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Earth’s Life Support Systems

Water and carbon as the foundations of life on Earth

  • 3 things to know
  • Component 01

Overview

Recall questions on why water and carbon support life: water as a solvent, its thermal properties and role in photosynthesis and transpiration, human water use by sector, wetlands, carbon chemistry and the biosphere, human use of carbon resources, the fast and slow carbon cycles, and carbon dioxide as a resource.

What you need to know

Answer each one before you reveal it.

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Key term

State two properties of water that allow it to moderate temperature.

Key term

Why does a wetland support a high density of animal life?

Key term

How is water used in photosynthesis?

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Why is liquid water described as the universal solvent of life?

    Model answer

    It dissolves nutrients, gases and salts, allowing them to be transported around an organism and to react inside its cells.

  2. 2

    State two properties of water that allow it to moderate temperature.

    Model answer

    Water has a high specific heat capacity, so it warms and cools slowly, and a high latent heat of vaporisation, so evaporation removes large amounts of heat from a surface.

  3. 3

    How is water used in photosynthesis?

    Model answer

    Water supplies the hydrogen that is combined with carbon dioxide to build glucose, and the oxygen released as a by-product comes from the water molecule.

  4. 4

    How does transpiration help a plant obtain mineral nutrients?

    Model answer

    Water lost from the leaves pulls a continuous column of water up the xylem from the roots, and dissolved minerals are carried up with it.

  5. 5

    Name the three sectors of human water use in order of the volume they withdraw.

    Model answer

    Agriculture is much the largest at roughly 70% of withdrawals, then industry at about 20%, then domestic use for drinking, cooking, washing and sanitation at around 10%.

  6. 6

    Why does a wetland support a high density of animal life?

    Model answer

    Permanent shallow water provides drinking water, aquatic plants and invertebrates as food, and sheltered breeding habitat, so many species can be supported in a small area.

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Earth’s Life Support Systems

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Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

AThe lower quartile is the 2nd value, 11 cm.
BThe upper quartile is the 6th value, 16 cm.
CThe interquartile range is 16 − 11 = 5 cm.

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Assemble a full-mark answer from its marking points, in the order an examiner wants them.

The sunspot cycle lasts about 11 years.
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Spot the fault in a statement. The traps are the mistakes students actually make.

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