Question

diffusion can be described as...
the movement of molecules from an area of lower concentration to an area of higher concentration.
a form of transport that requires spending energy.
requiring a semipermeable membrane.
the movement of molecules from an area of higher concentration to an area of lower concentration.

Explanation:

• Option 1: Diffusion is from higher to lower concentration, not lower to higher. So this option is wrong.
• Option 2: Diffusion is a passive transport and does not require energy. Active transport requires energy. So this option is wrong.
• Option 3: Osmosis (a type of diffusion for water) across a semi - permeable membrane. But simple diffusion (e.g., gas diffusion in air) does not always require a semi - permeable membrane. So this option is too restrictive.
• Option 4: Diffusion is defined as the movement of molecules (or atoms or ions) from an area of higher concentration to an area of lower concentration due to their random thermal motion.

Answer:

the movement of molecules from an area of higher concentration to an area of lower concentration.