Which of the following adds/add carbon dioxide to the carbon cycle on the planet Earth? 1. Volcanic action 2. Respiration 3. Photosynthesis 4. Decay of organic matter Select the correct answer using the code given below.
- (a) 1 and 3 only
- (b) 2 only
- (c) 1, 2 and 4 only ✓ UPSC's answer
- (d) 1, 2, 3 and 4
Why the answer is (c)
• Volcanic eruptions (1) release CO2 from the Earth's interior; respiration by plants, animals and microbes (2) releases CO2 from breaking down glucose; decay of organic matter (4) by decomposers returns carbon to the air as CO2.
• Photosynthesis (3) does the opposite — it removes CO2 from the atmosphere to build carbohydrates.
• Hence 1, 2 and 4 only, option (c).
Why the other options are wrong
- (a) 1 and 3 only
- Photosynthesis removes CO2; respiration and decay add it.
- (b) 2 only
- Volcanic action and decay also add CO2.
- (d) 1, 2, 3 and 4
- Photosynthesis absorbs, not adds, CO2.
Asked in the GS Paper I of the UPSC Civil Services Preliminary Examination 2014, held on 24 August 2014. Question and answer key: Union Public Service Commission. Explanation: UPSC Answer Check.