What substances are absorbed via passive diffusion throughout the small intestine?

Passive diffusion is a process where substances move across cell membranes from an area of higher concentration to an area of lower concentration without the need for energy. In the context of the small intestine, certain substances are particularly well-suited for passive diffusion due to their molecular nature and the environment within the intestinal tract.

Water and lipids are absorbed via passive diffusion as they can easily pass through the lipid bilayer of cell membranes. Water, being a small molecule, can traverse the intestinal lining rapidly. Lipids, which are hydrophobic, also move through cellular membranes effectively because the membranes themselves are primarily composed of phospholipids.

Minerals and vitamins, while some can be absorbed through facilitated diffusion and active transport, do not predominantly rely on passive diffusion. Similarly, carbohydrates and sugars typically require specific transport mechanisms due to their larger structures and polar characteristics. Proteins and fibers, being larger macromolecules, cannot pass through cell membranes via passive diffusion.

Thus, the absorption of water and lipids throughout the small intestine via passive diffusion stands out as the correct response to the question.