three processes that release carbon dioxide into the atmosphere.[3]
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Respiration, decomposition and combustion.
Explain how burning fossil fuels changes the balance of the carbon cycle.[3]
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Fossil fuels hold carbon that was locked away for millions of years. Combustion releases it as carbon dioxide much faster than it was stored. Photosynthesis cannot remove it as fast, so the concentration in the atmosphere rises.
Answers: Respiration and the carbon cycle
- 1. Glucose + oxygen → carbon dioxide + water.
- 2. Respiration, decomposition and combustion.
- 3. Fossil fuels hold carbon that was locked away for millions of years. Combustion releases it as carbon dioxide much faster than it was stored. Photosynthesis cannot remove it as fast, so the concentration in the atmosphere rises.