AP BIOLOGY

Detailed explanation-1: -Sucrose is loaded into sieve tube cells by active transport. Again active transport is necessary to move sucrose out of sieve tube cells.

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

Detailed explanation-3: -Once the sucrose reaches the phloem tissue in a source, it needs to be actively transported into the companion cells and sieve tube members. This process does require energy, and this is why the companion cells must have many mitochondria to release this energy through cellular respiration.

Detailed explanation-4: -Phloem: Active transport of sucrose from source cells into phloem sieve tube elements (energy required)

Detailed explanation-5: -Phloem Loading Mechanisms This is a thermodynamically active process that uses the proton gradient as an energy source.