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?

1. 1 and 4 only
2. 2 and 3 only
3. 2, 3 and 4 only
4. 1, 2 ,3 and 4

Explanation

Option (c) is correct

• Carbon is a minor constituent of the atmosphere as compared to oxygen and nitrogen. However, without carbon dioxide, life could not exist because it is vital for the production of carbohydrates (photosynthesis) by plants and phytoplankton.
• Carbon is the element that anchors all organic substances from coal and oil to DNA (deoxyribonucleic acid: the compound that carries genetic information).
• Steps in the Carbon Cycle
  • The carbon cycle involves a continuous exchange of carbon between the atmosphere and organisms. This is usually a short-term cycle.
  • Carbon is present in the atmosphere, mainly in the form of carbon dioxide (CO2). Carbon from the atmosphere moves to green plants and phytoplankton through photosynthesis and then to animals.
  • Through the process of respiration and decomposition of dead organic matter, it returns to the atmosphere
    • The decomposition of decaying organic matter produces nitrogen and carbon dioxide.
    • Organic matter includes biomolecules (carbohydrates, proteins, etc.), which are made up of carbon, oxygen, hydrogen, and nitrogen.
  • Some carbon enters a long-term cycle. It accumulates as undecomposed organic matter in the peaty layers of marshy soil or as insoluble carbonates in the bottom sediments of aquatic systems, which take a long time to be released.
  • In deep oceans, insoluble carbon can remain buried for millions of years until geological movements lift these rocks above sea level. These rocks may then be exposed to erosion, releasing their carbon dioxide, carbonates, and bicarbonates into streams and rivers.
  • Fossil fuels such as coal, oil and natural gas are organic compounds that were buried before they could be decomposed and were subsequently transformed by time and geological processes into fossil fuels. When they are burned, the carbon stored in them is released back into the atmosphere as carbon dioxide.

Answer: (c) 2, 3 and 4 only | Difficulty Level: Easy