Overview and Objectives

Herbicides are effective because they each target a specific metabolic pathway in plants. In order for a herbicide to kill a plant, it must first be absorbed by the plant’s leaves or roots. Once the herbicide is absorbed, it will enter a cell which possesses the metabolic pathway the herbicide was designed to target. This lesson follows the fate of the herbicide after it has entered the plant via leaf or root tissue, and explains the factors controlling transport of a herbicide into plant cells. This lesson describes 1) the barriers to herbicide entry, such as the plant cell membrane, 2) the role that the herbicide’s chemical properties have on the rate of cellular absorption, and 3) experimental approaches to understanding herbicide absorption at the cellular level.

At the completion of this lesson, students will be able to:

1. Define lipophilicity and hydrophilicity;
2. Compare and contrast passive and active transport across membranes;
3. Identify the factors controlling herbicide transport across membranes;
4. Explain ion trapping of weak acids; and
5. Identify experimental approaches to characterizing modes of herbicide transport across membranes.