Plant Transpiration Experiment for Biology Students (Easy Lab Activity)

This plant transpiration experiment allows students to measure water loss from leaves while testing environmental variables such as light, air movement, and humidity. This hands-on biology lab helps students understand how transpiration works and how external conditions affect the rate of water loss in plants. Because the setup is simple and reliable, this transpiration experiment works well for middle school and high school biology students.

Plant Transpiration Activity for Biology Students

I really enjoy teaching plant biology, and plant transpiration is one of those topics that becomes much more meaningful when students can actually see it happening. I recently used this simple plant transpiration activity with my biology students, and it was easy to set up, required no fancy lab equipment, and worked beautifully across multiple grade levels. This transpiration activity can be adapted for elementary, middle school, or high school biology classrooms, making it a flexible option for teaching plant water movement.

Looking for a fully developed, classroom-ready transpiration lab for high school biology? You can find my updated transpiration lab activity blog post here.

What Is Plant Transpiration?

Plant transpiration is the loss of water vapor from a plant’s leaves. Leaves contain small pores called stomata that open to allow carbon dioxide to enter for photosynthesis. While the stomata are open, water vapor also escapes from the leaf and enters the atmosphere. If a plant loses too much water through transpiration, it will lose turgor pressure, causing the plant to wilt.

Because transpiration is closely tied to photosynthesis, environmental conditions such as light, air movement, and humidity all affect the rate at which water is lost from the leaves.

Simple Plant Transpiration Activity Setup

Measuring transpiration from plant leaves can be surprisingly simple. For this activity, I purchased a tray of vinca plants (also called periwinkles) from a local garden center. One tray typically contains six small plants, which works well for testing multiple conditions.

Each plant was placed into a small 100 mL beaker and watered thoroughly. Since the goal is to measure water lost through the leaves, it is important to prevent evaporation from the soil. To do this, a plastic sandwich bag is wrapped tightly around the beaker and sealed snugly around the stem of the plant. Only the leaves should remain outside the bag.

At this point, the only way water can leave the system is through the leaves of the plant.

Measuring Transpiration by Mass

Once the setup is complete:

1. Place the plant into the beaker and water it thoroughly.

2. Wrap the plastic bag tightly around the beaker and stem so no soil is exposed.

3. Measure the initial mass of the entire setup and record it on masking tape attached to the beaker.

This initial mass serves as the baseline for measuring water loss during transpiration.

Testing Variables That Affect Transpiration

Next, students investigate which environmental factors increase or decrease the rate of transpiration. In this activity, four plants are used:

• One plant is placed under continuous light.

• One plant is placed in front of a blowing fan.

• One plant is sealed inside a plastic bag that has been lightly misted with water to create a high-humidity environment.

• One plant serves as the control and remains under normal classroom conditions.

Each plant is left in its assigned condition for approximately 24 hours.

Observing and Analyzing Results

After 24 hours, each plant is massed again. Students are often amazed by how much water has been lost through the leaves during this time.

Typical results include:

• Plant in continuous light: Increased transpiration due to sustained photosynthesis. Stomata remain open longer to allow carbon dioxide to enter, resulting in greater water loss.

• Plant in front of a fan: Increased air movement removes water vapor from the leaf surface, increasing evaporation and transpiration.

• High-humidity plant: Reduced transpiration because the surrounding air already contains a high concentration of water vapor.

• Control plant: Normal transpiration under standard room conditions.

  

All final masses should be compared to the control plant to determine whether the tested factor increased or decreased the rate of transpiration.

Adapting This Transpiration Activity for Different Grade Levels

One of the strengths of this activity is its flexibility.

Elementary Grades:
At the elementary level, this activity can be used to demonstrate that water is absorbed by roots and released through leaves. Students can make predictions, form simple hypotheses, and practice basic steps of the scientific method.

Middle Grades:
Middle school students can calculate the rate of water loss per minute, test additional variables such as darkness or temperature, or compare transpiration rates between different plant species.

High School Biology:
High school students can remove leaves and calculate total leaf surface area to determine water loss per unit area. Students may also research and connect results to mechanisms of transpiration, including cohesion, adhesion, capillary action, and transpiration pull.

Final Thoughts

This simple plant transpiration activity allows the same core concept to be explored at multiple levels of complexity. Many students have limited experience working with live plants, and labs like this one consistently spark curiosity and engagement. My students are always intrigued by how much water plants actually lose through their leaves.

If you try this activity in your classroom or have additional ideas for extensions, I would love to hear about it. Good luck — and as always, make science fun.