What is diffusion? Select one option:

• A: The active transport of solute molecules up a concentration gradient.
• B: The net movement of water molecules from a dilute solution to a concentrated solution across a partially permeable membrane.
• C: The net movement of particles from an area of higher concentration to an area of lower concentration.

The lining of the small intestine contains millions of microscopic, finger-like folds called villi. Describe how this feature increases the rate of diffusion of soluble nutrients into the blood.

Complete the sentences below about the regeneration of the intestinal lining:

• To produce new epithelial cells for the regenerating lining, stem cells in the intestinal crypts divide by the process of $[blank\; 1]$.
• When these newly produced cells become specialized to perform absorption or secretion, this process is known as $[blank\; 2]$.