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There are five major components of air: nitrogen (78.0842%), oxygen (20.9463%), water vapor (about 1%), argon (0.93422%), and carbon dioxide (0.03811%). Trace components of air make up another 0.002%. Out of all the components of air, the one that animals (including humans) need to survive is oxygen, while the components of air that plants require are carbon dioxide and nitrogen. The respiration of animals consumes oxygen and produces carbon dioxide as a byproduct, while plants consume carbon dioxide and produce oxygen. The world's ecosystems depend on this balance. The components of air may be altered by human activity, such as the burning of fossil fuels, which has increased the proportion of carbon dioxide in the atmosphere.