AP BIOLOGY

Detailed explanation-1: -Phloem: Active transport of sucrose from source cells into phloem sieve tube elements (energy required)

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: -After sugars are produced in photosynthesis, these sugars must be transported to other parts of the plant for use in the plant’s metabolism. Part of the pressure-flow theory is that the sucrose produced is moved by active transport into the companion cells of the phloem in leaf veins.

Detailed explanation-4: -Companion cells contain many mitochondria to provide the ATP needed for the active transport of hydrogen. A high concentration of hydrogen ions builds up in the mesophyll cells. The hydrogen move back into the companion cells, down a concentration gradient using a co-transporter protein.

Detailed explanation-5: -phloem is the living tissue that transports the soluble organic compounds made during photosynthesis and known as photosynthates, in particular the sugar sucrose, to parts of the plant where needed. This transport process is called translocation.