Concept:Carbon dioxide is returned to the atmosphere through biological activities that release it as a waste product.
Explanation:Respiration is the process by which living organisms break down glucose and other organic compounds to release energy.
This process produces carbon dioxide (
CO2) as a by-product and releases it into the atmosphere.
Plants, animals, and decomposers all respire continuously.
This means respiration steadily replenishes atmospheric carbon dioxide in the carbon cycle.
Transpiration is the loss of water vapour from plant leaves, not carbon dioxide.
Therefore, transpiration does not replenish atmospheric carbon dioxide.
Similarly, lightning helps fix atmospheric nitrogen into nitrates.
Denitrification converts nitrates into nitrogen gas.
Both lightning and denitrification are processes of the nitrogen cycle, not the carbon cycle.
Answer:A. respiration