Passive Absorption Summary
Prior to herbicides reaching their sites of action and killing the plant, they must first enter the plant cell where that site of action resides. Most herbicides are able to enter a plant cell by passing through the cell membrane, as driven by their concentration gradient (termed passive diffusion), a process that requires no energy. Even though most herbicides are passively absorbed, some herbicides are able to accumulate in the alkaline cytosol to concentrations greater than outside the cell, because of ion trapping. In addition to ion trapping, the processes of metabolism and binding to cell walls or lipids can also increase the concentration of the herbicide in the cell. However, in these cases, the herbicides are usually rendered non-toxic.