How does osmosis differ from diffusion

Diffusion occurs when molecules spread out to fill available space, moving down their concentration gradient until equilibrium is reached. It does not require a membrane, although a membrane can slow the rate if it is present. Examples include oxygen entering cells and carbon dioxide leaving them, both driven solely by differences in gas concentration.

Key Differences Between Osmosis and Diffusion

Four fundamental contrasts:

• Substance moved: water for osmosis, any solute for diffusion.
• Direction: water moves toward higher solute concentration; solutes move toward lower concentration.
• Membrane requirement: osmosis needs a selectively permeable membrane; diffusion can occur without one.
• Driving force: water potential gradient for osmosis; concentration gradient for diffusion.

Osmosis depends on water potential, which combines solute concentration and pressure. Consider a beaker with pure water (0 M) separated by a semipermeable membrane from a 0.5 M glucose solution. The water potential of the glucose side is lower, so water flows into it. After 10 minutes, the volume on the glucose side increases by about 2 mL, illustrating how a simple concentration difference can generate measurable water movement.

To observe osmosis in the lab:

1. 1Place a dialysis bag filled with 0.2 M NaCl solution in a beaker of distilled water.
2. 2Mark the water level inside the bag.
3. 3After 15 minutes, measure the new water level; it will be higher, showing water entered the bag.

Comparison of properties: