7.15 Fish farming, invasive species and indicator species
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Give one advantage and two disadvantages of fish farming.
Mark scheme
- advantage: food for growing population / less pressure on wild fish (1)
- disadvantages, any two from: eutrophication from waste (1); spread of disease / parasites to wild fish (1); escaped fish compete with wild fish (1)
Model answer
Fish farms provide food without taking wild fish, but their waste causes eutrophication and diseases spread to wild fish.
Explain how the introduction of grey squirrels to the UK has affected red squirrels.
Mark scheme
- grey squirrels outcompete red squirrels (for food / space) (1)
- carry a disease (squirrel pox) that kills red squirrels (1)
Model answer
Grey squirrels outcompete red squirrels for food and carry a disease that kills them, so red squirrel numbers have fallen.
What is an indicator species?
Mark scheme
a species whose presence / absence shows the level of pollution
Model answer
An indicator species is one whose presence or absence shows how polluted an environment is.
A student finds many stonefly nymphs in a stream. What does this tell you about the water? Explain your answer.
Mark scheme
- the water is clean / unpolluted (1)
- stonefly nymphs need lots of (dissolved) oxygen (1)
Model answer
The water is clean, because stonefly nymphs can only survive in water with a lot of dissolved oxygen.
Explain why there are few types of lichen growing near a busy road in a city.
Mark scheme
- air contains sulfur dioxide (from burning fuels) (1)
- lichens are sensitive to / killed by sulfur dioxide (1)
Model answer
Vehicles release sulfur dioxide, and many lichens cannot survive in air containing sulfur dioxide.
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