Final answer:
The body uses enzymes for the chemical digestion of food, breaking down nutrients such as carbohydrates, proteins, and lipids into smaller molecules like simple sugars, amino acids, and fatty acids, which can be absorbed and utilized by the cells.
Step-by-step explanation:
Substances that help the body break down nutrients into a smaller usable form are primarily enzymes involved in chemical digestion. These enzymes catalyze the breakdown of large, complex food molecules into simpler nutrient molecules. For example, carbohydrates are broken down into simple sugars, proteins into amino acids, and lipids into fatty acids and glycerol. These smaller molecules can then be absorbed by the bloodstream or lymph and utilized by the body's cells.
Consider the digestive process: After you chew and swallow your food, enzymes in the saliva, stomach, and intestines work to break down the food. Salivary amylase, for instance, starts the digestion of carbohydrates in the mouth, while pepsin in the stomach begins the digestion of proteins. The majority of chemical digestion, however, takes place in the duodenum of the small intestine, where pancreatic enzymes and bile further dismantle the nutrients.
Nutrients such as carbohydrates, proteins, and lipids are essential because they provide energy and the building blocks for new cellular components. Once digested, they contribute to cellular metabolism, allowing the conversion of these nutrients to adenosine triphosphate (ATP), the energy currency of cells.