"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?

"If rainforests and tropical forests are the lungs of the Earth, then…

The water cycle in wetlands involves surface runoff, sub-soil percolation and evaporation.
Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles and mammals thrive.
Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.
Aquatic plants absorb heavy metals and excess nutrients.

Answer

(a) Wetlands do involve runoff, percolation and evaporation, but this describes hydrological processes, not the 'kidney' function of filtering wastes. Verdict: Incorrect.
(b) This explains wetlands as highly productive ecosystems supporting food webs, not as purifiers. Verdict: Incorrect.
(c) Sediment trapping and soil stabilization are important ecological functions, but the 'kidney' analogy mainly refers to cleansing/filtering. Verdict: Incorrect.
(d) Wetlands remove pollutants: aquatic plants and wetland systems absorb heavy metals and excess nutrients, improving water quality. This best matches the 'kidneys of the Earth' idea. Verdict: Correct.