The molecules that can diffuse from the digestive tract into the human bloodstream without first being digested are:
- a. water
- glucose
Water can easily diffuse across cell membranes, and glucose can be absorbed directly into the bloodstream without the need for prior digestion.
On the other hand, proteins (b), fats (c), and starch (d) must be broken down into smaller units (amino acids for proteins, fatty acids and glycerol for fats, and simple sugars for starch) before they can be absorbed into the bloodstream.