JoVE Lab Manual
Lab Bio
Lab Bio
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Transpiration
Transpiration
Learning Objectives
At the end of this lab, students should know...
What is transpiration?
Transpiration is the process of plants in which they absorb, distribute and subsequently release water. Evaporation is the movement of water to the air, while guttation specifically refers to secretion of droplets of water from the pores of plants. Both processes combined make up transpiration in plants.
What is the mechanism of transpiration?
Water potential drives the uptake of water from the root hairs and also in transporting water to the tips of leaves. When evaporation is high in leaves, this creates areas with lower water potential, or areas with less water, so water from the roots and stem is driven to the leaves.
Why do plants transpire?
Transpiration allows carrying water and nutrients towards the photosynthesizing parts of the plant, and thus allows plant growth.
How do plants in different environments regulate transpiration?
Some plants in hot and arid environments open their stomata for gas exchange at night in order to reduce water loss. Some others have reduced leaf surface area, fewer stomata, or hairs on their leaves. On the other hand, in humid environments such as rainforests, plants transpire quickly in order to outgrow their competing neighbors or grow tall enough to avoid being eaten by herbivores.
Why study transpiration?
We can learn how plants adapt to different environments. Moreover, we can study how current environmental changes affect plants and their ecosystem. Moreover, we can also use transpiration studies to identify crops that can grow in a specific climate.
List of Materials
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Leaves from four plant species (2-4/each)5
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Rubber tubing (~50 cm piece)5
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Calibrated 5 mL pipette5
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Pipette bulb5
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Stand with two clamp5
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Dropper/tranfer pipette5
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Lubricant (petroleum jelly)5
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Flat plastic conatainer5
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Transparent ruler5
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Razor blade5
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Timer5
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Clear nail polish ( 15mL)5
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Clear cellophane tape5
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Microscope Slides5
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Scissors5
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White paper sheets25
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Weighing scale (minmum 1)Dependent on the lab size
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Microscope (minmum 1)Dependent on the lab size
Lab Prep
- Comparing Transpiration Rates of Leaves
- Before beginning the experiments, gather leaves from four plant species that represent different ecological strategies, so that you have enough for one set of leaves per student. NOTE: If leaf-bearing plants are not available locally, an alternative is to grow the plant species of interest in the laboratory, or to purchase plants from a gardening store.
- Next, cut lengths of rubber tubing to make roughly 50 cm sections and place one piece alongside a 5 mL pipette at each student workstation.
- Then, set out a bucket or tray of water and ensure students have access to the appropriate clamps and stands.
- Finally, set out bottles of clear nail polish, as well as clear tape and clean microscope slides for the stomata exercise.
