Simple Diffusion is defined as which of the following?

Simple Diffusion is defined as which of the following?

• A. Active Transport Requiring Energy To Move Substances
• B. Movement Of Water Through Aquaporins
• C. Movement Of Ions Through Channels
• D. Passive Transport Where Molecules Pass Through The Plasma Membrane Without Proteins

Answer: (D)

Simple diffusion is the passive movement of small, nonpolar molecules across the lipid bilayer down their concentration gradient without any energy input or transport proteins. Think of oxygen and carbon dioxide freely slipping through the membrane because they don’t carry charge and are small enough to dissolve in the lipid core. This is what makes it passive transport. The other options don’t fit because active transport requires energy to move substances against their gradient, not down it. Movement of water through aquaporins uses channel proteins, which means it’s osmosis or facilitated diffusion, not simple diffusion. Movement of ions through channels also relies on protein channels and is a form of facilitated diffusion (or, for active cases, active transport), not simple diffusion.

Simple diffusion is the passive movement of small, nonpolar molecules across the lipid bilayer down their concentration gradient without any energy input or transport proteins. Think of oxygen and carbon dioxide freely slipping through the membrane because they don’t carry charge and are small enough to dissolve in the lipid core. This is what makes it passive transport.

The other options don’t fit because active transport requires energy to move substances against their gradient, not down it. Movement of water through aquaporins uses channel proteins, which means it’s osmosis or facilitated diffusion, not simple diffusion. Movement of ions through channels also relies on protein channels and is a form of facilitated diffusion (or, for active cases, active transport), not simple diffusion.