A LITTLE LIGHTBULB MOMENT
Cell biology, genetics and molecular biology
Facilitated diffusion
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Membrane doors help tired molecules cross downhill
The idea behind the cue
Facilitated diffusion uses membrane proteins to move substances down their concentration gradient without ATP. It is specific and saturable because transport proteins can become occupied.
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Short & simple
Membrane doors help tired molecules cross downhill
Acronym
FGS — Fluffy Goats Snore.
Story
A crowded concert has a velvet rope. Fans with the right wristband stroll through a special side door, but nobody pays energy to go downhill.
Connect the pieces
- F (Fluffy) → Facilitated: Substances move down their concentration gradient with help from membrane proteins, without ATP.
- G (Goats) → Gradient: Facilitated diffusion still requires a concentration gradient.
- S (Snore) → Saturable: Transport proteins can become occupied, so the process is specific and saturable.
- Fluffy · Facilitated: Substances move down their concentration gradient with help from membrane proteins, without ATP.
- Goats · Gradient: Facilitated diffusion still requires a concentration gradient.
- Snore · Saturable: Transport proteins can become occupied, so the process is specific and saturable.
Know the limits
It still requires a concentration gradient; if movement is against the gradient, a different transport mechanism is needed.
Further reading · OpenStax science and mathematics textbooks ↗Check your understanding
Which statement best describes facilitated diffusion?
A. Directly changes a molecule’s chemical structure
B. Requires ATP to move solute against a gradient
C. Uses a protein to move substances down a gradient
D. Moves water only through the membrane lipids
Reveal explanation
Uses a protein to move substances down a gradient
Facilitated diffusion relies on membrane proteins but does not require energy because movement is down the gradient.