Transpiration & Potometer Experiment
Investigate how light, temperature, humidity and air movement affect plant water loss and observe water uptake using a virtual potometer.
Potometer bubble movement represents relative water uptake.
Choose environmental conditions and press Run Experiment.
🎯 Aim
To investigate the effects of light intensity, temperature, humidity and air movement on plant transpiration and relative water uptake.
🧰 Virtual Apparatus
Leafy shoot/plant model, capillary potometer, water reservoir, air bubble marker, light source, fan and environmental controls.
📘 Theory
Transpiration is the loss of water vapour from the aerial parts of a plant, particularly through stomata in leaves.
Water lost from leaves contributes to a water-potential gradient that supports water movement through the xylem.
🌿 Factors Affecting Transpiration
Light
In many plants, stomata tend to be more open in light to support gas exchange for photosynthesis, which can increase transpiration.
Temperature
Higher temperature can increase evaporation and diffusion of water vapour, increasing transpiration when water is available.
Humidity
High external humidity reduces the water-vapour gradient between the leaf and surrounding air, generally reducing transpiration.
Air Movement
Moving air can remove humid air near leaf surfaces and maintain a steeper water-vapour gradient, often increasing transpiration.
📏 How the Potometer Works
A cut leafy shoot in a real potometer is connected to a water-filled capillary system. As the shoot takes up water, an introduced air bubble can move along the calibrated tube. The distance moved over a known time can be used to estimate relative water uptake.
Relative water uptake rate = Bubble distance moved ÷ Time
A real quantitative potometer can use capillary cross-sectional area to estimate the volume of water taken up.
📋 Observation Table
| Trial | Light | Temperature | Humidity | Air Movement | Condition | Bubble Distance | Relative Rate |
|---|---|---|---|---|---|---|---|
| Run an experiment and press Record. | |||||||
⚖️ Fair-Test Investigation
Change only one environmental variable at a time while keeping the other conditions constant.
📝 Procedure
- Begin with Medium light, 25°C, Medium humidity and Still air.
- Press Run Experiment.
- Observe water movement through the xylem.
- Observe simulated water-vapour loss from the leaves.
- Measure the virtual air-bubble movement.
- Press Record.
- Increase light intensity and repeat.
- Investigate temperature while keeping other variables constant.
- Investigate low, medium and high humidity.
- Investigate still, medium and high air movement.
- Compare Light and Dark conditions.
🧠 Prediction Challenge
🎓 Quick Viva
1. What is transpiration?
Transpiration is the loss of water vapour from the aerial parts of plants, especially through leaf stomata.
2. What does a potometer directly measure?
A potometer measures water uptake by a shoot. It does not directly measure water loss from the leaves.
3. Why does high humidity usually reduce transpiration?
It reduces the difference in water-vapour concentration between the moist leaf air spaces and the surrounding atmosphere.
4. Why can wind increase transpiration?
Moving air removes humid air near the leaf surface, helping maintain a water-vapour gradient.
5. Which tissue transports water through a plant?
Xylem transports water and dissolved mineral ions from roots toward aerial tissues.
6. What are stomata?
Stomata are microscopic pores in the epidermis of leaves and some stems. Guard cells regulate their opening.
7. Why may darkness reduce transpiration in many plants?
Stomata of many species tend to close more in darkness, which reduces stomatal water loss. This response is not identical in every plant species.
✅ Result
The simulation demonstrates that environmental conditions can change plant transpiration and water uptake. Greater light, warmer conditions and increased air movement can increase transpiration under suitable conditions, while high humidity generally reduces it. Potometer bubble movement provides an indirect estimate of water uptake rather than a direct measurement of transpiration.