Which of the following statements is correct about diffusion? a. It is very rapid over long distances. b. It requires an expenditure of energy by the cell. c. It is a passive process in which molecules move from a region of higher concentration to a region of lower concentration. d. It is an active process in which molecules move from a region of lower concentration to one of higher concentration. e. It requires integral proteins in the cell membrane.

Diffusion is often celebrated for its elegant simplicity! It occurs naturally as molecules spread out to achieve equilibrium, meaning they move from areas of high concentration to areas of low concentration without any energy input. Think of it like watching a drop of dye swirl gracefully through water until the color is evenly distributed—nature's way of achieving balance! In terms of real-world application, diffusion isn't just a textbook concept; it's happening all around us! For example, it plays a crucial role in how our lungs function. When you inhale, oxygen moves from the air (high concentration) into your bloodstream (low concentration) via diffusion, while carbon dioxide travels in the opposite direction. This vital process keeps us alive every single day!