7.7 The water cycle
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Name the process by which water vapour is lost from the leaves of plants.
Mark scheme
transpiration
Model answer
Transpiration.
Describe how water in the sea becomes rain falling on land.
Mark scheme
- water evaporates (heated by the Sun) (1)
- water vapour condenses / cools to form clouds (1)
- falls as precipitation (1)
Model answer
Energy from the Sun makes sea water evaporate. The water vapour rises, cools and condenses into clouds, and then falls as rain (precipitation).
Explain why rain is fresh water even though it evaporated from the salty sea.
Mark scheme
salt does not evaporate / is left behind when water evaporates
Model answer
Only the water evaporates; the salt is left behind in the sea.
Describe the steps in making reservoir water safe to drink.
Mark scheme
- sedimentation (1)
- filtration (through sand / gravel) (1)
- chlorination / sterilising to kill microorganisms (1)
Model answer
The water is left so particles settle out (sedimentation), filtered through sand and gravel, and chlorinated to kill microorganisms.
Give one method of desalination and one disadvantage of it.
Mark scheme
- distillation / reverse osmosis (1)
- needs a lot of energy / expensive (1)
Model answer
Distillation, which uses a lot of energy and so is expensive.
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