The term also describes all the processes associated with the release of energy in the body. The blood carries food and oxygen to the cells so they can produce energy for their needs. Oxygen is needed in the cells to break carbohydrates and fats into energy. Carbon dioxide is a byproduct of metabolism in the cells, but while it is a waste product in man and animals, carbon dioxide is necessary for plant respiration. Plants release oxygen, their waste product, and the cycle of mutual benefits between plant and man is repeated continuously.
Gas exchange occurs in the lungs.
The right side of the heart pumps blood with a high concentration of carbon dioxide into the lungs. The carbon dioxide is replaced with oxygen. The blood changes from a dark red to a bright red color, indicating hemoglobin has picked up the oxygen. The oxygen-enriched blood is pumped through the left side of the heart and then circulated throughout the body. The carbon dioxide is then exhaled.