Why do fibre molecules NOT diffuse through the small intestine wall?
Firstly, the fibre molecules don’t diffuse due to the fact that they are too large. As for the other question, there are a few ways to increase the rate of diffusion, and increasing the surface area is one of them. This is because the amount of particles passively moving from high to low concentrations can increase. Therefore, the rate improves and increases per second. This is done by the formation of villi in the small intestine, and surface area is further increased by microvilli, found in the epithelial cells in the small intestine. Also, carbon dioxide is removed as it diffuses from the red blood cells into the lungs across the capillaries, then to be exhaled out into the atmosphere.
