Featured in PASCO’s College Biology Instructor Guide

College Biology Instructor Guide


College Instructor edition with 26 experiments covering introductory and general biology topics.

Diffusion and Osmosis

Lab Summary

Use a water quality sensor to measure the changes in conductivity in two solutions separated by a semi permeable membrane.


The concept of transport across membranes is fundamental to understanding cell structure and function. In this lab, students investigate diffusion, osmosis, and facilitated diffusion using artificial membranes, tissue cores, and individual cells. Students:

  • Investigate the processes of diffusion and osmosis in model membrane systems.
  • Investigate the processes of osmosis in living plant tissue, and relate solute concentration to water potential.
  • Use light microscopy to observe osmosis in living cells.
  • Understand the concepts of diffusion and osmosis, and why they are important for understanding cell structure and function.
  • Observe the effects of solute size and concentration gradients on diffusion across a semipermeable membrane.



  • Sample Lab - Diffusion and Osmosis (911 KB – PDF)
  • Method

    By performing this laboratory, students should be able to:

    • Use a conductivity sensor to determine the relative size of water molecules, solutes, and membrane pores.
    • Conceptualize molarity/solute concentration, and how it relates to osmotic potential of a solution.
    • Use experimental evidence to determine the sucrose concentration of unknown solutions.
    • Set up a controlled experiment to calculate the water potential of cells.
    • Understand the importance of water potential, and how it relates to solute concentration and pressure potential within a cell.
    • Use basic light microscopy skills to observe the effects of the movement of water into and out of plant cells.
    • Understand the following concepts: tonicity, plasmolysis, crenation, tugor, and cell lysis.

    Sensors / Equipment Used:

    PASPORT Water Quality Sensor


    Measures temperature, conductivity, pH/ISE/ORP and dissolved oxygen. It is specifically designed for convenience in conducting water quality lab experiments. For use with PASPORT Interfaces.

    Materials Used:

    1% starch solution - - 30 mL
    15% NaCl solution 2 to 3 drops
    2% IKI solution - 150 mL
    2% IKI/2% NaCl solution - 150 mL
    Beaker or cups, 30-mL - 6
    Beaker, 250-mL - 2
    Cork borer 
    Cover slip 
    Dental floss or string - 10 to 20 cm
    Dialysis tubing - 180 cm
    Disposable pipet - 5
    Distilled water - 1 liter
    Electronic Balance - 1 per class
    Graduated cylinder, 25-mL 
    Knife - 1 per class
    Labeling marker and tape 
    Microscope slide 
    Potato - 3 to 4 per class
    Red Onion - 1 per class
    Roll of paper towels - 1 per class
    Roll of plastic wrap - 1 per class
    Small funnel 
    Sucrose solutions (0.2 M, 0.4 M, 0.6 M, 0.8 M and 1.0 M) - 35 mL each
    Wash bottle 

    The Associated Bundle:

    College Biology Bundle


    A complete probeware bundle designed for PASCO's College Biology curriculum

    Interface Required

    This experiment may require software and an interface for data collection.