Multiple Choice
In the context of passive transport across a selectively permeable membrane, what is the diffusion of water called?
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9. Transport Across Membranes
Passive Transport: Diffusion and Osmosis
Multiple Choice
During osmosis across a selectively permeable membrane, which molecule does NOT move across the membrane (assuming only water can pass)?
A
Water molecules
B
Aquaporin channel proteins
C
Solute molecules (e.g., Na and Cl)
D
Phospholipid molecules in the membrane bilayer
Verified step by step guidance1
Understand the process of osmosis: Osmosis is the movement of water molecules across a selectively permeable membrane from an area of lower solute concentration to an area of higher solute concentration.
Identify which molecules can move during osmosis: Water molecules can move freely through the membrane, often facilitated by aquaporin channel proteins that specifically allow water passage.
Recognize the role of solute molecules: Solute molecules such as Na\+ and Cl\- are generally unable to pass through the selectively permeable membrane during osmosis because the membrane restricts their movement to maintain concentration gradients.
Consider the membrane structure: Phospholipid molecules form the bilayer of the membrane and do not move across it; they are structural components rather than transported molecules.
Conclude that during osmosis, the molecules that do NOT move across the membrane are the solute molecules, as only water is allowed to pass through the membrane channels.
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