Final answer:
Animals rid themselves of carbon dioxide produced by cellular respiration using organs like lungs or gills. This CO2 is transported via the circulatory system to these organs and then expelled as part of the breathing process.
Step-by-step explanation:
Animals eliminate carbon dioxide (CO2) produced in their cells by respiration through various respiratory systems adapted to their environment and size. Small organisms or those with flattened bodies often rely on simple diffusion to remove CO2, as the distances for diffusion are short enough for this process to be efficient. In contrast, larger organisms have evolved more complex respiratory organs, like gills or lungs, and accompanying circulatory systems to transport CO2 to these organs where it can be expelled from their body.
For instance, in humans, CO2 travels from the cells where it's produced, is converted into bicarbonate in the red blood cells, and carried to the lungs. Once in the lungs, the bicarbonate is converted back into CO2 by an enzyme called carbonic anhydrase, and it is then exhaled as part of the breathing process. Similarly, aquatic animals with gills extract oxygen from water and expel CO2 into the water. This process of gas exchange is crucial for maintaining the physiological balance and is part of the broader carbon cycle, which also includes photosynthesis and decomposition.