Question

if a solute is moving through a phospholipid bilayer from an area of higher concentration to an area of lower concentration without the assistance of a protein, the manner of transport must be ______.
○ solutes cannot cross phospholipid bilayers
● simple diffusion
○ solutes may use active transport, facilitated diffusion, or simple diffusion, depending on the solute.
○ facilitated diffusion
○ active transport

Explanation:

To determine the correct answer, we analyze each option:

• "Solutes cannot cross phospholipid bilayers": Incorrect, as some solutes (like small non - polar molecules) can cross.
• "Simple diffusion": Simple diffusion is the movement of solutes from high to low concentration across a membrane without the help of proteins. This matches the description in the question.
• "Solutes may use active transport, facilitated diffusion, or simple diffusion, depending on the solute": The question specifies no protein assistance, so active transport (needs energy and often proteins) and facilitated diffusion (needs protein channels/carriers) are ruled out. So this option is incorrect.
• "Facilitated diffusion": Requires protein assistance, which is not present here, so incorrect.
• "Active transport": Requires energy and usually protein transporters, and moves against concentration gradient (low to high), so incorrect.

Answer:

B. simple diffusion (assuming the option with "simple diffusion" is labeled as B, if the original labeling was different, adjust the label accordingly. Based on the given options, the correct one is the "simple diffusion" option)