The
correct answer is D. when they are eaten by animals.
Carbon
cycle includes movement of CO2 from the atmosphere, through various organisms,
then back into the atmosphere again.
Plants (or algae or bacteria) use atmospheric
CO2 from the atmosphere, to generate oxygen through the process of photosynthesis.
The carbon then becomes part of molecules like proteins, fats and
carbohydrates. Passing carbon from one organism to the next occurs when an
animal eats a plant or when microorganisms and some animals feed on waste
material from animals or dead animals and plants (detritus feeders). CO2 gets
back to the atmosphere by respiration of animals, plants, algae and
microorganisms.
It can also be released into the atmosphere
when fossil fuels are burned.
