Consider the following:
- 1.Photosynthesis
- 2.Respiration
- 3.Decay of organic matter
- 4.Volcanic action
Which of the above add carbon dioxide to the carbon cycle on Earth?
Answer & explanation
Answer: (c) 2, 3 and 4 only
Respiration, decay of organic matter and volcanic action all release CO2 into the atmosphere. Photosynthesis does the opposite: it takes CO2 out of the air to make glucose. So 2, 3 and 4 add CO2, and the answer is (c).
- ✗ 1. Photosynthesis removes CO2 from the atmosphere. Plants use sunlight to turn CO2 into glucose, so the process takes CO2 out of the air instead of adding it.
- ✓ 2. During respiration, living things break down sugar with oxygen. This releases CO2, water and energy, and the CO2 goes back into the atmosphere.
- ✓ 3. When dead plants and plankton decay, bacteria break them down. As in respiration, oxygen combines with sugar and releases CO2.
- ✓ 4. In the slow carbon cycle, carbon locked in rock deep inside the Earth is released as CO2. Volcanic eruptions vent this gas into the atmosphere.
Remember · Photosynthesis removes CO2 from the air. Respiration, decay, burning and volcanic eruptions add it. Volcanoes return CO2 to the atmosphere in the slow carbon cycle.
📘 Read it in NCERT: Class 9 Exploration, Ch 13 (practise this chapter)
Sources
- NCERT Class 9 · Exploration, Chapter 13 “plants convert atmospheric CO2 into glucose using sunlight through photosynthesis. CO2 is released back into the atmosphere through respiration.”
- NASA Earth Observatory – The Carbon Cycle ↗ “Plants and plankton die and decay (are eaten by bacteria) at the end of the growing season. Or fire consumes plants. In each case, oxygen combines with sugar to release water, carbon dioxide, and energy. … 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) 2011, General Studies Paper I. Explanation: Minimalist IAS, checked 25 Oct 2026 (how we verify). ·
