UPSC Prelims 2014 Question:

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:

Explanation:

• A volcano is a vent in the Earth’s crust from which eruptions occur. There are about 1500 potentially active volcanoes worldwide. Volcanic eruptions can impact climate change through emitting volcanic gasses like sulfur dioxide, which causes global cooling, and volcanic carbon dioxide, which has the potential to promote global warming. So, point 1 is correct.
  
  
• Respiration is defined as a metabolic process wherein, the living cells of an organism obtain energy in the form of Adenosine Triphosphate (ATP) by taking in oxygen and liberating carbon dioxide from the oxidation of complex organic substances. So, point 2  is correct.
  
  
• Photosynthesis is the process by which plants use sunlight, water and carbon dioxide to create oxygen and energy in the form of sugar. So, point 3 is not correct.
  
  
• The decomposition of organic matter is largely a biological process that occurs naturally. Its speed is determined by three major factors: soil organisms, the physical environment, and the quality of the organic matter. In the decomposition process, different products are released: carbon dioxide (CO2), energy, water, plant nutrients, and resynthesized organic carbon compounds. Successive decomposition of dead material and modified organic matter results in the formation of a more complex organic matter called humus. So, point 4 is correct.
  
  

Therefore, option (3) is the correct answer.

Subject: Environment | Pollution