Correct Option
The processes that add carbon dioxide (CO₂) to the carbon cycle on Earth are respiration, decay of organic matter, and volcanic action.
- Respiration (Statement 2): All living organisms, including plants, animals, and microorganisms, release CO₂ into the atmosphere or water bodies as a byproduct of cellular respiration, where organic compounds are broken down to release energy.
- Decay of organic matter (Statement 3): When dead organic matter (plants and animals) decomposes, microorganisms (bacteria and fungi) break down complex organic compounds. This decomposition process involves microbial respiration, which releases CO₂ into the atmosphere.
- Volcanic action (Statement 4): Volcanic eruptions emit various gases from the Earth's interior, including significant amounts of carbon dioxide (CO₂), directly contributing to the atmospheric carbon pool.
Incorrect Options
- Photosynthesis (Statement 1): This process removes carbon dioxide from the atmosphere. Green plants, algae, and some bacteria utilize CO₂ from the atmosphere, along with water and sunlight, to synthesize organic compounds (sugars) and release oxygen. Therefore, photosynthesis acts as a carbon sink, not a source.
- Option (1) "1 and 4 only" is incorrect because photosynthesis removes CO₂, and it excludes respiration and decay of organic matter.
- Option (2) "2 and 3 only" is incorrect because it omits volcanic action (statement 4), which is a natural process that adds CO₂ to the atmosphere.
- Option (4) "1 and 4" is incorrect as it includes photosynthesis, which consumes CO₂, and excludes respiration and decay.