Final answer:
Digested food moves into the blood without the need for ATP because the absorption process, such as diffusion or facilitated diffusion, relies on a concentration gradient and does not require energy. Once absorbed, nutrients are used in cellular respiration to produce ATP, which powers cellular functions.
Step-by-step explanation:
Why does digested food move into the blood without the use of ATP? Digestion is the process where food is broken down into smaller components that can be absorbed into the bloodstream. During this process, nutrients like simple sugars from carbohydrates, amino acids from proteins, and fatty acids from fats are absorbed through the walls of the small intestine through processes such as diffusion or facilitated diffusion, which don't require energy from ATP. Transferring these nutrients to the blood is driven by the concentration gradient, a process that does not require energy, thus making the absorption of digested nutrients into the bloodstream metabolically efficient.
Cellular respiration begins once these absorbed monosaccharides are transported to the tissues, where glucose is oxidized in a process known as glycolysis to produce ATP. This is how cells obtain energy to perform functions. ATP is like a charged battery, used by cells for various activities, whereas digested food substances are absorbed passively without the need for this energy currency.