"If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys."Which one of the following functions of wetlands best reflects the above statement?

1. A

   The water cycle in wetlands involves surface runoff, subsoil percolation and evaporation.

   Water cycle. Hydrology, not the kidney metaphor.

2. B

   Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles and mammals thrive.

   Food web. Lungs/energy, not filtration.

3. C

   Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.

   Sediment and soil. A wetland job, but not the ‘kidney’ line as keyed.

4. D

   Aquatic plants absorb heavy metals and excess nutrients.

   Plants absorbing heavy metals and excess nutrients. That is the filter / kidney function.

Summary. Official key is (d). Wetlands as ‘kidneys’ is the water-quality job: plants and soils strip nutrients and metals. Runoff, food webs and bank stability are other wetland roles.