Key Idea: Most of the carbohydrates, fats, and proteins from the food humans eat must be broken down into smaller molecules before they can enter cells to be used for energy and building materials.

Students are expected to know that:

  1. Most of the food that humans eat is made up of large molecules (fats, proteins, and complex carbohydrates) that are too big to get to the cells of the body where they can be used for energy and building materials.
  2. These large molecules are made up of subunits, which are smaller molecules of the same type that are linked together.Fatty acids are subunits of fats, amino acids are subunits of proteins, and simple sugars are subunits of complex carbohydrates.Carbon dioxide is not a subunit of fats, proteins, or complex carbohydrates.
  3. Some molecules from food (e.g., simple sugars, fatty acids, and amino acids) are already small enough to get to the cells of the body without being broken down into smaller molecules.
  4. Digestion is the process of breaking larger molecules into their subunits. The subunits are called the products of digestion.
  5. Digestion does not include the breaking down of food into molecules of carbon dioxide and water.
Boundaries:
  1. Students are not expected to know that glycerol is also a subunit of fats.
  2. Students are not expected to know the chemical formulas of complex carbohydrates, fats, proteins, simple sugars, fatty acids, or amino acids.
  3. Students are not expected to know the term “macromolecules.”