What is diffusion? Select one option:

• A: The net movement of water molecules from a dilute solution to a concentrated solution through a partially permeable membrane.
• B: The movement of solute particles from a region of low concentration to a region of high concentration.
• C: The net movement of particles from a region of higher concentration to a region of lower concentration.

The human lungs contain millions of microscopic air sacs called alveoli. Describe how this feature increases the rate of diffusion of oxygen into the blood.

Complete the sentences below about the healing of damaged respiratory tissue:

• To replace damaged tissue and grow new cells, stem cells in the lungs divide by the process of $[blank\; 1]$.
• When these stem cells specialize to become functional epithelial cells, this process is known as $[blank\; 2]$.