Respiration is of the mainly environmental responses an organism make in order to surivive. This is to maintain homeostasis, homeostasis is attained thru balancing both in the internal and external factors and if it isn't then a disorder can occur or maybe a specific antibody has infiltrated the organism.
An animal inhales oxygen and exhales carbon dioxide when it initiates respiration. This process is assissted by either the lungs in most animals -mammals etc. and gills by other organisms such as sharks, marine life and etc. This phenomenon is to attain and maintain homeostasis.