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.
Answer & explanation
Answer: (c) 1, 2 and 4 only
Volcanic action, respiration and decay of organic matter all release carbon dioxide into the atmosphere. Photosynthesis does the opposite: plants take CO2 out of the air to make glucose. So only 1, 2 and 4 add CO2.
- ✓ 1. Volcanoes are part of the slow carbon cycle. When they erupt, they vent carbon dioxide to the atmosphere.
- ✓ 2. Living organisms release CO2 back into the atmosphere through respiration.
- ✗ 3. Photosynthesis removes CO2 from the atmosphere. Plants use it with sunlight to make glucose, so it draws carbon dioxide out of the air rather than adding it.
- ✓ 4. When plants and animals die, decomposition returns their carbon to the air as CO2.
- ✗ (a) It leaves out respiration and decay, and wrongly includes photosynthesis.
- ✗ (d) It counts photosynthesis as a source of CO2, but photosynthesis removes CO2 from the air.
Remember · Sources of atmospheric CO2 include respiration, decomposition, volcanoes and fossil-fuel burning. Photosynthesis is the main biological process that removes CO2 from the air.
📘 Read it in NCERT: Class 9 Exploration, Ch 13 (practise this chapter)
Sources
- NCERT Class 9 · Exploration, Chapter 13 “CO2 is released back into the atmosphere through respiration. Animals eat plants and/or other animals. When they die, CO2 returns to air because of decomposition.”
- NASA Earth Observatory: The Carbon Cycle ↗ “When volcanoes erupt, they vent the gas to the atmosphere and cover the land with fresh silicate rock to begin the cycle again.”
Question: UPSC Civil Services (Preliminary) 2014, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·
