Explain the mechanism of food translocation by the theory of pressure flow mechanism.

The pressure flow mechanism, also known as the mass flow hypothesis, describes the process by which food (mainly sucrose) is transported through the phloem from source tissues (e.g., leaves) to sink tissues (e.g., roots, fruits, and flowers).

At the source, sucrose is actively transported into the sieve tubes of the phloem, which lowers the water potential in the phloem cells. As a result, water from the surrounding xylem enters the phloem by osmosis, creating a pressure difference between the source and sink regions.

At the sink, sucrose is actively unloaded from the phloem into the surrounding cells, which increases the water potential in the phloem. As a result, water moves back into the xylem through osmosis, lowering the pressure at the sink. The pressure difference between the source and sink drives the movement of the phloem sap, which carries sucrose, hormones, amino acids, and other organic compounds necessary for the plant’s growth and development.

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