Plants take up water through their roots andthen lose water through structures called stomata during a process called transpiration.
The amount of water a plant loses depends on howoften the stomata open to let water out. Environmental conditions can affectthe opening of stomata. For example, in a hot, dry climate, such as in thedesert, a plant's stomata would often be closed to prevent dehydration. You can test the effects of theenvironment on transpiration with this experiment.
How is transpiration affected by temperature andenvironment?
Plants lose more water through transpiration ina cool environment than in a hot, dry one.
• 2 smallplastic soda bottles, cleaned and dried
• Enough waterto fill the soda bottles
• A sensitivefood scale
• 2 sproutingbean plants with the same number of leaves
• A roll ofaluminum foil
• Enoughmodeling clay to seal the soda bottles
• A desk lampwith a 100-watt bulb Procedure
1. Fill both ofthe soda bottles with the water. Weigh them carefully on the food scale and record their weights.
2. Place the roots of one plant into the water ineach bottle. Wrap the aluminum foil
around the bottom ofthe plant and the mouth ofeach bottle to seal it. Complete the seal with a layer of modeling clay toprevent the water from being lost through evaporation.
3. Place one bottle inindirect sunlight.
4. Place the other bottle about a foot (30 cm) fromthe desk lamp. Position the lamp so the bulb shines directly on the plant. Turnthe light on.
5. Afterthree days, remove the plants, aluminum foil, and modeling clay from bothbottles. Weigh them carefully on the food scale.
6. Calculatethe weight difference between the bottles at the start of the experiment and atthe end. This value gives you an idea of how much water each plant used in thethree days of the experiment.
Did the plant left under thedesk lamp lose less water than the plant in indirect sunlight? Do you think theplant was conserving water because it was in a hot environment?
Bring in one ofthe bottles witha plant to show your audience what you used to do the experiment. Determine whatpercentage ofthe water was used by the plant left in indirect sunlight. Compareit to the percentage used by the plant left under the desk lamp. Make a bargraph to illustrate the difference.
How do you think windyconditions affect transpiration? Repeat this experiment with a plant left neara running table fan instead of a desk lamp.
How do you think humidconditions, such as in a rain forest, affect transpiration? Repeat thisexperiment with a plant that you mist with water every twenty minutes. Reducethe length ofthe experiment to six hours instead of three days—or else, youwould be sick of misting!