Which of the following best describes simple diffusion?

Which of the following best describes simple diffusion?

• A. Movement of specific molecules through protein channels
• B. Movement of water across a membrane
• C. Movement of particles from high to low concentration
• D. Movement of ions against a concentration gradient

Answer: (C)

Simple diffusion involves the movement of particles from an area of higher concentration to an area of lower concentration. This process occurs spontaneously as molecules spread out to evenly occupy a space, driven by the concentration gradient. It is a fundamental mechanism by which substances like oxygen and carbon dioxide pass through cell membranes without the need for energy or assistance from proteins. The primary characteristic of simple diffusion is that it does not require any special transport proteins or energy inputs, distinguishing it from other forms of transport such as facilitated diffusion, where specific molecules move through protein channels, or active transport, where ions move against their concentration gradient using energy. In this context, the correct description aligns with the basic principle of how simple diffusion operates, making it the best choice in the given question.

Simple diffusion involves the movement of particles from an area of higher concentration to an area of lower concentration. This process occurs spontaneously as molecules spread out to evenly occupy a space, driven by the concentration gradient. It is a fundamental mechanism by which substances like oxygen and carbon dioxide pass through cell membranes without the need for energy or assistance from proteins.

The primary characteristic of simple diffusion is that it does not require any special transport proteins or energy inputs, distinguishing it from other forms of transport such as facilitated diffusion, where specific molecules move through protein channels, or active transport, where ions move against their concentration gradient using energy. In this context, the correct description aligns with the basic principle of how simple diffusion operates, making it the best choice in the given question.