The reaction of cellular respiration and burning of fossil fuel needs carbon. Fossil fuel are like coal is made up of carbon. Organic compounds are made up of carbon(abundant), hydrogen and oxygen in small amounts.
The cellular respiration is the process by which the body obtains energy in the form of ATP by the breakdown of carbohydrates which is also a carbon compound.
In cellular respiration, a higher carbon molecule i.e glucose breaks down in the presence of oxygen to produce carbon dioxide, water and energy. The chemical equation for cellular respiration is given below –
C 6 H 12 O 6 + 6 O 2 --> 6 CO 2 + 6 H 2 O + ATP
Like wise, in combustion of any fuel , the higher carbon molecules burn in the presence of oxygen to release gases like carbon dioxide methane etc.