Question

Describe what is meant by the following:
1. pressure-flow movement of phloem
2. coupled transport of sucrose

Answer 1

Explanation:

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1. The high turgor pressure drives movement of phloem sap by “bulk flow” from source to sink, where the sugars are rapidly removed from the phloem at the sink. Removal of the sugar increases the Ψs, which causes water to leave the phloem and return to the xylem, decreasing Ψp.
2. The coupling of sucrose transport to the translocation of protons has to be very strong to allow for the high accumulation of sucrose in the phloem vessels and the reversion of transport in sink tissues.