NEET BIOLOGY

Detailed explanation-1: -According to mass flow hypothesis, sucrose moves into the living phloem sieve tube cells by active transport. Active transport is a mode of transport which requires energy to go against the concentration gradient i.e, moving from a region of low concentration to a region of high concentration with the help of energy.

Detailed explanation-2: -The sucrose is actively transported against its concentration gradient (a process requiring ATP) into the phloem cells using the electrochemical potential of the proton gradient. This is coupled to the uptake of sucrose with a carrier protein called the sucrose-H+ symporter.

Detailed explanation-3: -Phloem: Active transport of sucrose from source cells into phloem sieve tube elements (energy required)

Detailed explanation-4: -Active transport is used to load organic compounds into phloem sieve tubes at the source.

Detailed explanation-5: -Sucrose is loaded into sieve tube cells by active transport. Again active transport is necessary to move sucrose out of sieve tube cells.