Some questions on the herbicide triazine: Triazines block the photosystem II complex in the electron transport chain in the thylakoid membrane of plants. This occurs because triazine attaches to the D1 protein in Photosystem II at the same position where plastoquinone A should attach. Triazine resistant weeds are prevalent and present a major agricultural problem. 1. How is the functioning of the electron transport chain and process of phosynthesis affected by the presence of triazine molecules? 2. How could a plant be resistant to triazine molecules? 3. Why have these weeds become a widespread problem in the environment?