AQA · GCSE · Chemistry

    Course version: 8462 · Version from Sept 2018

    Algae and plants decreased the percentage of carbon dioxide in the…

    Full specification wording

    How carbon dioxide decreased: Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.

    This statement explains that algae and plants reduced the percentage of carbon dioxide in the atmosphere through the process of photosynthesis.

    Checked against the AQA 8462 specification (opens in a new tab) on .

    • Point 1 of 3
    • 4 key terms

    Study notes

    From the checked teaching notes for this specification point.

    The idea

    This statement explains that algae and plants reduced the percentage of carbon dioxide in the atmosphere through the process of photosynthesis. During photosynthesis, carbon dioxide is taken in from the atmosphere and used to produce glucose, while oxygen is released. Over billions of years, this process significantly decreased the amount of carbon dioxide in the atmosphere. You should be able to explain the link between photosynthesis and the decrease in carbon dioxide, and relate this to the increase in oxygen. For example, as algae and plants photosynthesised, they removed carbon dioxide and added oxygen, leading to the composition of the atmosphere we have today. This is assessed by your ability to describe and explain this process.

    What earns the marks

    • State that algae and plants carry out photosynthesis.
    • Explain that photosynthesis removes carbon dioxide from the atmosphere.
    • Describe how the removal of carbon dioxide by photosynthesis decreased its percentage in the atmosphere.
    • Link the decrease in carbon dioxide to the increase in oxygen produced by photosynthesis.

    Common mistakes and how to put them right

    • Thinking that algae and plants decreased carbon dioxide by respiration.

      Put it right: Respiration releases carbon dioxide; photosynthesis removes it.

    • Confusing the decrease in carbon dioxide with the increase in oxygen, stating that carbon dioxide increased.

      Put it right: Carbon dioxide decreased while oxygen increased.

    • Believing that the decrease in carbon dioxide was immediate.

      Put it right: It occurred gradually over billions of years as photosynthesis by algae and plants continued.

    Exam tips

    • Remember that photosynthesis uses carbon dioxide and produces oxygen, so it decreases carbon dioxide and increases oxygen.
    • Use the equation for photosynthesis to support your explanation of how carbon dioxide is removed.
    • When asked about changes in atmospheric composition, always link them to the processes of photosynthesis and respiration.

    Try the lesson

    The start of the How carbon dioxide decreased: Algae and plants decreased the percentage of carbon dioxide in the atmosphere by photosynthesis. lesson, made from checked teaching notes for this specification point.

    Have a go first

    Which gas is taken in by algae and plants during photosynthesis, lowering its percentage in the atmosphere?

    Listen

    This statement explains that algae and plants reduced the percentage of carbon dioxide in the atmosphere through the process of photosynthesis. During photosynthesis, carbon dioxide is taken in from the atmosphere and used to produce glucose, while oxygen is released. Over billions of years, this process significantly decreased the amount of carbon dioxide in the atmosphere. You should be able to explain the link between photosynthesis and the decrease in carbon dioxide, and relate this to the increase in oxygen. For example, as algae and plants photosynthesised, they removed carbon dioxide and added oxygen, leading to the composition of the atmosphere we have today. This is assessed by your ability to describe and explain this process. A strong answer earns marks for these points. State that algae and plants carry out photosynthesis. Explain that photosynthesis removes carbon dioxide from the atmosphere. Describe how the removal of carbon dioxide by photosynthesis decreased its percentage in the atmosphere. Link the decrease in carbon dioxide to the increase in oxygen produced by photosynthesis. A common slip: Thinking that algae and plants decreased carbon dioxide by respiration. Instead, respiration releases carbon dioxide; photosynthesis removes it. Exam tip: Remember that photosynthesis uses carbon dioxide and produces oxygen, so it decreases carbon dioxide and increases oxygen.

    See it

    A top-down flowchart. The top node reads 'Algae and plants carry out photosynthesis'. An arrow leads down to 'Carbon dioxide taken in from the atmosphere'. From there one arrow leads to 'Glucose produced' and another leads to 'Percentage of carbon dioxide in the atmosphere decreased'. A separate arrow from the top node leads to 'Oxygen released', which then leads to 'Oxygen in the atmosphere increased'. Finally, an arrow from the decreased carbon dioxide node leads to 'Change occurred gradually over billions of years'.
    It shows how photosynthesis by algae and plants removes carbon dioxide from the atmosphere, decreasing its percentage while releasing oxygen, gradually over billions of years.

    Key words

    Say what each word means before you turn the card.

    Photosynthesis

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    Atmospheric carbon dioxide decrease

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    Role of algae and plants

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    Atmospheric evolution

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    See every definition
    Photosynthesis
    A process in which carbon dioxide is taken in from the atmosphere and used to produce glucose, while oxygen is released.
    Atmospheric carbon dioxide decrease
    The reduction in the percentage of carbon dioxide in the atmosphere caused by algae and plants carrying out photosynthesis.
    Role of algae and plants
    These organisms decreased the percentage of carbon dioxide in the atmosphere by photosynthesis.
    Atmospheric evolution
    The change in the composition of the atmosphere over billions of years as photosynthesis removed carbon dioxide and added oxygen.

    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. The top node reads 'Algae and plants carry out photosynthesis'. An arrow leads down to 'Carbon dioxide taken in from the atmosphere'. From there one arrow leads to 'Glucose produced' and another leads to 'Percentage of carbon dioxide in the atmosphere decreased'. A separate arrow from the top node leads to 'Oxygen released', which then leads to 'Oxygen in the atmosphere increased'. Finally, an arrow from the decreased carbon dioxide node leads to 'Change occurred gradually over billions of years'.

    • 1Box 1

    • 2Box 2

    • 3Box 3

    0 of 3 labelled

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