Campbell Biology (11th Edition)

Published by Pearson
ISBN 10: 0-13409-341-0
ISBN 13: 978-0-13409-341-3

Chapter 36 - Test Your Understanding - Level 3 - Synthesis/Evaluation - Page 802: 13


The water molecule in the soil of the forest shown would probably not be moved by root pressure since it is clearly a sunny day in the picture. The molecule would enter the root by osmosis, drawn in by the lower solute potential of the root cells compared to that of the soil. The molecule might cross the plasma membrane, probably via an aquaporin, or it might stay in the cell wall. In either case it would be pulled further into the root by the pull of the tension created by transpiration from leaves far above. If it stayed in the cell wall, the molecule would be forced by the hydrophobic Caparison strip in the endodermis to enter the cytoplasm at that point. It would then move into the xylem and proceed up the stem, relying on cohesion with other water molecules and adhesion to xylem cell walls to help it be drawn up the stem to the leaves, again driven by tension.

Work Step by Step

Review the normal path of water moving from the roots to the leaves, and add in what brings the water into the root. Be sure to include details like the Caspian strip and the role of aquaporins.
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