Which of the following mechanism can explain the transport of sucrose from source to sink?
a)	Osmotic movement of water into sugar loaded sieve tube cells which create a higher hydrostatic pressure into the source than in the sink
b)	Tension created by differences in pressure potential between source and sink
c)	Active absorption of sucrose through sieve tube membrane driven by a specific pump
d)	Transpiration and active transport of sugar from source to sink

(a)

Munch (1930) proposed the pressure flow hypothesis which best explain the transport of organic nutrients from the source (supply) to sink (utilisation site). According to this theory, source shows a high osmotic concentration than the sink.

When the organic substances from mesophyll cells are (act as source) passed to the sieve tube of phloem through their companion cell by active transport, a high osmotic concentration is developed in sieve tube and acts as a source. Water is absorbed by sieve tubes from the adjacent xylem and develop a high turgor pressure. Thus, the transpiration of organic nutrient takes place from a region of higher turgor region to the area of lower turgor pressure