Simple diffusion is a biological process where molecules move from an area of higher concentration to an area of lower concentration without the need for energy or assistance from membrane proteins. It occurs naturally as molecules spontaneously spread out due to their random motion and the concentration gradient, typically across a semipermeable membrane such as a cell membrane. This process is considered passive transport because it does not require ATP or cellular energy expenditure.

Key Features of Simple Diffusion

• Molecules move down their concentration gradient (from high to low concentration).
• No energy (ATP) is required for the process.
• Does not require membrane proteins or carriers.
• Commonly involves small, nonpolar molecules such as oxygen, carbon dioxide, and lipids.
• Achieves equilibrium where the concentration is uniform on both sides of the membrane.

Comparison with Facilitated Diffusion

• Simple diffusion is unassisted, while facilitated diffusion requires membrane proteins.
• Both move substances down the concentration gradient but differ in their mechanisms.

Biological Importance

Simple diffusion helps in the transport of gases and small molecules essential for cellular metabolism and homeostasis. It allows cells to acquire nutrients and release waste efficiently without energy costs. This explanation summarizes the fundamental concept and characteristics of simple diffusion in biological systems.