Diffusion and Osmosis

In this laboratory the students will investigate the processes of diffusion and osmosis in a model of a membrane system. They will also investigate the effect of solute concentration on water potential as it relates to living plant tissues.

Cells have particular structures that underlie their functions. Every cell is surrounded by a membrane that separates it from the outside world. Inside the cell is a concentrated mixture of thousands of different molecules which form a variety of specialized structures that carry out such cell functions as energy production, transport of molecules, waste disposal, synthesis of new molecules, and the storage of genetic material.

A basic understanding of diffusion and osmosis concepts is required.

This laboratory suggests that parts 1B and 1C be completed by all students. I have found that having all groups perform each sucrose dilution becomes quite cumbersome and time consuming. Most of us do not have this much equipment for several groups of students. I have assigned a concentration to each group and they use that concentration for both 1B and 1C. They then share their data with each other.

NA

If graphing calculators are available but the CBL equipment is not, students could enter their collected data into the graphing calculator and perform a linear regression. On part 1C the students could figure the water potential as in the laboratory activity included in this unit but enter their data into the spreadsheet directly.

If both graphing calculators and a CBL interface are available, substitute the Water Potential in Potato Cells-Osmotic Pressure for part 1C. This works well and I think a better understanding of water potential is gained by the students.

None required but if computers are available, a graphing analysis program could be used to analyze the data.