AP Biology Flashcards: Facilitated Diffusion
Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026
Review key ideas with interactive flashcards. This set includes 10 cards to help you master important concepts.
What are aquaporins?
Aquaporins are specific channel proteins that facilitate the rapid transport of large quantities of water across cell membranes.
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What are aquaporins?
Aquaporins are specific channel proteins that facilitate the rapid transport of large quantities of water across cell membranes.
What is facilitated diffusion?
Facilitated diffusion is the passive movement of large polar molecules or charged ions down their concentration gradient through a membrane using a channel or transport protein.
How does a molecule's structure, such as being large and polar, affect its ability to pass through the plasma membrane?
A large, polar structure prevents a molecule from easily passing through the nonpolar lipid bilayer, necessitating a mechanism like facilitated diffusion.
What is the role of channel proteins in facilitated diffusion?
Channel proteins provide a specific pathway for charged ions or large polar molecules to move through the otherwise impermeable plasma membrane.
What types of molecules require facilitated diffusion?
Large polar molecules and charged ions, such as Na+ and K+, require facilitated diffusion to pass through the plasma membrane.
What is a potential consequence of moving charged ions like Na+ and K+ across the membrane via facilitated diffusion?
The movement of charged ions through channel proteins can lead to membrane polarization, which is a difference in electrical charge across the membrane.
What is the driving force for the movement of substances in facilitated diffusion?
The driving force is the concentration gradient, which causes substances to move from an area of higher concentration to an area of lower concentration without energy.
How would a sodium ion (Na+) cross the plasma membrane to move down its concentration gradient?
A sodium ion would move through a specific channel or transport protein via facilitated diffusion, as it is a charged particle.
Does facilitated diffusion require energy input?
No, facilitated diffusion does not require energy input because substances move down their concentration gradient.
A cell needs to rapidly absorb a large volume of water. What specific transport mechanism and protein would be used?
The cell would use facilitated diffusion involving aquaporins, which are channel proteins specialized for transporting water.