What is the First Step in the Pressure Flow Mechanism

Question

What is the first step in the pressure flow mechanism of translocation?
A) Sugar is loaded into the xylem at the source.
B) Sugar is loaded into the phloem at the source.
C) Water is loaded into the phloem at the source.
D) Water is loaded into the phloem at the sink.

Accepted Answer

The first step in the pressure flow mechanism of translocation is that sugar is loaded into the phloem at the source. This creates a high concentration of sugar in the phloem, which causes water to move from the xylem into the phloem by osmosis. This increased water pressure causes the phloem sap to flow towards the sink, where the sugar is unloaded.