Question

a carrier protein is required for ________.
a simple diffusion
b facilitated diffusion and active transport
c osmosis
d simple diffusion and osmosis

Explanation:

• Option A: Simple diffusion is the movement of molecules from an area of high concentration to low concentration without the need for a carrier protein or energy. So A is incorrect.
• Option B: Facilitated diffusion requires a carrier protein (or channel protein) to help molecules move across the membrane down their concentration gradient. Active transport also requires carrier proteins to move molecules against their concentration gradient, using energy. So B is correct.
• Option C: Osmosis is the diffusion of water across a selectively permeable membrane, and it does not require a carrier protein (water can move through aquaporins, but osmosis as a process of water movement down its water potential gradient doesn't strictly require carrier proteins in the same way as facilitated diffusion/active transport for solutes). So C is incorrect.
• Option D: As explained, simple diffusion and osmosis do not require carrier proteins, so D is incorrect.

Answer:

B. facilitated diffusion and active transport