Plastoquinones are a group of electron transport molecules between photosystem II and photosystem I in plants. The sequence of carriers is as follows: Pheophytin -> QA -> QB -> QH -> Cytochrome b6f, where QA, QB, and QH are the plastoquinones. Plastoquinone QB and QA are associated with PSII proteins. Electron transfer involving plastoquinones is shown here. Reduction of a plastoquinone creates a plastoquinol.