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Transpiration (Lab Activity)

Grade Level: 6-8

Time Frame: 40-45 minutes + part of a second class period

Introduction to Lesson:

This lesson is a preparation for the next day’s lesson on transpiration. Students will be setting up their own demonstration of the process of transpiration. It will take the entire period for the students to create an environment for transpiration to occur so that the students can see what exactly transpiration is. This is a fun activity and the students will be amazed to see transpiration in action!

Image source: http://www.bestgardening.com/bgc/images/transpiration05lge.gif

New Jersey Core Curriculum Content Standards: 

STANDARD 5.1 (Scientific Processes) All students will develop problem-solving, decision-making and inquiry skills, reflected by formulating usable questions and hypotheses, planning experiments, conducting systematic observations, interpreting and analyzing data, drawing conclusions, and communicating results.

A. Habits of Mind

·          Recognize that the results of scientific investigations are seldom exactly the same and that replication is often necessary.

B. Inquiry and Problem Solving

·          Identify questions and make predictions that can be addressed by conducting investigations.

·          Design and conduct investigations incorporating the use of a control.

·          Collect, organize, and interpret the data that result from experiments.

C. Safety

·          Know when and how to use appropriate safety equipment with all classroom materials.

·          Understand and practice safety procedures for conducting science investigations.

STANDARD 5.5 (Characteristics of Life) All students will gain an understanding of the structure, characteristics, and basic needs of organisms and will investigate the diversity of life.

A. Matter, Energy, and Organization in Living Systems

·          Explain how the products respiration and photosynthesis are recycle

Standard 5.8: (EARTH SCIENCE) ALL STUDENTS WILL GAIN AN UNDERSTANDING OF THE STRUCTURE, DYNAMICS, AND GEOPHYSICAL SYSTEMS OF THE EARTH.

Strand B: Atmosphere and Water

Cumulative Progress Indicator 2: Describe and illustrate the water cycle.

Objectives: 

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Students will observe transpiration occurring in a plant placed into a simple potometer that they will construct in this activity.

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Students will connect what they see with the process of water movement into and out of a plants’ tissues.

Materials and Resources:

1.      Two plastic cups per student

2.      Square piece of cardboard for between the cups

3.      Plant  shoot (must be provided by teacher or students can bring in but this will not be in the learning trunk)

4.      Vaseline or similar brand of petroleum jelly

5.      Window sill or other light source

6.      Water

7.      Scissors  (warn students to use these carefully especially if cutting woody stems)

Note:  This lesson plan is based on an exercise at: http://www.ucar.edu/learn/1_4_2_18t.htm

Anticipatory Set:  Teacher will hand out an “admit/enter” slip to students asking them to write what they know about how and why humans sweat and plants lose water from their leaves.  If necessary, review the basics of water movement in plants with the students:  Water enters the plant from soil mostly through the  _____________ (roots).  The tissues through which water moves within the plant are called __________________ (xylem). The water then evaporates and moves out of the plant through holes on the undersides of the leaves called _________________ (stomata) whose size is controlled be specialized cells called ___________________ (guard cells). Evaporation rates depend on temperature, wind and humidity levels among other factors.

Sequence Instruction Day 1:            

1.      Using the scissors CAREFULLY, make a small hole (just big enough for the plant stem) in the center of the piece of cardboard.

2.      Take shoots of a healthy broad-leaved plant (e.g. maple, oak, marigold, whatever).  If comparisons are to be made between different treatments, try to match type and size of the shoots so that the results can be meaningfully compared.  Cut the stem on an angle immediately before use, since an angle cut exposes a larger area of the stem for water intake.

3.      Pull the plant stem through the hole and seal around the hole with petroleum jelly.

4.      Fill the bottom cup with a KNOWN amount of water (BE SURE THAT STUDENTS MEASURE THE VOLUME USED AND THAT NO WATER IS LOST AFTER THAT) and place the stem with the cardboard collar into the cup. Cover with the clear plastic cup as shown.  Record the volume of water in the bottom cup in the table provided.

http://www.ucar.edu/learn/images/transpir.gif

5.      Create a “control” terrarium that is identical to that with the living plant but which does not contain the plant itself.  To do this the students could simply cut a hole in a second sheet of cardboard and cover that with petroleum jelly as in the living plant “treatment” and place that into a terrarium just like that.  Alternately, a “fake plant” – either silk or plastic could be inserted in a similar way as the living plant, and the terrarium set up identically to the living plant “treatment”.

6.      Again, fill the bottom cup with a KNOWN amount of water (BE SURE THAT STUDENTS MEASURE THE VOLUME USED AND THAT NO WATER IS LOST AFTER THAT) and place the stem with the cardboard collar into the cup. Cover with the clear plastic cup as shown.  Record the volume of water in the bottom cup in the table provided.

7.      Put the small terrariums in the sun or under a lamp.

8.      In fifteen minutes, you should begin to see droplets of water on the sides of the clear inverted cup over the living shoot but not over the control. More moisture will accumulate in the top cup of the terrarium with the live plant with time, but little to none should be seen in the top cup in the control terrarium.

9.      If possible, leave the terrarium cups set up in the classroom for several days and measure the amount of water transpired (it’s usually easiest to do this by measuring what’s lost from the bottom cup rather than trying to measure what evaporates into the top one).

TABLE FOR RECORDING WATER VOLUMES USED IN THE VARIOUS TERRARIUMS

Treatment

Volume of Water in bottom cup at start of experiment

Volume of Water in bottom cup at end of experiment

Volume of water lost

 

Regular Living Branch

 

 

 

 

 

Control

 

 

 

 

Extension Treatment (if used write in what was done)

 

 

 

 

 

 

Accommodations and Modification:

[None should be needed]

 

Extension Activity

Have some students smear petroleum jelly on either the under or the top side of the leaves on an extra set of living plant shoots (make sure they record which one they did). Compare the water loss through the tissues of the plants without the petroleum jelly to those with the jelly on the different surfaces. This should allow the students to determine from which side of the leaf the majority of water loss occurs.  The teacher can then relate this to the position of the stomata on the leaf surfaces.  NOTE:  As far as possible, match the size of shoots used in the different variants of this experiment to maximize the validity of the comparisons.

Anchor Activity (if lesson goes shorter than planned)

Discuss the scientific method with the students in the context of the experiment.  What was the purpose of the control?  Why would it be important if this was a real experiment to have more than one REPLICATE of each treatment when building conclusions from the results of the experiment?  If living plants DO NOT play a role in speeding up evaporation via transpiration, what would be the prediction about the amount of water in the top cup in the control versus the treatment (same amount, more or less water in the control versus the treatment)?  If living plants DO play a role in speeding up evaporation via transpiration, what would be the prediction about the amount of water in the top cup in the control versus the treatment?  What is the effect of water loss in transpiration for the amount of water in the bottom cup?  What would this mean for plants in soil in the real world?  How would transpiration be expected to affect the water levels in the soil in which the plant is growing?

Closure

Have students write for themselves a hypothesis about what they think will occur with the water levels in the control and treatment cups over the next few days.

Homework

Have the students write answers to the following questions.  Review the answers with them at before starting the new activities at the beginning of the next day’s class.

1.  For each of the following scenarios, would you expect transpiration to occur faster or slower rate than happened in your own experiments in your own classroom?  In each case, explain WHY?

a. If the shoots were placed in a very windy spot.

b. If the shoots were placed in a very humid environment.

c. If the shoots were placed in a classroom that was much warmer than the one in your school.
 

Sequence Instruction Day 2:            

1.      Retrieve the terrariums that you made in your previous class.

2.      Measure the volume of water remaining in the lower cup of each terrarium as accurately as possible (use volumetric flasks, measuring beakers or similar lab equipment if possible).

3.      Fill in the results in the table used to record the initial volumes

4.      Calculate the volume of water lost in each case and write this number in the appropriate column in the table provided.

5.      Have students compare results of similar treatments.  Do all of the replicates from similar treatments show the same results?  If not, what might account for the variability that you see between replicates?

6.      How do the results from the different treatments compare?  Which lost the most water?  Which lost the least?

7.      Review the hypothesis that you made at the end of your last class.  Do your results support your predictions?  Why or why not?

8.      If the extension activities were carried out, what can be concluded about which surface of the leaf is the source of the majority of the water loss through transpiration?  How does this relate to the distribution of stomatal pores on the leaf surface?

HomeworkHave students write up the lab using the appropriate technical terms and scientific formats.

Assessment:  Use a rubric such as the one at http://www.uen.org/Rubric/rubric.cgi?rubric_id=25 to assess student's participation in the activity and their subsequent write up of the experiment and its results.

 

TEACHER FEEDBACK REQUEST:  We are always to working to improve these lesson plans. If you use this lesson plan, we'd love to hear from you with your thoughts, comments and suggestions for future improvements.  Please take the time to fill in our survey at http://www.zoomerang.com/Survey/?p=WEB229JA3BEWBD .  Thanks!

 

© 2009. Jodi Sisk (Author), Louise Wootton and Claire Gallagher (Editors)

 Although the information in this document has been funded wholly or in part by the United States Environmental Protection Agency under assistance agreement NE97262206  to Georgian Court   University, it has not gone through the Agency's publications review process and, therefore, may not necessarily reflect the views of the Agency and no official endorsement should be inferred.

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