Question

The driving force for the translocation of organic solutes through phloem is __ gradient

Answer 1

Due to the presence of sucrose in the sieve tube cells water enters into sieve tube cells and a hydrostatic pressure builds up. At the sink osmotic pressure is reduced as sugars and removed. Hence water flows out of phloem and into the sink, reducing the hydrostatic pressure in the phloem vessel. This gradient in the hydrostatic pressure facilitates the mass movement in the phloem.