Question

question 19 of 32
facilitated diffusion is a type of passive transport that allows solutes to move across the plasma membrane of a cell.
which statements describe facilitated diffusion?

• small, charged molecules and ions move down their concentration gradient into a cell through proteins in the plasma membrane.
• membrane proteins do not use energy to move solutes across the membrane down their concentration gradient.
• solutes move down their concentration gradient directly through the plasma membrane without the use of energy.
• solutes move across the membrane against their concentration gradient through specialized membrane proteins.
• small, uncharged molecules move down their concentration gradient into a cell directly through the plasma membrane.

Explanation:

Facilitated diffusion is passive transport (no energy use) where solutes move down concentration gradients via membrane proteins. Small charged molecules/ions rely on these proteins (they can’t cross the lipid bilayer directly). The first statement correctly identifies the role of proteins for charged solutes moving down gradients. The second statement aligns with passive transport (no energy expenditure by proteins). Other options are incorrect: direct movement through the membrane (third/fifth) describes simple diffusion, and moving against gradients (fourth) is active transport.

Answer:

Small, charged molecules and ions move down their concentration gradient into a cell through proteins in the plasma membrane.
Membrane proteins do not use energy to move solutes across the membrane down their concentration gradient.