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AP Biology Practice Quiz: Facilitated Diffusion

Written by AP Content Team, Verified for 2026 AP Exams, Last updated: May 2026

Test your understanding with short quizzes. This quiz has 10 questions to check your progress.

Question 1 of 10

According to the provided text, which of the following is a key characteristic of facilitated diffusion?

All Questions (10)

According to the provided text, which of the following is a key characteristic of facilitated diffusion?

A) It requires metabolic energy in the form of ATP.

B) It moves substances against their concentration gradient.

C) It allows movement down a concentration gradient without energy input.

D) It is a non-specific process that allows any molecule to pass through the membrane.

Correct Answer: C

The content explicitly states that facilitated diffusion allows large polar molecules to move 'down their concentration gradient through membranes without energy input'.

Based on the information provided, which type of molecule would most likely require a channel or transport protein to cross the plasma membrane?

A) A small, nonpolar molecule

B) A charged sodium ion (Na+)

C) A lipid-soluble hormone

D) A small gas molecule like oxygen

Correct Answer: B

The text specifies that 'facilitated diffusion requires channel or transport proteins for charged ions like Na+ and K+ to move through the membrane'. The charge of the ion prevents it from easily passing through the nonpolar lipid bilayer.

What is the specific function of aquaporins as described in the text?

A) To transport Na+ and K+ ions, leading to membrane polarization.

B) To move large polar molecules against their concentration gradient.

C) To facilitate the transport of large quantities of water across membranes.

D) To allow any large molecule to pass through the membrane without energy.

Correct Answer: C

The content directly defines aquaporins as 'specific channel proteins that facilitate the transport of large quantities of water across membranes'.

The movement of charged ions such as Na+ and K+ through their respective channel proteins can directly contribute to which of the following cellular conditions?

A) The synthesis of proteins

B) The passive transport of lipids

C) Membrane polarization

D) The breakdown of the plasma membrane

Correct Answer: C

The text states that the movement of charged ions like Na+ and K+ through channel proteins 'can lead to membrane polarization'.

Facilitated diffusion is a necessary process for molecules whose structure prevents them from easily crossing the plasma membrane. This process is required for which of the following?

A) Small nonpolar molecules and lipids

B) All molecules moving against a gradient

C) Large polar molecules and charged ions

D) Only water molecules

Correct Answer: C

The content specifies that facilitated diffusion is used for 'charged ions like Na+ and K+' and 'large polar molecules', both of which cannot easily pass through the lipid bilayer due to their structure.

A cell needs to rapidly absorb a large volume of water from its environment. This process is most efficiently accomplished through which mechanism described?

A) The use of transport proteins for large polar molecules.

B) The movement of Na+ and K+ ions to create a charge differential.

C) The action of aquaporins, which are specific water channels.

D) An energy-dependent process to pump water into the cell.

Correct Answer: C

The text identifies aquaporins as 'specific channel proteins that facilitate the transport of large quantities of water across membranes,' which directly addresses the need for rapid, large-volume water transport.

A fundamental principle mentioned is that a molecule's structure affects its ability to pass through the plasma membrane. How does facilitated diffusion address this for certain molecules?

A) It changes the structure of the molecule to make it nonpolar.

B) It provides a protein-based pathway to bypass the lipid bilayer.

C) It uses energy to force polar molecules through the lipid core.

D) It dissolves the membrane temporarily to allow passage.

Correct Answer: B

For molecules whose structure (e.g., being large, polar, or charged) prevents passage through the lipid bilayer, facilitated diffusion utilizes channel or transport proteins to provide an alternative pathway across the membrane.

A researcher discovers that the transport of a specific large polar molecule into a cell stops when a substance that blocks protein channels is added. The molecule continues to be more concentrated outside the cell. What type of transport was likely occurring?

A) Simple diffusion, because no energy was used.

B) Active transport, because a protein was blocked.

C) Facilitated diffusion, because it involves protein channels and movement down a gradient.

D) Water transport via aquaporins, because it is a polar molecule.

Correct Answer: C

The scenario describes the movement of a large polar molecule down its concentration gradient, which is dependent on a protein. This matches the description of facilitated diffusion, which uses channel or transport proteins and does not require energy.

A genetic disorder causes the channel proteins for K+ ions to be non-functional. Based on the provided text, which of the following would be an immediate consequence for a cell with this disorder?

A) The cell could no longer transport large quantities of water.

B) The cell would be unable to move K+ ions across the membrane via facilitated diffusion.

C) The cell would expend more energy to transport large polar molecules.

D) The structure of the plasma membrane would be compromised.

Correct Answer: B

The text states that charged ions like K+ require channel proteins for facilitated diffusion. If these specific proteins are non-functional, the facilitated movement of K+ ions down their concentration gradient would be impaired or prevented.

Which statement best synthesizes the information about the transport of water and the transport of Na+ ions?

A) Both are forms of facilitated diffusion that utilize specific, distinct channel proteins.

B) Both processes require energy and result in membrane polarization.

C) Water moves through Na+ channels, while Na+ moves through aquaporins.

D) Both are large polar molecules that move against their concentration gradient.

Correct Answer: A

The text describes both processes as facilitated diffusion. It specifies that Na+ uses channel proteins and that water uses specific channel proteins called aquaporins. This indicates that both use specific protein channels to move down their respective gradients.