Pollution & waste

Answer: (c) 1 and 3 only

Bioremediation speeds up the natural breakdown of pollutants by microbes, and microbes can be genetically engineered for the job. But microbes break down organic compounds; metals such as cadmium and lead are elements that cannot be degraded, only changed in form or immobilised, so statement 2 overclaims.

• ✓ 1. It uses microorganisms that feed on or co-metabolise contaminants, boosting the same biodegradation that happens in nature by supplying nutrients, oxygen or other electron acceptors.
• ✗ 2. Bioremediation is described as degrading organic contaminants. Heavy metals cannot be broken down by microbes, so 'readily and completely treated' is wrong; at best microbes change their chemical form.
• ✓ 3. Biotechnology uses genetically modified microbes for bioremediation; in 1971 Ananda Mohan Chakrabarty developed a bacterium that could break down oil spills.

Remember · Bioremediation = microbes degrading organic pollutants (oil, solvents, pesticides); engineered microbes help. Heavy metals cannot be degraded, only transformed or immobilised.

📘 Read it in NCERT: Class 12 Biology, Ch 10 (practise this chapter) · Class 8 Curiosity, Ch 2 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (c) Pollution assay in aquatic ecosystems

BOD is the amount of oxygen that bacteria would use up to break down the organic matter in a sample of water, so it is a standard test of how polluted water is. A higher BOD means more organic pollution.

• ✓ (c) BOD measures the oxygen consumed by microbes in decomposing the organic matter in water, so it works as an indirect measure of that matter. The greater the BOD of waste water, the greater its polluting potential.
• ✗ (a) BOD is a test on water samples. It has nothing to do with the oxygen carried in blood.
• ✗ (b) BOD says nothing about oxygen in forests. It tells us how much oxygen microbes need in water that carries organic waste.

Remember · BOD is oxygen bacteria need to decompose the organic matter in water. Higher BOD means more pollution; sewage treatment aims to bring it down.

📘 Read it in NCERT: Class 12 Biology, Ch 8 (practise this chapter) · Class 12 Biology, Ch 8 (practise this chapter)

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error

Answer: (b) 2 only

The Climate and Clean Air Coalition (CCAC) is a voluntary partnership convened within the UN Environment Programme (UNEP), not an initiative of the G20, so statement 1 is wrong. It targets methane, black carbon and hydrofluorocarbons, so statement 2 is correct.

• ✗ 1. The CCAC was founded in 2012 and is convened within UNEP. It is a voluntary partnership of governments, intergovernmental organisations and non-governmental organisations, not a project of the G20 group.
• ✓ 2. The CCAC works to cut short-lived climate pollutants: methane, black carbon, hydrofluorocarbons and tropospheric ozone. These stay in the air only briefly but heat the planet strongly and harm air quality.

Remember · CCAC (2012) is a UNEP-convened voluntary coalition on short-lived climate pollutants: methane, black carbon, HFCs and tropospheric ozone. It is not a G20 body.

Question and answer: UPSC's official GS Paper I (2017, Series A) — paper ↗ · answer key ↗. Explanation: Minimalist IAS, checked 30 Sept 2026 (how we verify). Permalink · Report an error