Subject Area

 Membrane Transport
Age or Grade

 10th/11th grade Biology
Estimated Length

2 class blocks (~2.5 hrs)
Prerequisite knowledge/skills

 Students should have a basic understanding of cell structure and biological molecules. They should also be  familiar with the concept of solute, solvents and concentration.
Description of New Content

 Definition of active and passive transport and relating it to real-life examples.
Demo and lab activities to help students experience diffusion and osmosis first-hand.

  • Understand the functional role of the cell membrane in cell survival.
  • Understand the basic mechanisms by which biological molecules and water are transported within a living organism.
  • Appreciate how cells maintain homeostasis through osmosis and why it is important.
  • Relate the concepts of osmosis and diffusion to the requirements of plant and animal cells;
Materials Needed

Diffusion demo: beaker, water, food coloring, hot plate
Osmosis lab: potato slices, salt, distilled water, centrifuge tubes, mass balance






a. Engage - Discuss with the class the necessity for the cell membrane as a physical barrier protecting the contents of the cell.  The selective permeability of the cell should be emphasized.

b. Demo - Students explore the  diffusion through a simple demo. Students will write down their observations as the teacher adds a drop of food coloring to a beaker of water. This demo is repeated in cold water and hot water to study the effect of temperature on the process of diffusion. Students are asked to write down and share other examples of diffusion experienced in everyday life.  


a. Pre-lab - Students explore the effect of different concentrations of salt solution on Elodea cells under the microscope (Slides are prepared in advance).  Students are encouraged to sketch the cells and make observations on their appearance. The post-activity discussion should focus on the student's explanations of the changes they observed.

b. Lab activity - Students  work in groups of 2-3 to design and test their own hypothesis regarding the effects of various salt solutions on the mass and appearance of potato slices. Review the Elodea activity if necessary. 

Download Osmosis Lab - Powerpoint or PDF


As a post-laboratory exercise, discuss mechanisms by which cells and our body counter the effects of unfavorable osmotic environments.


a. Students will be assessed on their ability to formulate a good hypothesis and procedure for the lab. They will also tabulate the collected data and be graded on their understanding and conclusions.
b. Students will also be given a quiz to assess their understanding of the concepts and vocabulary.

If time permits, do another lab activity with a selectively permeable dialysis membrane. (see reference)
References Optional osmosis lab activity on the web: - http://biology.arizona.edu/sciconn/lessons/mccandless/osmosis.html 
Contemporary Biology: Exploring the Science of Life (Textbook)