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By Maryann Adel Borsick Herman1, J. Phil Gibson2

1. St. John Fisher College 2. University of Oklahoma

In this lab, students will examine differences between C3 and C4 plants in their transpiration rates.

Listed in Teaching Materials | resource by group Plants by the Numbers

Version 1.0.0 - published on 06 Jun 2018 doi:10.25334/Q4B39W - cite this

Licensed under CC Attribution-ShareAlike 4.0 International according to these terms

Adapted from: Transpiration v 1.0


In this laboratory exercise, you will investigate different structural and functional aspects of transpiration. You will observe different components of the plant vascular system and conduct an experimental manipulation of corn (Zea mays), a C4 plant, and sunflower (Helianthus annuus), a C3 plant. The results of this exploration will demonstrate the fundamental principles of transpiration and the function of plant structures in this important physiological process.

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Researchers should cite this work as follows:



Final Product BSA 2018: Growing Quantitative Literacy Using Botany

Name and Institution:  Maryann Herman, St. John Fisher College

Course/Course format: BIOL 213 lecture and lab - plant biology

Module:  Transpiration: HHMI BioInteractive (2018).  Gibson, J. P. (2018). Transpiration. Botanical Society of America, QUBES. doi:10.25334/Q4710V


Seed Dispersal in Tropical Forests: CC Attribution-NonCommercial-NoDerivatives 4.0 International HHMI BioInteractive (2018). Seed Dispersal in Tropical Forests. HHMI BioInteractive, QUBES. doi:10.25334/Q4GH4C




For the spring 2018 semester, I implemented the transpiration lab into my sophomore level plant biology course (BIOL 213).  My main goal was to see how students responded to and learned from the modules so I could then modify (if needed) for future class use. 


  1. Course LOs addressed by module:


  • Describe transpiration and the tension-cohesion theory.
  • Explain what influences water potential and how water potential influences water movement.
  • Describe how different environmental conditions impact rates of transpiration


  1. Implementation of module


Students were given the transpiration handout predominantly unmodified.  I changed the textbook pages to reflect our textbook and plants used were ornamental millet (C4 plant) and petunia (C3 plant).  Seedlings were only about three weeks old.  Additionally, students examined all potential plants in the green room and surrounding building to visualize differences in stomata morphology.


  1. Assessment of Module


On the final lab practical for BIOL 213L, I asked students the following questions regarding the transpiration lab.Regarding the Transpiration lab:


B. Explain two reasons why our results were inconsistent when measuring the transpiration differences between millet and petunia?



The failure to see any significant change in plant weight allowed for a great discussion of troubleshooting.Students understood what we were using the slides to visualize differences in stomatal number and arrangement on leaves.Student explanations for experimental error and suggestions for improvement ranged from modifications to the type and age of plants, experimental error (not completely sealing the bags), increasing sample size, using a different time interval, examining individual leaves in a closed system.


  1. Reflections on module and ideas for future use

Visualizing guard cells:

Having students make their own slides was a surprisingly fun activity.The lab has moved away from traditional botanical exploration of microscopic plant features.Students really enjoyed visualizing the bizarre shapes of stomata and leaf epidermal cells.To improve:

  • I need to be more vigilant with students who choose leaves where the undersurface looks similar to the upper surface as some switched and thought they were only seeing stomata on the top. 
  • We don’t have reticles in all scopes, so not all students knew the size they were measuring for comparison.  In the future, we could purchase more reticles or have students mark the 1 cm2 area with a marker so they can have more consistency in measurement.


Measuring transpiration between a monocot and dicot

Students do not enjoy sitting and waiting for data measurements, which at times led to careless/rushed data collection.Additionally, I noticed inconsistency in how students sealed bags (ie. some pushed air out while others didn’t).Their results were variable with in replicates (ie. no consistency in millet weight increasing or decreasing).To improve:

  • Verify the method (demonstrate to class than check)
  • Use older/different plants
  • Potentially tie to Vernier Labquest 2 data collection devices

Plants by the Numbers

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