Animals take in this oxygen and release it as carbon dioxide. It is the process of respiration that helps the animals to survive. Actually the oxygen is transferred to the blood and the cells and then the carbon oxide is transferred from the blood and cells to the lungs for breathing out. Carbon dioxide is a waste material for our body. The build up of carbon dioxide in the body can be very fatal and lead to death of the animal. It is actually the reverse in case of plants. Plants take in carbon dioxide for making food by the process of photosynthesis and gives out oxygen. So it is a balancing act between animals and plants.
