Concept:Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration, down the concentration gradient.
Explanation:Digested food molecules are more concentrated in the small intestine than in the blood capillaries inside the villi.
Therefore, these molecules move into the villi by diffusion along the concentration gradient.
Opening and closing of stomatal pores is due to changes in turgidity of guard cells, not diffusion.
Turgidity in herbaceous plants results mainly from osmosis.
Absorption of water through root hairs is principally an osmotic process.
Thus, only the absorption of digested food into the villi directly involves diffusion.
Answer:D. Absorption of digested food into the villi