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📌 The Question:

“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?

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

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✅ Correct Answer: (d) Aquatic plants absorb heavy metals and excess nutrients

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🧠 Classroom Explanation:

Rainforests are metaphorically called the “lungs of the Earth” because they absorb carbon dioxide and release oxygen.

Similarly, wetlands are called the “kidneys of the Earth” because they filter, detoxify, and purify water, just as kidneys cleanse blood.

• Wetlands trap sediments
• Aquatic plants absorb excess nutrients such as nitrogen and phosphorus
• They remove heavy metals and pollutants from water
• This prevents eutrophication and downstream water contamination

Thus, the pollution-filtering function of wetlands best justifies the analogy of kidneys.

Options (a), (b), and (c) describe hydrological, ecological, or geomorphological roles, but not the detoxification role implied by “kidneys”.

Hence, option (d) is correct.

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🔍 Curiosity Raiser:
Why are constructed wetlands increasingly used as natural wastewater treatment systems in urban planning?

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📚 Enrich Notes (UPSC Edge):

• Wetlands act as nutrient sinks
• Reduce nitrate & phosphate load in rivers
• Mitigate heavy metal toxicity
• Key ecosystem service under Ramsar Convention
• Frequently asked in metaphor-based UPSC Prelims questions

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🪶 IAS Monk Whisper:
What lungs do for air, wetlands silently do for water — without applause.