Which natural process acts as a sink by removing carbon dioxide from the atmosphere?

• A. Photosynthesis
• B. Respiration
• C. Combustion
• D. Nitrogen fixation

Answer: (A)

The process that removes carbon dioxide from the atmosphere is photosynthesis. In photosynthesis, plants, algae, and some bacteria use light energy to convert CO2 and water into glucose and oxygen. This carbon from CO2 becomes part of the organic molecules in plant tissues and soils, effectively pulling CO2 out of the air and storing it as biomass and organic matter. This is why photosynthesis acts as a natural sink for atmospheric carbon.

In contrast, respiration releases CO2 back into the atmosphere as organisms convert stored organic carbon back into energy. Combustion burns carbon-containing fuels, releasing CO2 rather than sequestering it. Nitrogen fixation changes atmospheric nitrogen gas into bioavailable forms and does not involve converting CO2, so it doesn’t remove atmospheric carbon.