Final answer:
Water is absorbed without digestion in both the stomach and the large intestine, but most nutrient molecules are absorbed in the small intestine.
Step-by-step explanation:
The substance that is absorbed without digestion is water. While the majority of nutrients require digestion to break them into simple molecules suitable for absorption, water is an exception and can be absorbed directly. This absorption of water occurs in both the stomach and the large intestine, but it is important to note that about 95% of nutrient molecules are absorbed in the small intestine, with specific areas like the jejunum, duodenum, and ileum specializing in the absorption of different nutrients.