Question

the majority of water molecules moving across plasma membranes by osmosis do so via a process that is most similar to ____.

○ cotransport
○ active transport
○ facilitated diffusion
○ a process that requires energy from the cell
○ simple diffusion

Explanation:

1. Recall the mechanisms of water movement across plasma membranes: Most water moves via aquaporins (channel proteins), which is a type of facilitated diffusion (passive, uses channels to move down concentration gradient).
2. Analyze options:

• Cotransport: Involves moving two substances, often against gradients with energy from one's down - gradient movement, not like water's osmosis - related movement.
• Active transport: Requires energy (ATP), but water movement via osmosis (majority via aquaporins) is passive, so this is incorrect.
• Facilitated diffusion: Passive transport using channels (aquaporins for water), matches water's movement (down concentration gradient, via protein channels).
• “A process that requires energy...” is wrong as water movement is passive.
• Simple diffusion: Water can do simple diffusion, but majority is via facilitated diffusion (aquaporins), so facilitated diffusion is more similar.

Answer:

C. facilitated diffusion