Simple Diffusion vs Facilitated Diffusion

The key difference between simple diffusion and facilitated diffusion is the difference of transport proteins.

In simple diffusion, molecules passively move down their concentration gradient directly through the plasma membrane without any help. While in facilitated diffusion, the transport of molecules occurs by the use of integral membrane proteins that form selective channels or carriers.

Although both processes are passive along an existing concentration gradient, facilitated diffusion involves proteins that lower activation energy and rapidly transport molecules that otherwise could not effectively cross the membrane.

Difference Between Simple Diffusion and Facilitated Diffusion

Here are the main differenc between Simple Diffusion and Facilitated Diffusion:

Feature	Simple Diffusion	Facilitated Diffusion
Definition and Mechanism of Transport	Molecules move straight through the lipid bilayer without help.	Molecules move through transport proteins in the membrane.
Primary Driving Force (Concentration Gradient)	Movement happens because molecules move from high to low concentration.	Movement also follows the concentration gradient but through proteins.
Energy Requirement (Passive Transport)	No ATP is used because it is passive.	No ATP is used because it is also passive.
Rate of Transport (Speed of Movement)	The speed is slower and depends only on the gradient.	The speed is faster at first but can slow when all proteins are busy.
Solute Specificity	It is not specific; any small non-polar molecule can move through.	It is specific because each protein helps certain molecules only.
Role of Kinetic Energy	Molecules move because of their natural kinetic energy.	Molecules also move due to kinetic energy but need protein support.
Inhibition by Specific Molecules	It cannot be blocked because no proteins are used.	It can be blocked when inhibitor molecules attach to transport proteins.
Direction of Particle Movement	Molecules move from high concentration to low concentration.	Molecules also move from high to low concentration.
Type of Molecules Transported (Size and Polarity)	Moves small, non-polar molecules like O₂, CO₂, and urea.	Moves large, polar, or charged molecules like glucose, Na⁺, and Cl⁻.
Passage Route Across Membrane	Molecules pass directly through the phospholipid bilayer.	Molecules pass through channel proteins or carrier proteins.
Examples	Gas exchange in lungs, perfume smell spreading, CO₂ leaving cells.	Glucose transport into cells and movement of ions through channels.

MCQs

The difference between simple diffusion and facilitated diffusion is that facilitated diffusion:

A. Requires ATP
B. Uses carrier proteins or channel proteins
C. Moves molecules against the concentration gradient
D. Transports O₂ directly through the membrane

Correct Answer: B

Facilitated diffusion is a type of:

A. Active transport
B. Bulk flow
C. Passive transport
D. Osmosis

Correct Answer: C

Simple and facilitated diffusion differ because:

A. They move in opposite directions
B. Facilitated diffusion needs transport proteins
C. Simple diffusion uses ATP
D. Facilitated diffusion changes cell volume

Correct Answer: B

In simple diffusion vs facilitated diffusion, a molecule that moves by simple diffusion is usually:

A. Large and polar
B. Small and non-polar
C. An ion that needs a channel
D. Moving against its gradient

Correct Answer: B

How are simple and facilitated diffusion different? One difference is that:

A. Simple diffusion is always faster
B. Facilitated diffusion can be saturated when proteins are full
C. Simple diffusion requires channel proteins
D. Facilitated diffusion needs ATP

Correct Answer: B

True/False

Simple diffusion and facilitated diffusion both require transport proteins to move molecules.
Answer: False
(Only facilitated diffusion needs proteins.)

Simple and facilitated diffusion are related in that both move molecules down the concentration gradient without using ATP.
Answer: True

Facilitated diffusion differs from ordinary (simple) diffusion in that it can be inhibited by specific molecules blocking the transport proteins.
Answer: True

Facilitated diffusion is the same as simple diffusion because both processes can be saturated.
Answer: False
(Only facilitated diffusion becomes saturated.)

What distinguishes simple diffusion from facilitated diffusion is that simple diffusion mainly moves small, non-polar molecules, while facilitated diffusion moves larger, polar, or charged molecules.
Answer: True

FAQs