A substance that is NOT an end product of digestion is:

Maltose is not an end product of digestion; instead, it is a disaccharide that needs to be broken down further into its constituent monosaccharides, glucose and glucose, before it can be absorbed into the bloodstream. Digestive enzymes, specifically maltase, facilitate this breakdown process to convert maltose into glucose.

In contrast, amino acids, fatty acids, and glucose are indeed end products of digestion. Proteins are broken down into amino acids, fats into fatty acids (and glycerol), and carbohydrates into simple sugars like glucose. These end products are then absorbed through the intestinal lining into the bloodstream and utilized by the body for various metabolic functions. Therefore, while maltose is an important carbohydrate in the digestive process, it does not represent the final stage of digestion, which is why it is identified as the correct answer in this context.