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When animals exercise, their muscles need more oxygen, which leads to an increase in oxygen consumption. Because smaller species have a greater surface area to body weight ratio, they have a greater surface for heat loss and less heat storage capacity so they need higher basal metabolism to generate more heat. This difference is largely due to the metabolic requirements necessary to maintain constant body temperature. For example, the 20-gram mouse consumes six times more oxygen per unit body mass than does a 70-kg pig. The consequence of this relationship is that smaller species consume more oxygen per kilogram of body weight than do larger species.
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Basal metabolism, the metabolism of the resting animal, is a function of metabolic body weight (M 0.75). Oxygen consumption and carbon dioxide production vary with the metabolic rate, which is dependent on the animal’s level of activity. The respiratory system provides oxygen (O 2) to support tissue metabolism and removes carbon dioxide (CO 2). The Respiratory System’s Primary Function Is the Transport of Oxygen and Carbon Dioxide Between the Environment and the Tissues
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