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Activity (Hands-On)Grades 6 - 9

Just Breathe Green: Measuring Transpiration Rates

Through multi-trial experiments, students are able to see and measure something that is otherwise invisible to them—seeing plants breathe. Student groups are given two small plants of native species and materials to enclose them after watering with colored water. After being enclosed for 10, 20, and 30 minutes, teams collect and measure the condensed water from the plants' "breathing," and then calculate the rates at which the plants breathe. A plant's breath is known as transpiration, which is the flow of water from the ground where it is taken up by roots (plant uptake) and then lost through the leaves. Students plot volume/time data for three different native plant species, determine and compare their transpiration rates to see which had the highest reaction rate and consider how a plant's unique characteristics (leaf surface area, transpiration rate) might figure into engineers' designs for neighborhood stormwater management plans.

Four photographs show an evapotranspiration time series for a Florida native plant species with the common name, Yellowtop. First photo shows several of the same little green plants with long leaves planted near each other, surrounded by bark mulch. In the next three photos, one plant is covered by an inverted clear plastic cup that is increasingly opaque with condensation building up inside.Do plants breathe?

Estimating the total amount of water within various processes of the water cycle has been a topic of scientific exploration for more than 150 years and a central focus of hydrology. Practical applications of hydrology are found in such tasks as the design and operation of hydraulic structures, water supply, wastewater treatment and disposal, recreational use of water, and fish and wildlife protection. The role of applied hydrology is to analyze the problems involved in these tasks and provide guidance for planning, and management of water resources. Like engineers, students account for a component of the water budget, calculating the rate of a reaction. Being able to understand and calculate rates is important to engineering design, modeling and research.

After this activity, students should be able to:

  • Explain what the rate of a reaction is and how it applies to the urban water cycle.
  • Calculate the transpiration rate of reaction for a plant species.
  • Create a graph of collected data and select native plant species based on transpiration data.

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