Briefly describe how carbon moves through ecosystems via photosynthesis, respiration, and decomposition.

• A. Plants take in CO2 during photosynthesis to build biomass; animals respire releasing CO2; decomposers release CO2 back to the atmosphere when breaking down dead matter.
• B. CO2 is generated only by combustion; photosynthesis uses CO2.
• C. CO2 is stored in soils indefinitely.
• D. Carbon cycles only through oceans.

Answer: (A)

Carbon moves through ecosystems in a cycle that connects the atmosphere, living organisms, and soils. Plants take in carbon dioxide from the air during photosynthesis to build sugars and biomass. When plants and animals use that carbon for energy, they release carbon dioxide back into the air through respiration. When organisms die, decomposers such as bacteria and fungi break down the dead matter and release carbon back to the atmosphere as CO2 (and some carbon may become part of soil organic matter). This ongoing exchange keeps carbon cycling among air, living things, and soils, with carbon stored temporarily in biomass and soils before moving again. The other ideas don’t fit because carbon is not generated only by burning, photosynthesis does use CO2, carbon is not stored indefinitely in soils, and carbon also moves through oceans and land, not just oceans.