Campbell Biology (11th Edition)

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

Chapter 7 - 7.2 - Concept Check - Page 132: 2


Movement of water molecules through the lipid bilayer is very slow due to water's molecular polarity/hydrophilic nature. While water can cross the membrane on its own, so much water has to move across membrane during the normal life of a cell that help from a transport protein is needed to provide the required speed of transport.

Work Step by Step

The key here is to see that transport is not just affected by whether a molecule can move on its own but by how much must move. This is analogous with the question in biochemistry of how quickly a reaction can proceed, not just whether it is spontaneous.
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