Combustion

Combustion is burning: a fuel reacts with oxygen and releases energy to the surroundings. It is an exothermic reaction. This energy transfer is why hydrocarbon fuels can be used for heating, cooking and powering engines.

Carbon moves into plants through photosynthesis, passes between organisms through feeding, and returns to the atmosphere through respiration and combustion. A material cycle is therefore a network of routes, not necessarily one simple loop.