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A-Level Biology OCR A

Phloem Cells Conc Gradient Maintained Sucrose Surrounding Moves

Phloem unloading occurs as sucrose diffuses out of the phloem into surrounding cells, and a concentration gradient is maintained by rapidly converting sucrose into other substances; solute loss also causes water to move out of the phloem.

La descarga del floema ocurre cuando la sacarosa se difunde fuera del floema hacia las células circundantes, y se mantiene un gradiente de concentración al convertir rápidamente la sacarosa en otras sustancias; la pérdida de solutos también provoca la salida de agua del floema.

Front Describe the process of phloem unloading and explain how a conc gradient is maintained from the phloem into cells requiring sucrose.
Back Phloem unloading:
  • Sucrose diffuses from phloem into surrounding cells at any point into cells that need it
  • Sucrose rapidly moves into other cells by diffusion/converted into another substance so that conc gradient is maintained
  • Loss of solutes causes rise in water potential of phloem - water moves out into surrounding cells by osmosis, some drawn into transpiration stream

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