2.02 - Transpiration and Transpiration Pull

In the previous section, we examined plant vascular tissues both in form and in function. We have come to understand how the tissues are adapted for their functions (i.e. how are they structured) but we have yet to understand the mechanism by which these substances are transported in the vascular tissues (i.e. how it works). In this section, we will examine water transport in the xylem.
The main mechanism of water transport in flowering plants is transpiration pull. What is transpiration? What is transpiration pull? Let us first view a short clip, by once again, my favourite wild life presenter, Sir David Attenborough, before we begin a deeper discussion:

Transpiration Pull (BBC - Life of Plants)

Now that we have a brief idea of what transpiration is about, let us visit the following links to get a more concrete picture:
  1. Animation on transpiration: http://www.tutorvista.com/content/biology/biology-i/tissues-plants-animals/transpiration-pull.php
  2. Animation on transpiration stream
How do we Measure the Rate of Transpiration?
Let us try a virtual laboratory experiment and examine how we may measure transpiration in the laboratory. As you are working on the virtual experiment, think about how inaccuracies may arise using the experimental set-up to determine transpiration rates.
  1. Simulation Laboratory on measuring Transpiration with the Potometer: http://www.ucopenaccess.org/courses/CPBioLabs/gen_course/index.html
Factors Affecting Rate of Transpiration
So what are the factors that will affect transpiration? Air humidity? Temperature? Light Intensity? How do these factors influence the rate of transpiration? Let us do a quick self-test to identify these factors and see if we can make an intelligent guess of how these factors influence transpiration.
  1. Potometer Simulation with Variable Conditions: http://www.classzone.com/cz/books/bio_09/resources/htmls/virtual_labs/virtualLabs.html (recommended)
  2. http://www.sycd.co.uk/can_we_should_we/explore/plants/potometer-applet.html
  3. http://www.planet-science.com/sciteach/online_resource/software/plants/potometer-applet.html
  4. Factors affecting rate of transpiration Self-Quiz: http://www.phschool.com/science/biology_place/labbench/lab9/factrate.html