Which biotic component is directly responsible for returning carbon to the atmosphere during respiration and decomposition?

• A. Dead biomass
• B. Plants
• C. Living organisms
• D. Soil bacteria

Answer: (C)

In the carbon cycle, carbon is returned to the atmosphere through respiration and decomposition by living organisms. When cells respire, they break down sugars to release energy and CO2. Decomposition is carried out by decomposers (microbes like bacteria and fungi) that break down dead matter and also release CO2 as part of their metabolism. Dead biomass itself is just the material being broken down, not the agent causing the release. While soil bacteria are a type of living organism, the broad category of living organisms covers all the beings that perform these processes, including plants, animals, and microbes, making it the best fit.