Whether an animal eats plants or flesh, the carbohydrates, fats and proteins in the food it eats are generally giant molecules (see chapter 1). These need to be split up into smaller ones before they can pass into the blood and enter the cells to be used for energy or to make new cell constituents.
- Carbohydrates like cellulose, starch, and glycogen need to be split into glucose and other monosaccharides;
- Proteins need to be split into amino acids;
- Fats or lipids need to be split into fatty acids and glycerol.