SSC MTS EXAM

Detailed explanation-1: -In very general terms, the pressure flow model works like this: a high concentration of sugar at the source creates a low solute potential (s), which draws water into the phloem from the adjacent xylem. This creates a high pressure potential (p), or high turgor pressure, in the phloem.

Detailed explanation-2: -The Pressure-Flow Hypothesis The pressure is created by the difference in water concentration of the solution in the phloem and the relatively pure water in the nearby xylem ducts. At their “source”-the leaves-sugars are pumped by active transport into the companion cells and sieve elements of the phloem.

Detailed explanation-3: -* Outline why pressure in the phloem increases due to the movement of water into the phloem. The build up of sucrose and other carbohydrates draws water into the companion cells through osmosis. The rigid cell walls combined with the incompressibility of water result in a build-up of pressure.

Detailed explanation-4: -The increased solute concentration causes water to move by osmosis from the xylem into the phloem. The positive pressure that is produced pushes water and solutes down the pressure gradient. So, the correct answer is “Osmosis".