2001 AIPMT Transport in PlantsPhloem transport - pressure flow hypothesis Easy Question 2 of 2 in Phloem transport - pressure flow hypothesis

Loading of phloem is related to : -

A Increase of sugar in phloem
B Elongation of phloem cell
C Separation of phloem parenchyma
D Strengthening of phloem fibre

The answer is A.

Solution

Phloem loading is the movement of sugars (mainly sucrose) from the mesophyll cells (source) into the sieve tubes of the phloem, mostly by active transport.
This increases the sugar concentration in the phloem, so water enters the sieve tubes by osmosis and builds up pressure, which drives the mass flow of sap towards the sinks (Münch's pressure flow hypothesis).
So phloem loading is related to the increase of sugar in the phloem.

Concept Phloem loading

Phloem transport - pressure flow hypothesis in past papers

2 questions from this chapter have appeared across 2 exam years.