Water moves across biological membranes towards:

Question

BlackTom AI · Accepted Answer

Water moves from regions of higher water potential to regions of lower water potential — equivalently, from lower solute concentration toward higher solute concentration (osmosis).

1) Relevant knowledge points and concepts
- Osmosis is the passive diffusion of water across a semipermeable membrane.  
- Water potential (or free water) is reduced by solutes; the side with more solute has lower water potential.  
- Water therefore moves toward the side with higher solute concentration (hypertonic side) until equilibrium (or pressure balance) is reached.

2) Step-by-step reasoning
- Consider two compartments separated by a membrane: one with lower solute concentration (more free water) and one with higher solute concentration (less free water).  
- Because of the water potential difference, there is a net flux of water molecules from the dilute side into the concentrated side.  
- This movement equalizes chemical potential of water, not solute movement (solute may be impermeable).

3) Illustrative calculation (intermediate steps)
- Use van ’t Hoff’s approximation for osmotic pressure π ≈ cRT to show driving force. Let R = 0.08206 L·atm·K−1·mol−1 and T = 298 K.
- If compartment A has cA = 0.10 M: πA = 0.10 × 0.08206 × 298 ≈ 2.45 atm.
- If compartment B has cB = 0.40 M: πB = 0.40 × 0.08206 × 298 ≈ 9.78 atm.
- Δπ = πB − πA ≈ 7.33 atm, so water is driven from A to B (toward the higher solute concentration).

4) Why the correct answer is correct
- The phrase “more concentrated solutes” captures the general principle: water moves toward the side with greater solute concentration (lower water potential). This is the definitionally correct direction for osmosis.

5) Why the other options are incorrect
- “Less concentrated solutes” is the opposite of osmosis direction (water moves away from this side).  
- “More concentrated potassium” and “less concentrated potassium” single out a particular ion; osmosis depends on overall solute concentration and impermeability, not the identity of the solute. While “more concentrated potassium” would technically attract water if it increases total solute concentration, the best general and correct choice is “more concentrated solutes.”

6) Conclusion
This reasoning confirms the correct answer: more concentrated solutes.

Water moves across biological membranes towards:单项选择题

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