AP BIOLOGY

Detailed explanation-1: -The glucose prepared in the leaves is converted into sugar. The sugar in the form of sucrose is moved into the companion cells and then into the living phloem sieve tube cells by active transport. This creates a hypertonic condition in the phloem. Water in xylem vessels adjacent to phloem moves through endosmosis.

Detailed explanation-2: -According to mass flow hypothesis, sucrose moves into the living phloem sieve tube cells by active transport.

Detailed explanation-3: -The addition of sucrose into the sieve tubes increases the concentration of this solute, causing water to flow into the sieve tubes by osmosis. With the entry of water, the sieve tube pressure near the source cells increases and forces the solution to move to regions of lower pressure.

Detailed explanation-4: -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-5: -Active transport is used to load organic compounds into phloem sieve tubes at the source.