Answer:
Eating pizza provides the body with an external source of energy because it contains nutrients such as carbohydrates, fats, and proteins that can be broken down by the body's digestive system to release energy. Once these nutrients are absorbed into the bloodstream, they are transported to the body's cells where they are used as fuel to generate ATP (adenosine triphosphate), the primary energy currency of the body.
On the other hand, ATP is an internal source of energy because it is produced by the body's own metabolic processes. ATP is synthesized through cellular respiration, a series of chemical reactions that occur within the cells of the body. During this process, nutrients such as glucose are broken down to release energy, which is then used to synthesize ATP. Once formed, ATP can be used by the body's cells to power a wide range of biological processes such as muscle contraction, protein synthesis, and nerve impulse transmission.
In summary, external sources of energy such as food provide the raw materials that the body needs to synthesize ATP internally, which is then used as the primary source of energy for various cellular processes.
Step-by-step explanation: