Transport in Plants Notes – A Level Biology

These A Level Biology notes deal with transport in plants. They start with water stress and the part abscisic acid plays in closing stomata. Next they compare active and passive uptake of mineral ions, giving evidence that uptake is active: ion accumulation, respiratory inhibitors, temperature and oxygen supply. Evidence that ions move in the xylem is also covered. The notes then turn to translocation in the phloem. They explain the mass flow, cytoplasmic streaming and electro-osmosis hypotheses and the limitations of each. Sucrose loading and unloading by transfer and companion cells is described, along with experimental evidence such as aphid stylets, radioactive carbon tracing and bark ringing.