Carbon cycle is the one of the biogeochemical cycles. It involves the circulation and distribution of carbon in atmosphere, hydrosphere, biosphere, lithosphere and other spheres of earth.
The two paths carbon dioxide can take through carbon cycle are:
1. Atmosphere to biosphere: The carbon dioxide is required by the plants as an important reactant of photosynthesis. The carbon dioxide is present in atmosphere in gaseous form. The plants are the part of biosphere.
2. Biosphere to lithosphere: The plants and animals dead and decaying material becomes the part of the lithosphere. As the soil microbes decompose the dead matter and liberates carbon dioxide in the soil. The soil is the part of the lithosphere.
They may have ran out of oxygen, or they may not have been water dwelling snails, as not all are, lack of food, no flow of water into and out of the tank would cause them to run out of oxygen.
Carbon can be continuously cycled, but energy cannot
Carbon in the feces of a top predator can be decomposed and used by primary producers in the form of CO2; the energy in the feces is used by the decomposers and is released as heat.
