AQA · GCSE · Biology

    Course version: 8461 · Version from Sept 2018

    The carbon cycle returns carbon from organisms to the atmosphere as carbon…

    Full specification wording

    How materials are cycled: The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis.

    Carbon is recycled between living organisms, the atmosphere and the ground.

    Checked against the AQA 8461 specification (opens in a new tab) on .

    • Point 3 of 5
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    Carbon is recycled between living organisms, the atmosphere and the ground. Plants take in carbon dioxide from the air for photosynthesis, incorporating carbon into glucose and then into carbohydrates, proteins and lipids. Animals gain carbon by eating plants or other animals. Respiration in plants, animals and decomposers releases carbon dioxide back to the atmosphere. When organisms die, detritus feeders and microorganisms break down the remains; decomposition and respiration return carbon dioxide to the air. Burning fossil fuels also adds carbon dioxide, though this is not part of the biological return from organisms. The key idea is that the same carbon atoms are reused, so carbon dioxide removed by photosynthesis is balanced by carbon dioxide released by respiration and decay.

    What earns the marks

    • Plants absorb carbon dioxide from the atmosphere and use it in photosynthesis to make glucose and other carbon compounds.
    • Carbon passes along food chains when animals eat plants or other animals, so carbon is transferred between organisms.
    • Respiration in plants, animals and microorganisms releases carbon dioxide back to the atmosphere.
    • Decomposers break down dead organisms and waste, and their respiration returns carbon dioxide to the atmosphere.
    • Combustion of fossil fuels releases carbon dioxide, but this is an additional human source rather than a return from living organisms.

    Common mistakes and how to put them right

    • Saying plants take in oxygen for photosynthesis.

      Put it right: Plants take in carbon dioxide for photosynthesis and release oxygen.

    • Claiming carbon is returned to the atmosphere only by animals.

      Put it right: Plants and microorganisms also respire and release carbon dioxide.

    • Confusing decomposition with photosynthesis.

      Put it right: Decomposition breaks down dead material and releases carbon dioxide, whereas photosynthesis removes carbon dioxide.

    Exam tips

    • Use the phrase 'carbon dioxide from the atmosphere' when describing the input to photosynthesis, and 'returned to the atmosphere' when describing respiration and decay.
    • Link each stage to a named process such as photosynthesis, feeding, respiration or decomposition rather than writing a vague sequence.
    • If asked to explain balance, state that carbon dioxide removed by photosynthesis is replaced by carbon dioxide released by respiration and decomposition.

    Try the lesson

    The start of the How materials are cycled: The carbon cycle returns carbon from organisms to the atmosphere as carbon dioxide to be used by plants in photosynthesis. lesson, made from checked teaching notes for this specification point.

    Have a go first

    In the carbon cycle, which gas is released into the atmosphere when living organisms respire?

    Listen

    Carbon is recycled between living organisms, the atmosphere and the ground. Plants take in carbon dioxide from the air for photosynthesis, incorporating carbon into glucose and then into carbohydrates, proteins and lipids. Animals gain carbon by eating plants or other animals. Respiration in plants, animals and decomposers releases carbon dioxide back to the atmosphere. When organisms die, detritus feeders and microorganisms break down the remains; decomposition and respiration return carbon dioxide to the air. Burning fossil fuels also adds carbon dioxide, though this is not part of the biological return from organisms. The key idea is that the same carbon atoms are reused, so carbon dioxide removed by photosynthesis is balanced by carbon dioxide released by respiration and decay. A strong answer earns marks for these points. Plants absorb carbon dioxide from the atmosphere and use it in photosynthesis to make glucose and other carbon compounds. Carbon passes along food chains when animals eat plants or other animals, so carbon is transferred between organisms. Respiration in plants, animals and microorganisms releases carbon dioxide back to the atmosphere. Decomposers break down dead organisms and waste, and their respiration returns carbon dioxide to the atmosphere. A common slip: Saying plants take in oxygen for photosynthesis. Instead, plants take in carbon dioxide for photosynthesis and release oxygen. Exam tip: Use the phrase 'carbon dioxide from the atmosphere' when describing the input to photosynthesis, and 'returned to the atmosphere' when describing respiration and decay.

    See it

    A top-down flowchart. At the top is a node labelled carbon dioxide in the atmosphere, which points down to plants taking in carbon dioxide for photosynthesis. That points to carbon in glucose and other carbon compounds in plants. From there one arrow goes to animals eating plants or other animals, and another arrow goes to respiration in plants. The animals node leads to respiration in animals and also to organisms dying and waste being produced. That leads to decomposers breaking down dead organisms and waste, which leads to respiration of microorganisms. Three arrows point back up to the atmosphere node: from respiration in plants, from respiration in animals, and from respiration of microorganisms.
    This shows how carbon moves from the atmosphere into plants and animals and is returned to the atmosphere as carbon dioxide by respiration and decomposition.

    Key words

    Say what each word means before you turn the card.

    Photosynthesis

    Try answering aloud or in your head before turning the card.

    Respiration

    Try answering aloud or in your head before turning the card.

    Decomposition

    Try answering aloud or in your head before turning the card.

    Combustion of fossil fuels

    Try answering aloud or in your head before turning the card.

    See every definition
    Photosynthesis
    The process in which plants take in carbon dioxide from the atmosphere and use it to make glucose and other carbon compounds.
    Respiration
    A process in plants, animals and microorganisms that releases carbon dioxide back to the atmosphere.
    Decomposition
    The breaking down of dead organisms and waste by decomposers, whose respiration returns carbon dioxide to the atmosphere.
    Combustion of fossil fuels
    Burning fossil fuels, which releases carbon dioxide as an additional human source rather than a return from living organisms.

    Label the diagram

    Some boxes have lost their names. Pick the right name for each number.

    The diagram again, with 3 boxes numbered instead of named. A top-down flowchart. At the top is a node labelled carbon dioxide in the atmosphere, which points down to plants taking in carbon dioxide for photosynthesis. That points to carbon in glucose and other carbon compounds in plants. From there one arrow goes to animals eating plants or other animals, and another arrow goes to respiration in plants. The animals node leads to respiration in animals and also to organisms dying and waste being produced. That leads to decomposers breaking down dead organisms and waste, which leads to respiration of microorganisms. Three arrows point back up to the atmosphere node: from respiration in plants, from respiration in animals, and from respiration of microorganisms.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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