Energetics of the Reactions
How does energy get passed on?
A fascinating thing between plant and animal life is that the cells handle the energy transformation processes necessary for life in the use of tiny energy factories. In plants, these energy factories are called chloroplasts. They collect energy from the sun and produce sugars using carbon dioxide and water in the photosynthesis process. Animals can make use of the sugars provided by the plants in their own cellular energy factories, the mitochondria. These produce a versatile energy which the body can use in the form of adenosine triphosphate, also known as ATP. This high-energy molecule stores the energy we need to do just about everything we do from running, talking or on the molecular level, cells making copies of themselves.
How much energy is passed on?
The answer to this question depends on what is being referred to. There are many ways in which ATP is used in our bodies, from the synthetic level (the production of DNA - your genetic material) to the mechanical level (movement of muscles). Both of these require a lot of ATP. Through the process of cellular respiration the body breaks down glucose, the source of ATP. The amount of ATP gained in an aerobic respiration (meaning that the animal used the oxygen in the air), one molecule of glucose yields 38 ATP molecules, eight produced during glycolysis (metabolic pathway that converts glucose into pyruvate which realeases free energy used to form ATP). The net gain, however, is 36 ATP, as two of the ATP molecules produced from glycolysis are used up in the re-oxidation of the hydrogen carrier molecule NAD.