UPSC Prelims 2011 question on Carbon Cycle Sources

Statement by statement

1. Photosynthesis — Incorrect
Green plants, algae, and some bacteria absorb carbon dioxide from the atmosphere and use sunlight to prepare food. Thus, photosynthesis acts as a carbon sink, reducing atmospheric CO₂.

2. Respiration — Correct
Plants, animals, humans, and microbes break down glucose to release energy. During this process, carbon dioxide is released back into the atmosphere.

3. Decay of organic matter — Correct
When dead plants and animals decompose, bacteria and fungi break down their organic matter. This releases stored carbon mainly as CO₂ through microbial respiration.

4. Volcanic action — Correct
Volcanoes release gases from the Earth’s interior, including carbon dioxide, water vapour, and sulphur dioxide. Hence, volcanic activity adds geological carbon to the atmosphere.

Extra UPSC Info
Photosynthesis = Carbon sink
Respiration and decay = Biological carbon cycle
Volcanic action = Geological carbon cycle
Major human sources of CO₂ include fossil fuel burning, cement production, and deforestation.
Oceans are also major carbon sinks, absorbing large amounts of atmospheric CO₂.
Final Takeaway

Photosynthesis removes CO₂, while respiration, decomposition, and volcanic activity release CO₂. Therefore, the correct answer is 2, 3 and 4 only.