Question

The mechanism by which sugars from leaves are transported through the phloem to growing tissues is called ___.

• A. Pressure flow
• B. Osmotic flow
• C. Diffusion flow
• D. Active gradient flow

Answer 1

The correct option is A

Pressure flow

Pressure flow

The nutrient-rich regions that supply sugars for the rest of the plant are called the sources or the leaves, where sugar is generated through photosynthesis. The contents of the phloem tubes flow from the sources to the growing tissues through into the sieve elements. Water follows the sugar molecules into the sieve elements through osmosis creating turgor pressure in the sieve elements.

The sugar molecules are taken out of the phloem at sinks by active transport which is followed by water osmotically. This results in creation of high water potential and low turgor pressure driving the pressure flow.