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Chemistry of the Atmosphere

How oxygen increased and carbon dioxide decreased

  • 3 things to know
  • Paper 2

Overview

Photosynthesis by algae and plants as the source of atmospheric oxygen, its word and balanced equations, when oxygen first appeared and why animals evolved later, how carbon dioxide fell through photosynthesis and the formation of sedimentary rocks and fossil fuels, and how limestone, coal, crude oil and natural gas formed.

What you need to know

Answer each one before you reveal it.

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Process

Which process produced the oxygen that is now in the atmosphere?

Key term

State the word equation for photosynthesis.

Key term

State the balanced symbol equation for photosynthesis.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which process produced the oxygen that is now in the atmosphere?

    Model answer

    Photosynthesis by algae and plants.

  2. 2

    State the word equation for photosynthesis.

    Model answer

    Carbon dioxide + water → glucose + oxygen.

  3. 3

    State the balanced symbol equation for photosynthesis.

    Model answer

    6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂.

  4. 4

    Which two substances are used up in photosynthesis?

    Model answer

    Carbon dioxide and water.

  5. 5

    Which organisms first produced oxygen, and roughly when?

    Model answer

    Algae, about 2.7 billion years ago.

  6. 6

    What happened to oxygen in the atmosphere soon after algae began to photosynthesise?

    Model answer

    Oxygen began to appear in the atmosphere and its percentage started to rise.

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