Question

which of the following statements regarding carrier - mediated facilitated diffusion is false?
the carrier protein has two configurations, one open to the outside, one open to the cytoplasm.
the carrier protein moves solute molecules against a concentration gradient.
the carrier protein moves hydrophilic molecules through a membrane.
the carrier protein is an intrinsic membrane protein.

Explanation:

1. Recall the concept of carrier - mediated facilitated diffusion:

• Carrier - mediated facilitated diffusion is a type of passive transport. Passive transport moves substances down their concentration gradient (from an area of high concentration to an area of low concentration) and does not require energy input.
• Analyze each option:
• Option 1: Carrier proteins do have two conformations, one open to the extracellular space and one open to the cytoplasm, so this statement is true.
• Option 2: Moving solute molecules against a concentration gradient is active transport, not facilitated diffusion. Facilitated diffusion (including carrier - mediated) moves substances down the concentration gradient. So this statement is false.
• Option 3: Carrier proteins help hydrophilic molecules (which cannot pass through the lipid - bilayer of the membrane easily) to cross the membrane, so this statement is true.
• Option 4: Carrier proteins are intrinsic (integral) membrane proteins as they span the lipid bilayer, so this statement is true.

Answer:

B. The carrier protein moves solute molecules against a concentration gradient.