Transpiration rates (Lupe Anaya)

Research Question and Hypothesis

Question: How do different environmental conditions affect the rate of transpiration in geraniums?

Hypothesis: The rate of transpiration will vary depending on the environmental conditions. The plant kept in a windy environment and under the lamp will loose more water than the plant kept at normal sunlight conditions. The plant kept in the shade will have the least water loss.

Standards

Life Sciences

a.Students know many multicellular organisms have specialized structures to support the transport of materials.

Experimental Design

Provide a description of the experimental design

Independent variable

What is the independent variable? How will you measure the independent variable?

The independent variable is time in days. The mass of the plants is taken everyday at the same time.

Dependent variables

What is the dependent variable(s)? How will you measure the dependent variable(s)?

The dependent variable is the change in mass of each of the plants. The mass will be measured daily using a standard measuring balance. This measurement will indicate the transpiration rate of each of the plants per day, assuming the change in mass is due only to transpiration.

Series

What series will you be testing?

The transpiration rate of each of the plants, as measured by the change in mass per day, will be examined under various environmental conditions, including sunlight, lamp, wind, and shade.

Constants and Controls

What factors are held constant? What serves as a control?

Factors held constant include: same plant species (Pelargonium: geranium), all plants wrapped in plastic bags to prevent direct evaporation from soil, same amount of water added at the beginning of experiment.
The control will be the plant kept in the sunlight near the window for about six hours. The care for geraniums indicate direct sunlight for at least six hours.

Materials

1. Geranium plants can be bought at Walmart. Impatiens are also plants recommended for this experiment.

2. Plastic bags to cover the pots and prevent evaporation from the soil.

3. A scale to measure mass found in the science laboratory.

Procedures

1. Prepare the plants by watering the plants with the same amount of water. If the plants are purchased at the same time then the plants will be similar in watering needs.

2.Cover the plants in plastic bags and tape the bag close to prevent evaporation from the soil.

3. Take the mass of each of the plants and record on a data table.

4. Place each plant under different conditions to be observed: near a window for sunlight, near a fan for windy conditions, under a lamp for hotter environment, and under a table or in a shady area in the classroom.

5. Set the time of the investigation. For this experiment the plants were under these conditions for six hours a day.

6. Take the mass of each plant on a daily basis and record on the data table.

Sample data and graphs

2. Plants and animals have structures for respiration, digestion, waste disposal, and transport of materials. As a basis for understanding this concept:

Analyze the data

The plants under windy conditions and under a lamp were predicted to transpire more than the plant kept in the sunlight and the shade. The results did not support this hypothesis since the plant in windy conditions had the lowest transpiration rates.

Normally, plants in breezy conditions would increase the rate of transpiration from the surface of leaves. This would lower the water potential around the leaf and increase the rate of transpiration. However, if the wind is too strong, the plant will prevent the possibility of extreme water loss by closing the stomata. The fan was kept at the lowest speed but it might still have been too close to the plant and caused the stomata to close during the windy period.

The plant under the lamp is interesting. The first two days the water evaporated was similar to the windy and shady conditions, but then increased compared to the plant in normal sunlight conditions. The lamp was placed a bit farther away after the second day because the clamp broke and might explain the high increase in evaporation. Plants that are not adapted to hot environments will also close their stomata as a result of the heat stress to prevent losing water. This can explain the low transpiration rates the first days and when the light was placed a bit farther away the heat stress was reduced and transpiration increased.

As expected the plant kept near the window for six hours had a higher rate of transpiration rate than the plant kept in the shade. The stomata are normally opened in day light and solar energy would increase transpiration.

Future investigations using this procedure might take into account making the windy and heat conditions less stressful for the plants and having more than one plant at each environmental condition.

References

Lab Bench Activity on Transpiration by Pearson Education

Biology Teaching and Learning Resources by D G Mackean

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