Overview
This lecture focuses on measuring the rate of water loss (transpiration) in coleus plants under different environmental conditions by assessing water loss through their stomata.
Purpose of the Experiment
- Measure the rate of transpiration by tracking water loss in plants.
- Investigate how different environmental conditions affect transpiration.
Transpiration Process
- Transpiration is the evaporation of water through stomata (small pores) on the underside of leaves.
- Evaporation through stomata creates a pull that moves water from roots to leaves by bulk flow.
- Guard cells regulate the opening and closing of stomata, thus controlling water loss.
Experimental Setup
- Coleus plants are used because they are shade-growing and have similar size and leaf surface area.
- Four plants are selected to ensure consistency.
- Each plant is watered thoroughly to achieve turgidity before the experiment.
- Plants are bagged completely to prevent soil evaporation, ensuring that only transpiration is measured.
Experimental Conditions
- Plants are exposed to three different variables:
- 24-hour light
- 24-hour darkness
- 12-hour light with wind
- One plant serves as a control under 12-hour light.
- Each plant is labeled according to its assigned condition.
Procedure Details
- Plants are placed in one-gallon bags, removing excess plastic and sealing with a rubber band to prevent air exposure.
- Care is taken not to damage the plant stems during bagging.
- The loss of mass (water loss) over time is measured to determine the rate of transpiration.
Key Terms & Definitions
- Transpiration — loss of water vapor from plant leaves through stomata.
- Stomata — small pores on leaf undersides where gas exchange and water loss occur.
- Guard cells — cells that open and close stomata, regulating transpiration.
- Turgid — the swollen state of a plant when full of water.
- Bulk flow — movement of water from roots to leaves due to evaporation pull.
Action Items / Next Steps
- Place labeled, bagged plants into their assigned environmental conditions.
- Measure and record the mass of each plant at set intervals to calculate water loss.
- Analyze which condition has the greatest or least effect on transpiration.