CAIE A Level Biology 9700 · Classification, biodiversity and conservation
A salt marsh is a coastal ecosystem that experiences tidal flooding. It has high salinity, waterlogged soil, and is dominated by cordgrass (Spartina alterniflora). The marsh periwinkle snail (Littoraria irrorata) grazes on algae on cordgrass stems, and uses the grass as a substrate to avoid predators. During high tide, the snail climbs up the grass to escape water.
Describe what is meant by the terms ecosystem and niche, using the salt marsh as an example.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Describe means: Say what happens or what something is like, in order and with detail. You are not being asked why. If there is data, quote it: name the trend, then give figures with units at the points where it changes.
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