Diffusion / Osmosis Apparatus

Product Code: ME-6940


It is an image that appears in practically every biology text to help students with conceptual understanding:  a U-shaped tube with a permeable membrane separating a hypotonic and hypertonic solution.  And yet most classroom methods of studying osmosis don’t take advantage of the simplicity and elegance of this design for actual lab work.

But the PASCO Diffusion/Osmosis apparatus has other distinct advantages.  It actually allows students to explore the rate of water movement and quantify pressure changes occurring in the system.  And it does it all accurately and in a fraction of the time of using a dialysis bag.

And because of the versatility of its design, the Diffusion/Osmosis Apparatus can be used with beginning biology students simply to show the movement of water due to osmosis or to illustrate the concept of semi-permeability while advanced students can measure the effects of varying the solute concentrations or changing the pressure of the two solutions.

This versatility also means the same setup can be used by chemistry teachers exploring relationships between volume and pressure or environmental science teachers wishing to illustrate water movement in soil and within a plant.


  • The U-shaped design provides familiarity for students and the straight columns keep the volume of gas above the fluid constant.
  • Graduated transparent columns allow changes in volume to be seen and quantified
  • Membranes are quick andeasy to replace when compromised
  • Air tight joints prevent pressure leaks
  • Free standing unit requires no additional lab equipment to hold it in place
  • Plastic rather than glass columns for durability and student safety

Product Specifications

Membrane Pore Size 40–50 μm
Membrane Molecular Weight Cut-Off 6,000 daltons
Membrane Temperature Range 4–60 °C
Membrane pH Range 2–12

How It Works

The Diffusion/Osmosis Apparatus is a U-shaped tube composed of two columns separated by a semi-permeable membrane. Alone, the Diffusion/Osmosis Apparatus allows students to observe and measure volume changes due to osmosis and solute changes due to diffusion. With the PASPORT Dual Pressure Sensor (sold separately), the Diffusion/Osmosis Apparatus allows students to measure the changes in pressure and volume caused by the osmotic movement of water across a semi-permeable membrane from a hypotonic solution to a hypertonic solution.

What’s Included

  • 1x Diffusion Osmosis Apparatus
  • 2x Leur connectors (for use with the Wireless Pressure Sensor)

Recommended Accessories

PASPORT Dual Pressure Sensor PS-2181

Replacement Parts

Replacement Osmosis Membranes ME-6941

Support Documents

Manual Downloads

Product Manuals for the Diffusion/Osmosis Apparatus (ME-6940)


Replacement Membranes

Replacement membranes for use with the Diffusion/Osmosis Apparatus (ME-6940)