Final answer:
Weight loss occurs when stored fat is metabolized through cellular respiration into carbon dioxide and water. The carbon dioxide is exhaled, and the water is excreted, which results in weight loss.
Step-by-step explanation:
Understanding Weight Loss through Cellular Respiration:
When your friend loses 15 pounds of fat, the weight is primarily lost through a process called cellular respiration. This biological process occurs in the mitochondria of cells, where fat molecules are broken down to release energy. The fat, which is composed mostly of carbon, hydrogen, and oxygen, is converted into carbon dioxide and water after reacting with oxygen. The carbon dioxide is then expelled from the body through the lungs when we exhale, and the water may be lost as urine, sweat, or other bodily fluids.
It is a common misconception that fat is mostly converted to energy or heat. Instead, a significant portion of the mass of the fat is released as carbon dioxide. The weight loss occurs as the body uses up the stored fat for energy and expels the by-products, illustrating the principle of conservation of mass.