The Best Osmosis and Diffusion Lab for High School Biology

The Best Osmosis and Diffusion Lab for High School Biology: Engaging, Visual, and Data-Driven

Looking for the perfect biology lab to teach osmosis and diffusion?
This hands-on lab activity combines visual learning with measurable results. And, best of all, it’s easy to set up, uses common lab materials, and reinforces essential biology concepts like plasmolysis, hypotonic vs. hypertonic solutions, active vs. passive transport, and water movement across cell membranes.

✅ Minimal prep
✅ Simple materials
✅ Microscopy, graphing, and calculations—all in one lab!

Why Every Biology Teacher Needs This Osmosis and Diffusion Lab:

When it comes to teaching cell transport processes like osmosis, diffusion, and plasmolysis, it’s critical to move beyond definitions and diagrams. Students need to see it. They need to measure it. They need to analyze it.

That’s why this osmosis and diffusion lab activity has become a staple in my high school biology classroom. It checks every box:

• Reinforces microscope skills
• Visualizes plasmolysis in plant cells
• Engages students in weighing, measuring, and calculating
• Requires a hand-drawn graph
• Promotes data analysis and critical thinking
• Illustrates real-world application of scientific method

A Timeless Biology Lab That Just Works

Osmosis and diffusion are cornerstones of any cell structure and function unit. While there are many labs available on this topic, this one stands out. I’ve used countless variations over the years, and this two-part lab consistently generates the strongest student engagement and understanding.

When students literally say, “Whoa, that’s so cool!” as they watch plasmolysis unfold under the microscope—that’s a teaching win.

Part A: Observing Plasmolysis in Real Time (Qualitative)

In the first part of the lab, students observe osmosis in plant cells using a microscope. Start with a thin layer of red onion skin or a leaf from an Elodea (Anacharis) plant. Students first examine the cells in distilled water, sketch the cells, and note the position of the cytoplasm and vacuole.

Next comes the wow moment: swap the distilled water for a 15% salt solution. The plasmolysis is immediate and dramatic. Students watch as the cell membrane pulls away from the cell wall due to water loss. It’s the perfect visual demonstration of hypertonic solutions in action.

Part B: Measuring Osmosis in Potato Cores (Quantitative)

The second half of the lab brings in data analysis and graphing practice—making it ideal for reinforcing both science content and scientific skills.

Here’s how it works:

1.     Use a cork borer to create uniform potato cores.

2.     Mass the cores in groups of four and record the initial weight.

3.     Place each group in a different sucrose solution of known molarity.

4.     Let them sit overnight.

5.     Re-mass the cores the next day and calculate the percent change in mass.

6.     Plot the data to determine the solute concentration of the potato tissue.

7.     Analyze whether each solution was hypotonic, hypertonic, or isotonic.

The beauty of this activity? It reinforces the concepts of osmotic pressure, solute concentration, and equilibrium, all while helping students master graphing and data interpretation.

Looking for a ready-to-use resource that includes  student instructions, answer keys, and editable versions? Check out my Osmosis and Diffusion Lab on Teachers Pay Teachers! It's classroom-tested, student-approved, and designed to make your job easier.