Which of the following is an example of osmosis?

• A. Oxygen diffusing from the lungs into the bloodstream
• B. Sodium ions moving through a channel protein down their concentration gradient
• C. Glucose being transported into a cell via active transport
• D. Water moving from a region of low solute concentration to high solute concentration across a selectively permeable membrane

Answer: (D)

Verified step by step guidance

1. Understand the concept of osmosis: Osmosis is the movement of water molecules across a selectively permeable membrane from a region of low solute concentration to a region of high solute concentration. This process does not require energy and occurs due to the concentration gradient of solutes.
2. Analyze the options provided: Oxygen diffusing into the bloodstream is an example of simple diffusion, not osmosis. Sodium ions moving through a channel protein is facilitated diffusion, and glucose being transported via active transport requires energy, which is not osmosis.
3. Focus on the correct example: Water moving from a region of low solute concentration to high solute concentration across a selectively permeable membrane fits the definition of osmosis.
4. Relate the process to biological systems: In cells, osmosis often occurs across the plasma membrane, where water moves to balance solute concentrations inside and outside the cell.
5. Conclude the reasoning: The correct answer is the example involving water movement across a selectively permeable membrane, as it aligns with the definition of osmosis.