What is Plant Transpiration?

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Updated on Sep 03, 2014

Grade Level: 5th - 6th; Type: Life Science


What is the project about?

Transpiration is the loss of water from plant leaves. Water exits the leaf through stomata, which are tiny pore spaces in the leaf. The rate of transpiration depends on air temperature and solar radiation. This science fair project will investigate how much water can a plant take up and release in a certain period of time through the process of transpiration.

What are the goals?

Two test tubes or test tube like containers will be filled three-quarters full with water a plant stem will be placed in one of the test tubes. The height of the water in each test tube will be measured and recorded. The water level will be check over a predetermined time period. Based on the results of this investigation data tables will be prepared and the results potted on a graph. This science fair project will support or refute the idea that water is released from plants during a process called transpiration that is caused by evaporation.

Research Questions:

  • What is transpiration?
  • What caused the water to go down in the test tube containing the plant stem?
  • Did the same thing happen in the test tube with water only?
  • What was the calculated rate of transpiration?
  • Using the graph, compare the rate of transpiration with the rate of evaporation alone.
  • What was the control for this investigation?

Transpiration is important for any plant to survive. It keeps water moving in the plant, along with the dissolved mineral salts that the plant needs for nutrition and it helps cool the plant. Much of the water taken up by plants is released through transpiration. It is difficult to separate the processes of evaporation and transpiration, so this transfer of water is sometimes simply called "evapotranspiration."

All plants transpire. The rate of transpiration depends on a plant's physical properties and its environmental conditions. As transpiration occurs mainly on the leaf, a general rule is that plants with larger leaves will transpire more than plants with smaller leaves.

Factors like the humidity of the air surrounding the plant and temperature will affect the rate of transpiration and there must be enough water available in the soil. This project will enable the investigator to connect what he or she sees with the process of water movement into and out of a plant's tissues (leaves).

Any required diagrams/pictures (Pictures speak a thousand words!)

Digital photos can be taken during the experimenting process also the following sites offer down loadable images that can be used on the display board:





What materials are required?

Two test tubes (or cigar tubes), empty metal soup can, plastic wrap, water, marking pen, metric ruler, masking tape, and stopwatch or clock. Also needed is a fresh branch, or pieces of a branch with at least 5 large leaves on it.

Where can the materials be found?

With the exception of the branch and the test tubes all of the items for this project are available locally at most major retail (Wal-Mart, Target, Dollar general, etc) discount department stores also, a Tri-fold cardboard display board can be purchased from an art & crafts supply store. Two test tubes may be borrowed from a high school chemistry teacher, or purchased from a hobby shop. Most toy chemistry sets contains test tubes that can be use in this project.

Experimental Procedure

  1. Fill two test tubes approximately three-fourth full of water. Stand both test tubes in an empty metal can.
  2. To control for water evaporation place sheets of clear plastic wrap over the mouths of one of the test tubes and seal with masking tape.
  3. Use the plant stem to poke a hole into the test tube so that it stands upright in the tube. Seal around the hole with tape.
  4. Use a ruler to measure the height of the water in each test tube. Be sure to hold the test tube level, and measure from the waterline to the bottom of the curve at the bottom of the test tube. Record these measurements in a data table similar to one shown labeled "Initial."
Time Test tube with plant (A) Test tube without plant (B)
After 15 min
After 30 min
After 45 min
After 60 min
  1. Wait 15 minutes, and measure the height of water in each test tube again. Record these measurements in the data table.
  2. Reap step 4 three more times. Record the measurements each time.
  3. Wait 24 hours, measure the height of the water in each test tube. Record these measurements in the data table.
  4. Using the data in the table plot a bar or line graph of the Rate of Transpiration by showing the time (min) along the X-axis verses the water level height (mm) in the test tubes along the Y-axis.
  5. Calculate the rate of transpiration by using following operations:

    Test tube with plant:

    Initial height - Overnight height = Difference in height of water (A)

    Test tube without plant:

    Initial height - Overnight height = Difference in height of water (B)

    Water height difference due to transpiration: Difference A - Difference B = Water lost due to transpiration

    Initial amount of water Amount of water left after 24 hours Amount of water lost
    Tube with plant branch
    Tube without branch
  6. To calculate the rates of transpiration and evaporation per hour use the following formulas: Amount of water lost ÷ 24 hours = ________ water transpired /hour Amount of water lost ÷ 24 hours = ________ water evaporation/hour

Terms/Concepts: Transpiration; evaporation; evapotranspiration; stomata; solar radiation



Title: How Do Plants Grow?

Author: Melissa Stewardt

Publisher: Cavendish, Marshall Corporation ISBN-13: 9780761433668 and ISBN: 076143366X

This five-chapter 32-page book explains the basics of plant photosynthesis. In the chapter "What Plants Need to Grow," the author describes how plant leaves collect energy from the sun and release water and oxygen to the atmosphere, while the roots absorb water and minerals from the soil this action makes transpiration possible.

Links to related sites on the web

Title: Transpiration

URL: http://techalive.mtu.edu/meec/module01/Transpiration.htm

Title: Transpiration

URL: http://www.uwsp.edu/geo/faculty/ritter/geog101/textbook/biogeography/transpiration.html

Title:Transpiration Lab

URL: http://www.directessays.com/viewpaper/80772.html

NOTE: The Internet is dynamic; websites cited are subject to change without warning or notice!

Mike Calhoun is a consultant for the National Science Teachers Association, a veteran science teacher, and hosts an online science website. Over the years Mike has studied trends in science, education, and finance, conducting research, developing programs, and writing articles on these topics.

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