Oxygen and Carbon Dioxide Cycle + Water Cycle

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Oxygen Carbon Dioxide Cycle
Why is there always oxygen and carbon dioxide in
the air?
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• Living things need a constant supply of oxygen
  and carbon dioxide in the air to survive. They
  also constantly give out carbon dioxide. Oxygen
  in the air never runs out, and the air is never
  completely filled with carbon dioxide due to the
  oxgyen and carbon dioxide cycle.

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Oxygen in the air

• The air will not run out of oxygen as long as
  there are plants on the Earth. When plants make
  food during photosynthesis, oxygen is produced
  and released into the air. In this way, oxygen
  used up by living things is replaced constantly.

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Carbon dioxide in the air

• Living things like animals, give out carbon
  dioxide during respiration. Carbon dioxide is
  also released into the air when lixing things die
  and decay, or when Man burns oil or fussil fuels.
  Plants use carbon dioxide during photosynthesis.

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Water Cycle
What processes take place to ensure we always
have water on the Earth ?
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• Water never runs out on the Earth due to the
  wather cycle. The water cycle is the continuous
  movement of water from the Earth. Movement of
  water in the water cycle requires heat from the
  Sun to take place.

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Rising into the sky

• The Sun causes water from the lakes, river,
  reservoirs and surfaces of the ground to
  evaporate into the air. Living things also
  release water as water vapour into the air as
  they breath out. They also release water into the
  air when perspiration evaporates from their body.